- Butanolysis of 4-methylbenzenediazonium ions in binary n-BuOH/H 2O mixtures and in n-BuOH/SDS/H2O reverse micelles. Effects of solvent composition, acidity and temperature on the switch between heterolytic and homolytic dediazoniation mechanisms
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We investigated the effects of solvent composition, acidity and temperature on the switch between heterolytic and homolytic mechanisms in the course of the butanolysis of 4-methylbenzenediazonium (4MBD) ions in binary BuOH/H 2O mixtures and in reverse micelles, RMs, composed of n-BuOH, H 2O and sodium dodecyl sulfate, SDS, by employing a combination of spectrometric (UV/vis) and chromatographic (HPLC) techniques. In reaction mixtures with high n-BuOH percentages, S-shaped variations of kobs with acidity, defined hereafter as -log([HCl]), are obtained with rate enhancements of up to ~370-fold on going from -log([HCl]) = 2 to 6, with inflection points at -log[HCl] ~ 4. HPLC analyses of the reaction mixtures show that the substitution product 4-cresol, ArOH and the reduction product toluene, ArH, are formed competitively. The variation of their yields with acidity is also S-shaped, so that at high acidities (-log[HCl] obs and of the product yields with acidity are found in the -log[HCl] = 3-5 range, suggesting that a turnover in the dediazoniation mechanism takes place under acidic conditions. The results can be interpreted in terms of two competitive reaction pathways, one heterolytic, involving a rate-determining formation of an extremely reactive aryl cation that traps the nucleophiles available in its solvation shell leading to the formation of substitution products (DN + AN mechanism) and a second route where the BuOH reacts with 4MBD to yield an unstable O-adduct of the type Ar-NN-O-R (diazo ether) in a rapid pre-equilibrium step that initiates a radical process leading to the formation of the reduction product ArH (O-coupling mechanism). The results illustrate how the heterolytic and homolytic mechanisms can be switched by just changing the acidity of the solution. Kinetic analyses of the variations of kobs with acidity at different temperatures allowed us to separate kobs into the components for the heterolytic pathway, kHET, and that for the homolytic one, kHOM, to determine relevant thermodynamic parameters for both reaction pathways and for the equilibrium constant K for the formation of the O-adduct Ar-NN-O-R.
- Fernandez-Alonso, Alejandra,Pastoriza Gallego, Ma Jose,Bravo-Diaz, Carlos
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- CoMo sulfide-catalyzed hydrodeoxygenation of lignin model compounds: An extended reaction network for the conversion of monomeric and dimeric substrates
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In the present work, extensive hydrodeoxygenation (HDO) studies with a commercial sulfided CoMo/Al2O3 catalyst were performed on a library of lignin model compounds at 50 bar hydrogen pressure and 300 °C in dodecane, using a batch autoclave system. The catalyst was activated under hydrogen atmosphere prior to the reaction, and the spent catalyst was analyzed using thermogravimetric analysis. An extended reaction network is proposed, showing that HDO, demethylation, and hydrogenation reactions take place simultaneously. HDO of mono-oxygenated substrates proved to be difficult at the applied conditions. Starting from most positions in the network, phenol, and cresols are therefore the main final products, suggesting the possibility of convergence on a limited number of products from a mixture of substrates. HDO of dimeric model compounds mimicking typical lignin linkages revealed that coumaran alkyl ethers and β-O-4 bonds can be broken, but 5-5′ linkages not.
- Jongerius, Anna L.,Jastrzebski, Robin,Bruijnincx, Pieter C.A.,Weckhuysen, Bert M.
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- Structural basis for a Kolbe-type decarboxylation catalyzed by a glycyl radical enzyme
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4-Hydroxyphenylacetate decarboxylase is a [4Fe-4S] cluster containing glycyl radical enzyme proposed to use a glycyl/thiyl radical dyad to catalyze the last step of tyrosine fermentation in clostridia. The decarboxylation product p-cresol (4-methylphenol) is a virulence factor of the human pathogen Clostridium difficile. Here we describe the crystal structures at 1.75 and 1.81 A resolution of substrate-free and substrate-bound 4-hydroxyphenylacetate decarboxylase from the related Clostridium scatologenes. The structures show a (βγ)4 tetramer of heterodimers composed of a catalytic β-subunit harboring the putative glycyl/thiyl dyad and a distinct small γ-subunit with two [4Fe-4S] clusters at 40 A distance from the active site. The γ-subunit comprises two domains displaying pseudo-2-fold symmetry that are structurally related to the [4Fe-4S] cluster-binding scaffold of high-potential iron-sulfur proteins. The N-terminal domain coordinates one cluster with one histidine and three cysteines, and the C-terminal domain coordinates the second cluster with four cysteines. Whereas the C-terminal cluster is buried in the βγ heterodimer interface, the N-terminal cluster is not part of the interface. The previously postulated decarboxylation mechanism required the substrate hydroxyl group in the vicinity of the active cysteine residue. In contrast to expectation, the substrate-bound state shows a direct interaction between the substrate carboxyl group and the active site Cys503, while His536 and Glu637 at the opposite side of the active site pocket anchor the hydroxyl group. This state captures a possible catalytically competent complex and suggests a Kolbe-type decarboxylation for p-cresol formation.
- Martins, Berta M.,Blaser, Martin,Feliks, Mikolaj,Ullmann, G. Matthias,Buckel, Wolfgang,Selmer, Thorsten
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- Characteristic Effect of Pyridine on the NIH Shift and Selectivity in the Monooxygenation of Aromatic Compounds Catalyzed by a Nonheme Iron Complex/Hydroquinones/O2 System
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The high values of the NIH and Me-NIH shifts were observed in the hydroxylation of aromatic compounds such as toluene and xylenes with O2 by the catalytic system in the title.The pyridine concentration greatly affected not only the NIH shift, but the selectivity to form phenols by hydroxylation of the aromatic ring and to form aldehydes by oxidation of the methyl group.
- Funabiki, Takuzo,Toyoda, Takehiro,Yoshida, Satohiro
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- Raney Ni-Al alloy-mediated reduction of alkylated phenols in water
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Raney Ni-Al alloy in a dilute aqueous alkaline solution has been shown to be a very powerful reducing agent in the hydrogenation of phenol and alkylated phenols to the corresponding cyclohexanol derivatives.
- Tan, Song-Liang,Liu, Guo-Bin,Gao, Xiang,Thiemann, Thies
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- Highly dispersed molybdenum carbide nanoparticles supported on activated carbon as an efficient catalyst for the hydrodeoxygenation of vanillin
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Characterized by XRD and TEM, highly dispersed molybdenum carbide (Mo2C) nanoparticles with a diameter of 1-4 nm were effectively synthesized on activated carbon at 700 °C. The Mo2C-based catalyst exhibited high activity and stability for the hydrodeoxygenation (HDO) of vanillin under mild conditions (100 °C, 1.0 MPa of H2, 3 h) in aqueous solution. According to the distribution of products with time, a HDO mechanism involving vanillyl alcohol as an intermediate product was proposed. Moreover, after being recycled several times, the loss of catalytic activity was negligible, which demonstrated that the Mo2C-based catalyst had the property of resistance to deactivation.
- He, Lili,Qin, Yu,Lou, Hui,Chen, Ping
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- Aerobic homocoupling of phenylboronic acid on Mg-Al mixed-oxides-supported Au nanoparticles
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Au nanoparticles are highly dispersed on Mg-Al mixed oxides by anion exchange (Au/MAO-AE) and homogeneous deposition-precipitation (Au/MAO-HDP). The XRD, UV-visible, and XPS spectra demonstrate that the Au species on both samples are present as metallic Au. The Au nanoparticles are directly confirmed by the transmission electron microscopy images. Very importantly, both Au/MAO-AE and Au/MAO-HDP catalysts show superior catalytic activity, selectivities, and recyclabilities in the aerobic homocoupling of phenylboronic acid, yielding biphenyl and phenol. During this reaction, H2O molecules from the system and hydroxyl groups on Mg-Al mixed oxides strongly influence the catalytic performance. Based on the catalytic data and XPS characterizations, a mechanism for aerobic homocoupling of phenylboronic on metallic Au nanoparticles is proposed. These catalytic data are in good agreement with those obtained from theoretical calculations.
- Wang, Liang,Wang, Hong,Zhang, Wei,Zhang, Jian,Lewis, James P.,Meng, Xiangju,Xiao, Feng-Shou
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- Catalysis of the Methoxyaminolysis of Phenyl Acetate by a Preassociation Mechanism with a Solvent Isotope Effect Maximum
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General-acid catalysis of the reaction of methoxyamine with phenyl acetate by the proton, carboxylic acids, and ammonium ions follows a nonlinear Broensted curve.This curve agress quantitavely with the behavior expected for the enforced preassociation mechanism of catalysis that was predicted for this reaction.The stronger acids, including the proton, follow a Broensted slope of α=0.16 that represents rate-limiting amine attack assisted by hydrogen bonding, weaker acids react with partially rate-limiting proton transfer to the addition intermediate T+/-, and the weakest acids follow a steeper Broensted slope approaching α=1.0 that represents rate-limiting separation of the protonated intermediate T+.There is no decrease in the rate constant for catalysis by chloroacetic acid with increasing viscosity in water-glycerol mixtures; a decrease is observed for the reaction of methylamine with p-tolyl acetate catalyzed by acetate buffers, which is believed to proceed by a diffusion-controlled trapping mechanism.A sharp maximum in the solvent isotope effect at pKHA = 6.8 confirms the kinetically significant proton-transfer step in the intermediate region near ΔpK = 0.The decrease with stronger acids represents a decrease in the isotope effect for this proton-transfer step, which is largely rate limiting for acids of pKa = 4-7, but the decrease with weaker acids can be explained by the change to rate-limiting diffusional separation of T+ and A-.Two explanations are offered for the decreased isotope effect with increasing acid strengh. (1) There is a sharp change to an asymmetric structure of the transition state for the very rapid proton-transfer step, as suggested by Melander and Westheimer. (2) There is a shift to a rate-limiting change in solvation that occurs immediately either before or after the proton-transfer step with stronger acids.It is possible to fit the observed Broensted curve and isotope effect maximum with calculated rate constants that are based on a rate law and estimated rate constants for the steps of the latter mechanism.
- Cox, Michael M.,Jencks, William P.
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- One step phenol synthesis from benzene catalysed by nickel(ii) complexes
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Nickel(ii)complexes of N4-ligands have been synthesized and characterized as efficient catalysts for the hydroxylation of benzene using H2O2. All the complexes exhibited Ni2+ → Ni3+ oxidation potentials of around 0.966-1.051 V vs. Ag/Ag+ in acetonitrile. One of the complexes has been structurally characterized and adopted an octahedral coordination geometry around the nickel(ii) center. The complexes catalysed direct benzene hydroxylation using H2O2 as an oxygen source and afforded phenol up to 41% with a turnover number (TON) of 820. This is unprecedentedly the highest catalytic efficiency achieved to date for benzene hydroxylation using 0.05 mol% catalyst loading and five equivalents of H2O2. The benzene hydroxylation reaction possibly proceeds via the key intermediate bis(μ-oxo)dinickel(iii) species, which was characterized by HR-MS, vibrational and electronic spectral methods, for almost all complexes. The formation constant of the key intermediate was calculated to be 5.61-9.41 × 10-2 s-1 by following the appearance of an oxo-to-Ni(iii) LMCT band at around 406-413 nm. The intermediates are found to be very short-lived (t1/2, 73-123 s). The geometry of one of the catalytically active intermediates was optimized by DFT and its spectral properties were calculated by TD-DFT calculations, which are comparable to experimental spectral data. The kinetic isotope effect (KIE) values (0.98-1.05) support the involvement of nickel-bound oxygen species as an intermediate. The isotope-labeling experiments using H218O2 showed 92.46% incorporation of 18O, revealing that H2O2 is the key oxygen supplier to form phenol. The catalytic efficiencies of complexes are strongly influenced by the geometrical configuration of intermediates, and stereoelectronic and steric properties, which are fine-tuned by the ligand architecture.
- Muthuramalingam, Sethuraman,Anandababu, Karunanithi,Velusamy, Marappan,Mayilmurugan, Ramasamy
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- Hydrolysis of aryl N-methyl-N-arylsulfonylcarbamates
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Tertiary sulfonylcarbamates 1 were prepared by reaction of a sulfonamide anion with aryl chloroformates. These previously unreported compounds hydrolyse in aqueous media to the parent sulfonamide and phenol. The pH-rate profile shows both spontaneous and base-catalysed processes. The reaction is also catalysed by buffers. Kinetic data for the hydrolysis of these compounds by HO- are best interpreted in terms of a mechanism involving rate-limiting formation of a tetrahedral intermediate from nucleophilic attack of hydroxide ion at the carbamate carbonyl carbon atom. For the 4-nitrophenylsulfonyl compound 1h decomposition of the tetrahedral intermediate appears to be rate-limiting with the sulfonamide anion, rather than the phenoxide, functioning as the leaving group. The buffer-catalysed process is consistent with general base-catalysed attack of water at the carbamate carbonyl carbon atom.
- Araujo,Campelo,Iley,Norberto
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- Supported Au nanoparticles as efficient catalysts for aerobic homocoupling of phenylboronic acid
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Au nanoparticles with small sizes (1-4 nm) were effectively formed on Mg-Al mixed oxides (Au/MAO), which showed superior catalytic performances and good recyclability in aerobic homocoupling of phenylboronic acid.
- Wang, Liang,Zhang, Wei,Sheng Su, Dang,Meng, Xiangju,Xiao, Feng-Shou
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- Synthesis and antiradical activity of hybrid antioxidants based on isobornylphenols
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Alkylation of isobornylphenols with allylbenzene in the presence of homogeneous and heterogeneous catalysts of different nature has been studied. The maximum yield of phenols containing isobornyl and 1-phenylpropyl moieties has been achieved in the presen
- Chukicheva, I. Yu.,Sukrusheva,Mazaletskaya,Kuchin
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- Mechanism of the Non-Aryne Hydroxydehalogenation of Unactivated Aryl Halides
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The hydroxydehalogenation of aryl halides upon reaction with aqueous alkali at temperatures up to 333 deg C was examined to determine the nature of an ipso hydroxydehalogenation process reported in 1957 to compete with the aryne mechanism.The reactions of p-iodo-, p-bromo-, and p-chlorotoluene with aqueous solutions of sodium or potassium hydroxide or carbonate, carried out in Pyrex glass tubes with exclusion of traces of transition metals, led in all cases to the same product distribution. m-Cresol and p-cresol, the two main products, formed with a para/meta ratio of0.82+/-0.03, consistent with the occurence of the aryne mechanism only.Addition of traces of copper salts or conducting the reaction in a Monel bomb, as done by other investigators, caused the occurence of a non-aryne ipso hydroxydehalogenation.This effect was not produced by nickel, iron, manganese, or cadmium.The ipso hydroxydehalogenation observed in previous studies is identified as a copper-catalyzed process.
- Zoratti, Mario,Bunnett, J. F.
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- Kinetics of Electron-transfer Reactions of para-Substituted Phenols p-C6H4(X)OH with 3+ (phen = 1,10-phenantroline) and with 2- in Aqueous Acidic Solutions: Correlation between the Hammett Constant of X and the One-electron Redox Potential of p-C6H4(X)OH
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Kinetic Studies of the electron-transfer reactions of p-C6H4(X)OH (X= H, OCH3, OH, NH2, or NH3+ with tris(1,10-phenanrtoline)iron(III), 3+, and with hexachloroiridate(IV), 2-, have been made in aqueous acidic solutions.The second-order rate constants (k0) follow the rate law -d/dt = k0, where A is the one-electron acceptor 3+ or 2-, and were determined at an ionic strength of 1.0 mol dm-3 and 25 deg C.The order of the forward rate constants (kf) for the one-electron transfer step, which are defined as k0 = 2kf for the other X, was H + 3+ and 1 : 150 : 75 : 4x1E4 : 7.2x1E4 : 1.0x1E8 in the case of the 2- reactions.By applying Marcus theory to kf, standard redox potentials for the radical cations p-C6H4(X)OH.+ were estimated and found to be well correlated with the Hammett constants (?p) for the para substituents X.
- Kimura, Masaru,Kaneko, Yukari
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- Strong Visible-Light-Absorbing Cuprous Sensitizers for Dramatically Boosting Photocatalysis
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Developing strong visible-light-absorbing (SVLA) earth-abundant photosensitizers (PSs) for significantly improving the utilization of solar energy is highly desirable, yet it remains a great challenge. Herein, we adopt a through-bond energy transfer (TBET) strategy by bridging boron dipyrromethene (Bodipy) and a CuI complex with an electronically conjugated bridge, resulting in the first SVLA CuI PSs (Cu-2 and Cu-3). Cu-3 has an extremely high molar extinction coefficient of 162 260 m?1 cm?1 at 518 nm, over 62 times higher than that of traditional CuI PS (Cu-1). The photooxidation activity of Cu-3 is much greater than that of Cu-1 and noble-metal PSs (Ru(bpy)32+ and Ir(ppy)3+) for both energy- and electron-transfer reactions. Femto- and nanosecond transient absorption and theoretical investigations demonstrate that a “ping-pong” energy-transfer process in Cu-3 involving a forward singlet TBET from Bodipy to the CuI complex and a backward triplet-triplet energy transfer greatly contribute to the long-lived and Bodipy-localized triplet excited state.
- Chen, Kai-Kai,Guo, Song,Li, Xiyou,Liu, Heyuan,Lu, Tong-Bu,Zhang, Zhi-Ming
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- One-Pot Preparation of Tricyclo[5.2.2.04,9]undecanes via Cu-Catalyzed Asymmetric Carboboration of Cyclohexadienone-Tethered Allenes
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The Cu-catalyzed asymmetric carboboration of cyclohexadienone-tethered allenes has been achieved through regioselective β-borylation of the allenes and subsequent conjugate addition to cyclohexadienones, affording cis-bicyclic frameworks with acceptable yields and high to excellent enantioselectivities. Further conjugate borylation of the carboboration products proved to be a favorable kinetic resolution process, which improved the overall enantioselectivity. Finally, one-pot preparation of highly enantioenriched tricyclo[5.2.2.04,9]undecanes was developed from the cyclohexadienone-tethered allenes through β-borylation/1,4-addition and subsequent tandem oxidation/intramolecular aldol reaction.
- Feng, Kai-Rui,Tan, Yun-Xuan,Ye, Wenbo,Wang, Yi-Fan,He, Zhi-Tao,Tian, Ping,Lin, Guo-Qiang
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- Catalytic activity of the anaerobic tyrosine lyase required for thiamine biosynthesis in Escherichia coli
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Thiazole synthase in Escherichia coli is an αβ heterodimer of ThiG and ThiH. ThiH is a tyrosine lyase that cleaves the Cα-Cβ bond of tyrosine, generating p-cresol as a by-product, to form dehydroglycine. This reactive intermediate acts as one of three substrates for the thiazole cyclization reaction catalyzed by ThiG. ThiH is a radical S-adenosylmethionine (AdoMet) enzyme that utilizes a [4Fe-4S]+ cluster to reductively cleave AdoMet, forming methionine and a 5′-deoxyadenosyl radical. Analysis of the time-dependent formation of the reaction products 5′- deoxyadenosine (DOA) and p-cresol has demonstrated catalytic behavior of the tyrosine lyase. The kinetics of product formation showed a pre-steady state burst phase, and the involvement of DOA in product inhibition was identified by the addition of 5′-methylthioadenosine/S-adenosylhomocysteine nucleosidase to activity assays. This hydrolyzed the DOA and changed the rate-determining step but, in addition, substantially increased the uncoupled turnover of AdoMet. Addition of glyoxylate and ammonium inhibited the tyrosine cleavage reaction, but the reductive cleavage of AdoMet continued in an uncoupled manner. Tyrosine analogues were incubated with ThiGH, which showed a strong preference for phenolic substrates. 4-Hydroxyphenylpropionic acid analogues allowed uncoupled AdoMet cleavage but did not result in further reaction (Cα-Cβ bond cleavage). The results of the substrate analogue studies and the product inhibition can be explained by a mechanistic hypothesis involving two reaction pathways, a product-forming pathway and a futile cycle.
- Challand, Martin R.,Martins, Filipa T.,Roach, Peter L.
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- Kinetics of the Thermal Decomposition of Methoxybenzene (Anisole)
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The thermal decomposition of anisole vapor dilute in argon has been studied in a perfectly stirred reactor over the temperature range 850-1000 K and at total pressures of (16-120)E-3 atm.Decomposition of anisole takes place principally by the reaction C6H
- Mackie, J. C.,Doolan, K. R.,Nelson, P. F.
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- Cresol Izomerization in the Presence of Acid Catalysts
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It is shown for toluene oxidation with nitrous oxide that modifying HZSM-5 zeolite with zinc oxide nanoparticles considerably improves the selectivity and yield of cresols. It is found that a 2% ZnO/HZSM-5 composite catalyst also exhibits enhanced and stable activity at high temperatures. For the o-cresol isomerization reaction, this modification of HZSM-5 zeolite greatly reduces the contribution from disproportionation and cracking reactions proceeding with formation of phenol, C6–C9 aromatic hydrocarbons, and xylenols. The regularities of their formation in the presence of the studied catalysts are determined using the results from thermodynamic calculations for the equilibrium concentrations of cresol isomers.
- Tarasov,Dunaev,Kustov
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- A green approach for phenol synthesis over Fe3+/MgO catalysts using hydrogen peroxide
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An efficient green route for the synthesis of phenol from benzene has been reported over Fe3+/MgO catalysts under mild conditions. Fe3+/MgO catalysts are prepared and well characterized using EDX, XRD, FTIR, surface area analysis pore volume determination and UV-vis diffuse reflectance studies. Activity of these systems towards single step oxidation of benzene to phenol at low temperature using H2O2 has been analyzed. The catalysts exhibited interesting oxidizing ability which has been attributed to Fe(III) dispersed in amorphous form as isolated units on MgO. Possibility of homogeneous nature of catalysis through leached Fe3+ ions has been ruled out by confirming the absence of Fe3+ in liquid phase, and the heterogeneous nature of catalysis has been confirmed. The decomposition of H2O2 by the catalysts has been studied. Reusability of the system is assured carrying out multiple runs using the recycled catalyst. The activity has been analysed towards reactants with various substituents in benzene ring. A metalloperoxide formation on the surface of MgO through heterolytic cleavage of H2O2 has also been suggested for the reaction.
- Renuka
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- MCM-41-supported phosphotungstic acid-catalyzed cleavage of C-O bond in allyl aryl ethers
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Removal of the protecting allyl group from allyl aryl ethers in the presence of other oxygen protecting groups was successfully achieved using a solid acid supported on the high surface area material MCM-41. The catalyst showed excellent activity in the presence of various electron withdrawing, electron donating, and oxidizable functional groups. The methodology is also very useful for the removal of protecting allyl groups of various natural products such as vanillin, isovanillin, and other oxygen functionalized aldehydes and ketones.
- Sakate, Sachin S.,Kamble, Sumit B.,Chikate, Rajeev C.,Rode, Chandrashekhar V.
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- Base-free oxidative homocoupling of arylboronic esters
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Base-free oxidative homocoupling reaction of arylboronic esters has been found to proceed using a catalytic amount of a palladium-1,3-bis(diphenylphosphino)propane (DPPP) complex under an oxygen atmosphere, affording a variety of biaryls in modest to excellent yields. Even arylboronic esters bearing a base-sensitive functional group are applicable to the reaction.
- Yoshida, Hiroto,Yamaryo, Yasuhito,Ohshita, Joji,Kunai, Atsutaka
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- Nickel-catalyzed cross-coupling of aryl grignard reagents with aromatic alkyl ethers: An efficient synthesis of unsymmetrical biaryls
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New substrates for biaryl synthesis: aromatic ethers undergo nickel-catalyzed cross-coupling with aryl Grignard reagents to give unsymmetrical biaryls in excellent yields (see scheme). Both the nature of the nickel catalyst and the choice of solvent are crucial for reaching high levels of conversion.
- Dankwardt, John W.
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- Electrophilic Aromatic Substitution. Part 28. The Mechanism of Nitration of Some 4-Substituted Anisoles and Phenols, and of Rearrangement of the Intermediate 4-Nitro-4-substituted-cyclohexa-2,5-dienones
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The kinetics of nitration in sulphuric acid of 2-chloro-4-methyl-, 4-chloro-, 2,4-dichloro-, and 4-fluoroanisole and of the corresponding phenols have been determined.The reaction products from the anisoles and from 2-chloro-4-methyl- and 4-fluoro-phenol have been determined.Results for 4-methylanisole supplementary to earlier ones are also reported.Generally the anisoles give the 2-nitro-derivatives and the 2-nitrophenols, and from 2-chloro-4-methylanisole, 2-chloro-4-methyl-4-nitrocyclohexa-2,5-dienone was formed as an intermediate.The decomposition of this dienone in sulphuric acid, like those of others, changes from a non-acid-catalysed to an acid-catalysed form with increasing acidity.The first form is regarded as a decomposition into an aryloxyl radical and nitrogen dioxide which can recombine to give the 2-nitrophenol.The formation of a small amount of 2-(4-fluorophenoxy)-4-fluorophenol in the nitration of 4-fluorophenol is seen as support for this view.The acid-catalysed form is regarded as the decomposition of the protonated dienone into a phenol-nitronium ion encounter-pair which can give the nitrophenol.A consequence of the mechanism is that if the phenol were nitrated at less than the encounter rate, the phenol itself would in appropriate conditions be a product of the ipso-nitration of the original anisole. 4-Methyl-, 2-chloro-4-methyl-, and 4-chloro-phenol have been so identified.Quantitative analysis of the results allows evaluation of the partitioning of dienone decomposition between the two modes.The mechanism accounts for the formation from 2,4-dichloro-anisole of both 2,4-dichloro-6- and 2,4-dichloro-5-nitroanisole, but only 2,4-dichloro-6-nitrophenol.
- Bloomfield, Colin,Manglik, Ajay K.,Moodie, Roy B.,Schofield, Kenneth,Tobin, Geoffrey D.
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- Effects of ascorbic acid on arenediazonium salts reactivity: Kinetics and mechanism of the reaction
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We have examined the kinetics and mechanism of dediazoniation of o-, m- and p-methylbenzenediazonium (ArN2-) tetrafluoroborate in the presence of ascorbic acid (H2A) at different pHs by combining spectophotometric (VIS-UV), high performance liquid chromatography (HPLC), and polarographic measurements. Kinetic data show that, at low pH, observed rate constants increase linearly with increasing ascorbic acid concentration, but the saturation kinetics observed at higher pH suggest the formation of a transient diazo-ether complex preceding the slow step of the reaction. Experimental evidence for the formation of such a complex was obtained from a competitive coupling reaction with the Na salt of '2-naphthol-6-sulfonic acid' and by titration of ascorbic acid (H2A) with the arenediazonium ions (electrochemical measurements). HPLC Analysis of dediazoniation products indicates that, in the absence of H2A, only the heterolytic phenol derivative, ArOH, is formed quantitatively, in keeping with the predictions of the DN+AN mechanism. In the pH 2-4 range and in the presence of H2A, reduction products (ArH) are obtained in addition to heterolytic products (ArOH), corroborating that certain biological reducing agents like ascorbate (HA-) are capable of inducing reductive fragmentation of ArN2- into aryl radicals. All evidence is consistent with two competitive reaction pathways, the thermal decomposition of ArN2+, and a rate-limiting decomposition of the transient diazo ether 'complex', formed during the reaction of ArN2+ with HA- in a rapid pre-equilibrium step.
- Costas-Costas, Ugo,Gonzalez-Romero, Elisa,Bravo-Diaz, Carlos
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- Liquid-phase oxidation of alkyl-substituted cyclohexylbenzenes
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The reactivity of alkyl-substituted cyclohexylbenzenes in liquid-phase oxidation was estimated by the k2/√k6 value which considerably decreased as the number of methyl groups in the substrate molecule increased. The observed difference in the reactivity of the title compounds was attributed to the degree of coplanarity of intermediate radical species.
- Koshel',Kurganova,Smirnova,Koshel',Plakhtinskii,Belysheva
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- A MODEL FOR METABOLIC ACTIVATION OF DIALKYLNITROSAMINES. OXIDATIVE DEALKYLATION OF N-NITROSO-2-(ALKYLAMINO)ACETONITRILE BY FLAVIN MIMIC IN AQUEOUS SOLUTION
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Oxidation-active flavin mimic, benzodipteridine (BDP), is found to react with N-nitroso-2-(alkylamino)acetonitrile via oxidative dealkylation in aqueous solution.From the kinetic investigations, the oxidation mechanism is proposed.
- Yano, Yumihiko,Yokoyama, Takeshi,Yoshida, Kitaro
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- BORON TETRAHALIDE-METHYL SULFIDE COMPLEXES AS CONVENIENT REAGENTS FOR DEALKYLATION OF ARYL ETHERS
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High yield dealkylation of several aryl methyl ethers was observed upon exposure of these compounds to an excess of the boron trihalidemethyl sulfide complexes.
- Williard, Paul G.,Fryhle, Craig B.
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- Comparison of neurotoxic effects and potential risks from oral administration or ingestion of tricresyl phosphate and jet engine oil containing tricresyl phosphate
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Neurotoxicity of tricresyl phosphates (TCPs) and jet engine oil (JEO) containing TCPs were evaluated in studies conducted in both rat and hen. Results for currently produced samples ('conventional' and 'low-toxicity') were compared with published findings on older samples to identify compositional changes and relate those changes to neurotoxic potential. Finally, a human risk assessment for exposure by oral ingestion of currently produced TCPs in JEO at 3% (JEO + 3%) was conducted. TCPs and certain other triaryl phosphates administered as single doses inhibited brain neuropathy target esterase (B-NTE; neurotoxic esterase) in the rat and the hen (hen 3.25 times as sensitive), and both species were deemed acceptable for initial screening purposes. Neither rat nor hen was sensitive enough to detect statistically significant inhibition of B-NTE after single doses of JEO + 3% 'conventional' TCP. Subacute administration of 2 g/kg/d of JEO + 3% 'conventional' TCP to the hen produced B-NTE inhibition 132%), which did not result in organophosphorus-induced delayed neurotoxicity (OPIDN). Subchronic administration of JEO + 3% TCP but not JEO + 1% TCP at 2 g/kg/d produced OPIDN. Thus, the threshold for OPIDN was between 20 and 60 mg 'conventional' TCP/kg/d in JEO for 10 wk. The current 'conventional' TCPs used in JEO and new 'low-toxicity' TCPs now used in some JEO are synthesized from phenolic mixtures having reduced levels of ortho-cresol and ortho-xylenols resulting in TCPs of very high content of meta- and para-substituted phenyl moieties; this change in composition results in lower toxicity. The 'conventional' TCPs still retain enough inhibitory activity to produce OPIDN, largely because of the presence of ortho-xylyl moieties; the 'low-toxicity' TCPs are largely devoid of ortho substituents and have extremely low potential to cause OPIDN. The TCP produced in the 1940s and 1950s were more than 400 times as toxic as the 'low-toxicity' TCPs produced today. Analysis of the doses required to produce OPIDN in a subchronic hen study suggests that the minimum toxic dose of 'conventional' TCP for producing OPIDN in a 70-kg person would be 280 mg/d, and for JEO containing 3% TCP, 9.4 g/d. Food products could be inadvertently contaminated with neat 'conventional' TCP but it is unlikely that food such as cooking oil would be contaminated with enough JEO + 3% TCP to cause toxicity. Further, at the dosage required for neurotoxiciy, it would be virtually impossible for a person to receive enough JEO + 3% TCP in the normal workplace (or in an aircraft) to cause such toxicity. There is no record of a JEO formulated with the modern 'conventional' TCP causing human neurotoxicity.
- Mackerer, Carl R.,Barth, Mary L.,Krueger, Andrew J.,Chawla, Birbal,Roy, Timothy A.
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- Topology-guided design of an anionic bor-network for photocatalytic [Ru(bpy)3]2+ encapsulation
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An anionic metal-organic framework, PCN-99, has been synthesized through a topology-guided strategy; its underlying bor-net is realized by the use of a tetrahedral [In(COO)4]- node and a judiciously designed trigonal planar linker. In light of its anionic nature, the inherent cuboctahedral cage and 1D channel make PCN-99 an excellent matrix to encapsulate the photocatalytic [Ru(bpy)3]2+.
- Wang, Xuan,Lu, Weigang,Gu, Zhi-Yuan,Wei, Zhangwen,Zhou, Hong-Cai
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- Retentive Solvolysis. 15. Salt Effect ion the Retentive Phenolyses of 1-(p-Substituted phenyl)ethyl p-Nitrobenzoates. The Pattern of Salt Effect and the Number of Ion-Pair Intermediates in the SN1 Solvolysis
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The salt effect of sodium phenoxide on the polarimetric (kp) and titrimetric rate constants (kt) has exhibited pattern B for the phenolysis of optically active 1-(p-methylphenyl)ethyl p-nitrobenzoate (ROPNB; (1)) in pure phenol.The other patterns A, C, and D were previously observed for the phenolyses of 1-phenylethyl p-nitrobenzoates with p-MeO- (2), p-H- (3), and p-NO2-substituents (4), respectively.Thus, the kp-kt pattern changes in the order A -> B -> C -> D as the stability of the intermediate decreases in the order of 2 > 1 > 3 > 4.All the kp-kt patterns can be correlated with the ion-pair stage for product formation, i.e., the pattern A with the second ion-pair intermediate and the patterns B, C, and D with the first one.The pattern of salt effect on the product distribution (percent of ROPh, o- and p-RC6H4OH, and p-MeC6H4CH=CH2) for 1 is also compatible with the kp-kt pattern B.
- Kinoshita, Tomomi,Shibayama, Koichi,Ikai, Keizo,Okamoto, Kunio
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- Cationic Polycarbazole Networks as Visible-Light Heterogeneous Photocatalysts for Oxidative Organic Transformations
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Photoredox catalysis has aroused great interest from chemists, as it offers a powerful tool for organic synthesis. Cationic polycarbazole networks (CPOP-28 and CPOP-29) were prepared via simple oxidative coupling reaction and applied as heterogeneous photocatalysts for a wide range of oxidative organic transformations, including oxidation of sulfides, hydroxylation of arylboronic acids, and cross-dehydrogenative coupling reactions, in the presence of visible light and air. Remarkably, photocatalytic activities are enhanced by ingenious introduction of trifluoromethyl groups to the polymeric network CPOP-29. The effects of the trifluoromethyl group on photocatalytic activities were elucidated in terms of photophysical and electrochemical properties. The appealing photocatalytic performance of the trifluoromethylated polymer is ascribed to superior light-absorption ability, longer fluorescence lifetime, and stronger oxidative capability. In addition, the photocatalysts showed good recyclability and could be reused after a simple separation workup.
- Liang, Hai-Peng,Chen, Qi,Han, Bao-Hang
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- One-pot synthesis of cresols from toluene and hydroxylamine catalyzed by ammonium molybdate
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One-pot synthesis of cresols from toluene and hydroxylamine catalyzed by ammonium molybdate was investigated under mild conditions. The hydroxylation reaction was strongly dependent on reaction medium, temperature, the amount of catalyst and hydroxylamine. Moreover, the reaction took place more efficiently in a closed system than in open air. High toluene conversion (72.9%) and cresol selectivity (79.4%) were obtained at 80 °C in water-acetic acid-sulfuric acid medium.
- Zhang, Dongsheng,Gao, Liya,Wang, Yanji,Xue, Wei,Zhao, Xinqiang,Wang, Shufang
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- Geminate Recombination Kinetics of Triplet Radical Pairs in Glycerol: Magnetic Field Effect
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Laser flash technique has been used to record the geminate recombination kinetics of triplet radical pairs (RP) generated from benzophenone photoreduced with p-cresol in the viscous glycerol/p-cresol binary solvent.The RP decay kinetics fits fairly into the first-order law.At the same time the kinetics curve features a manifest slow descending "tail" that follows the φinfinite-φ(t) ca. t-1/2 relationship, where φinfinite is the (total) cage effect and φ(t) is the time-dependent cage effect.The geminate recombination kinetics is closely described in the entire time range (0 10 μs) by the function originating from Noyes' treatment of molecular dynamics, φ(t) = φinfinite erfc (kNt-1/2) where kN is a constant.An increse of solvent viscosity (decrease of temperature) causes an increase of φinfinite and deceleration of RP dissociation.The geminate recombination kinetics is described by mutual diffusion coefficients smaller than the sum of the diffusion coefficients of individual radicals.The probable reason of such behavior is that there is a strong correlation between the molecular motions of radicals positioned within several molecular diameters from each other.Application of an external magnetic field (H infinite by 10-50percent.The extent of the magnetic effect heavily depends on H when H0.1 T and is practically independent of H when 0.1H 0.1 T, the magnetic field acts by the hfc mechanism and by slowing the paramagnetic relaxation due to the hfc anisotropy and dipole-dipole coupling between unpaired electrons.
- Levin, Peter P.,Khudyakov, Igor V.,Kuzmin, Vladimir A.
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- Efficient hydroxylation of aromatic compounds catalyzed by an iron(II) complex with H2O2
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A mononuclear iron(II) complex, Et4N[Fe(C10H 6NO2)3], coordinated by three 1-nitroso-2-naphtholate ligands in a fac-N3O3 geometry, was initiated to catalyze the direct hydroxylation of aromatic compounds to phenols in the presence of H2O2 under mild conditions. Various reaction parameters, including the catalyst dosage, temperature, mole ratio of H2O2 to benzene, reaction time and solvents which could affect the hydroxylation activity of the catalyst, were investigated systematically for benzene hydroxylation to obtain ideal benzene conversion and high phenol distribution. Under the optimum conditions, the benzene conversion was 10.2% and only phenol was detected. The catalyst was also found to be active towards hydroxylation of other aromatic compounds with high substrate conversions. The hydroxyl radical formed due to the reaction of the catalyst and H2O2 was determined to be the crucial active intermediate in the hydroxylation. A rational pathway for the formation of the hydroxyl radical was proposed and justified by the density functional theory calculations. Copyright
- Wang, Xiao,Zhang, Tianyong,Li, Bin,Yang, Qiusheng,Jiang, Shuang
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- Reactions of 4-Benzoyl-4-methylcyclohexa-2,5-dienone in Acids: Retro-Fries Rearrangements
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4-Benzoyl-4-methylcyclohexa-2,5-dienone is known as one of the few relatively stable 4-acylcyclohexa-2,5-dienones.In attempts to achieve dienone-phenol rearrangements with acyl migration it has been treated with Lewis acids and with non-nucleophilic acids in non-polar solvents.In each case rapid acil migration occurs to give 4-methylphenyl benzoate by a retro-Fries rearrangement, along with some cleavage to the phenol.The benzoyl group can be trapped by another phenol, and the mechanism is formulated as a dissociation-recombination process with significant leakage of the 4-methylphenol and benzoyl cation.The reaction is compared with the Fries/retro-Fries equilibrium which has been induced between phenyl esters and 2- and 4-acyl phenols.Observations are made on the photochemical Fries rearrangement of 4-methylphenyl acetate, which has been suggested to proceed via 4-acetyl-4-methylcyclohexa-2,5-dienone, and of 4-methylphenyl benzoate.
- Jackson, Lorraine B.,Waring, Anthony J.
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- Mn2(CO)10-Catalyzed Intramolecular Dimerization of Diphosphirane Complexes
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In this report, a series of biphosphirane complexes 1 were synthesized from the phosphiranide complex. The binuclear Mn2(CO)10-catalyzed intramolecular dimerization of these biphosphirane complexes provided 1,4-diphosphanorbornane derivatives. This work demonstrates the synthetic possibility of transforming small phosphiranes to phospha-heterocycles by metal-catalyzed reactions.
- Wang, Min,Qiu, Lingzhi,Cui, Mingyue,Tian, Rongqiang,Duan, Zheng,Mathey, Fran?ois
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- Visible-Light Photoredox Borylation of Aryl Halides and Subsequent Aerobic Oxidative Hydroxylation
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Efficient and practical visible-light photoredox borylation of aryl halides and subsequent aerobic oxidative hydroxylation were developed. The protocols use readily available aryl halides and bis(pinacolato)diboron as the starting materials, fac-Ir(ppy)3 as the photocatalyst, and corresponding arylboronic esters and phenols were obtained in good yields. The methods show some advantages including simple equipment, mild conditions, easy operation, and wide substrate scope. Therefore, they should provide a valuable strategy for chemical transformations.
- Jiang, Min,Yang, Haijun,Fu, Hua
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- Arene-ruthenium(II)-phosphine complexes: Green catalysts for hydration of nitriles under mild conditions
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Three new arene-ruthenium(II) complexes were prepared by treating [{RuCl(μ-Cl)(η6-arene)}2] (η6-arene = p-cymene) dimer with tri(2-furyl)phosphine (PFu3) and 1,3,5-triaza-7-phosphaadamantane (PTA), respectively to obtain [RuCl2(η6-arene)PFu3] [Ru]-1, [RuCl(η6-arene)(PFu3)(PTA)]BF4 [Ru]-2 and [RuCl(η6-arene)(PFu3)2]BF4 [Ru]-3. All the complexes were structurally identified using analytical and spectroscopic methods including single-crystal X-ray studies. The effectiveness of resulting complexes as potential homogeneous catalysts for selective hydration of different nitriles into corresponding amides in aqueous medium and air atmosphere was explored. There was a remarkable difference in catalytic activity of the catalysts depending on the nature and number of phosphorus-donor ligands and sites available for catalysis. Experimental studies performed using structural analogues of efficient catalyst concluded a structural-activity relationship for the higher catalytic activity of [Ru]-1, being able to convert huge variety of aromatic, heteroaromatic and aliphatic nitriles. The use of eco-friendly water as a solvent, open atmosphere and avoidance of any organic solvent during the catalytic reactions prove the reported process to be truly green and sustainable.
- Vyas, Komal M.,Mandal, Poulami,Singh, Rinky,Mobin, Shaikh M.,Mukhopadhyay, Suman
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- The complex synergy of water in metal/bromide autoxidations. Part II. Effect of water and catalyst on the aerobic oxidation of benzaldehydes and the effect of water on the elementary catalytic pathways
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All of the rates of the elementary steps in the Co/Br and Co/Mn/Br homogeneous, liquid-phase catalyzed reactions decrease with increasing water concentration in acetic acid. The step-wise replacement of the acetic acid ligands by water ligands in the coordination sphere of the catalyst metals may be responsible for this behavior. The non-catalyzed and metal-catalyzed (Co, Co/Mn/Br and Co/Mn) aerobic oxidations of benzaldehyde and 4-methylbenzaldehyde are reported. The non-catalyzed autoxidations are quite vigorous reactions in acetic acid/water mixtures but by-products from the Baeyer-Villiger reaction, the thermal decomposition of the peroxy acid, and over-oxidation to carbon dioxide limit the yield to the aromatic carboxylic acids. As the concentration of a Co or Co/Mn/Br catalyst increases these by-products are first reduced and then eliminated probably due to the very fast, selective reaction of [Co(II)]2 with the peroxy acid. A Co/Mn catalyst completely inhibits the autoxidation of the benzaldehydes. There is a gradual change in the yield of terephthaldicarboxaldehyde from 4-methylbenzaldehyde with increasing Co/Mn/Br concentration suggesting that the non-catalyzed steps are being replaced by catalyzed ones. The autoxidation of heptaldehyde generates about 500 times more carbon monoxide than does benzaldehyde using a Co/Mn/Br catalyst and gives only a 50% yield to heptanoic acid consistent with excessive amounts of decarbonylation with aliphatic aldehydes.
- Partenheimer, Walt
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- Effects of salt, acid and base on the decomposition of 2-chlorophenol in supercritical water
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The effect of salt, acid and base as additives on the decomposition of 2-chlorophenol (2CP) in supercritical water was investigated. Four additives were selected, NaCl as a salt, HCl and H2SO4 as acids, and KOH as a base. The addition of salts and acids had a little effect on the decomposition of 2CP in supercritical water (SCW), but that of bases showed a significant effect to enhance the decomposition rate.
- Lee, Geun-Hee,Nunoura, Teppei,Matsumura, Yukihiko,Yamamoto, Kazuo
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- Catalytic cleavage of ether C-O bonds by pincer iridium complexes
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The development of efficient catalytic methods to cleave the relatively unreactive C-O bonds of ethers remains an important challenge in catalysis. Building on our group's recent work, we report the dehydroaryloxylation of aryl alkyl ethers using pincer iridium catalysts. This method represents a rare fully atom-economical method for ether C-O bond cleavage.
- Haibach, Michael C.,Lease, Nicholas,Goldman, Alan S.
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- Catalytic Activation of Unstrained C(Aryl)-C(Alkyl) Bonds in 2,2′-Methylenediphenols
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Catalytic activation of unstrained and nonpolar C-C bonds remains a largely unmet challenge. Here, we describe our detailed efforts in developing a rhodium-catalyzed hydrogenolysis of unstrained C(aryl)-C(alkyl) bonds in 2,2′-methylenediphenols aided by removable directing groups. Good yields of the monophenol products are obtained with tolerating a wide range of functional groups. In addition, the reaction is scalable, and the catalyst loading can be reduced to as low as 0.5 mol %. Moreover, this method proves to be effective to cleave C(aryl)-C(alkyl) linkages in both models of phenolic resins and commercial novolacs resins. Finally, detailed experimental and computational mechanistic studies show that with C-H activation being a competitive but reversible off-cycle reaction, this transformation goes through a directed C(aryl)-C(alkyl) oxidative addition pathway.
- Dong, Guangbin,Ratchford, Benjamin L.,Xue, Yibin,Zhang, Rui,Zhu, Jun
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supporting information
p. 3242 - 3249
(2022/02/23)
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- REARRANGEMENT OF DIMETHYLPHENYLACYLATES USING ZEOLITES
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The present invention relates to a Fries rearrangement of specific dimethylphenylacylates to form the desired respective hydroxyaryl ketones having two methyl groups bound to the aromatic ring. It has been found that the process is surprisingly very specific in view of the number and position of the methyl group(s) bound to the aromatic ring.
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Page/Page column 9-10; 15
(2021/08/14)
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- Metal-Organic Framework-Confined Single-Site Base-Metal Catalyst for Chemoselective Hydrodeoxygenation of Carbonyls and Alcohols
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Chemoselective deoxygenation of carbonyls and alcohols using hydrogen by heterogeneous base-metal catalysts is crucial for the sustainable production of fine chemicals and biofuels. We report an aluminum metal-organic framework (DUT-5) node support cobalt(II) hydride, which is a highly chemoselective and recyclable heterogeneous catalyst for deoxygenation of a range of aromatic and aliphatic ketones, aldehydes, and primary and secondary alcohols, including biomass-derived substrates under 1 bar H2. The single-site cobalt catalyst (DUT-5-CoH) was easily prepared by postsynthetic metalation of the secondary building units (SBUs) of DUT-5 with CoCl2 followed by the reaction of NaEt3BH. X-ray photoelectron spectroscopy and X-ray absorption near-edge spectroscopy (XANES) indicated the presence of CoII and AlIII centers in DUT-5-CoH and DUT-5-Co after catalysis. The coordination environment of the cobalt center of DUT-5-Co before and after catalysis was established by extended X-ray fine structure spectroscopy (EXAFS) and density functional theory. The kinetic and computational data suggest reversible carbonyl coordination to cobalt preceding the turnover-limiting step, which involves 1,2-insertion of the coordinated carbonyl into the cobalt-hydride bond. The unique coordination environment of the cobalt ion ligated by oxo-nodes within the porous framework and the rate independency on the pressure of H2 allow the deoxygenation reactions chemoselectively under ambient hydrogen pressure.
- Antil, Neha,Kumar, Ajay,Akhtar, Naved,Newar, Rajashree,Begum, Wahida,Manna, Kuntal
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supporting information
p. 9029 - 9039
(2021/06/28)
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- A mild and practical method for deprotection of aryl methyl/benzyl/allyl ethers with HPPh2andtBuOK
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A general method for the demethylation, debenzylation, and deallylation of aryl ethers using HPPh2andtBuOK is reported. The reaction features mild and metal-free reaction conditions, broad substrate scope, good functional group compatibility, and high chemical selectivity towards aryl ethers over aliphatic structures. Notably, this approach is competent to selectively deprotect the allyl or benzyl group, making it a general and practical method in organic synthesis.
- Pan, Wenjing,Li, Chenchen,Zhu, Haoyin,Li, Fangfang,Li, Tao,Zhao, Wanxiang
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p. 7633 - 7640
(2021/09/22)
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- Highly selective demethylation of anisole to phenol over H4Nb2O7modified MoS2catalyst
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Hydrogenolysis of lignin to obtain value-added phenolic chemicals is an important approach for its comprehensive utilization. Herein, H4Nb2O7modified MoS2catalyst with short slabs and narrow stacking degree was successfully synthesized by the one step hydrothermal method and used in the selective demethylation of anisole to phenol. The MoS2-H4Nb2O7-160 catalyst exhibited the best activity with 97.7% conversion of anisole and 98.0% selectivity of phenol under 3 MPa H2pressure at 270 °C for 4 h, which has been rarely reported on anisole transformation over heterogeneous catalysts so far. The characterizations results demonstrated that the H4Nb2O7modification reduced the slab length and stacking degree of MoS2during the hydrothermal process and enhanced the acidity property therefore improved the cleavage ability of CArO-CH3bond. This study provides a new scheme for the activity enhancement of MoS2in lignin demethylation, laying a foundation on the improvement of lignin utilization and the development of renewable energy strategy.
- Ji, Na,Wang, Zhenjiao,Diao, Xinyong,Jia, Zhichao,Li, Tingting,Zhao, Yujun,Liu, Qingling,Lu, Xuebin,Ma, Degang,Song, Chunfeng
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p. 800 - 809
(2021/02/26)
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- Aromatic C?H Hydroxylation Reactions with Hydrogen Peroxide Catalyzed by Bulky Manganese Complexes
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The oxidation of aromatic substrates to phenols with H2O2 as a benign oxidant remains an ongoing challenge in synthetic chemistry. Herein, we successfully achieved to catalyze aromatic C?H bond oxidations using a series of biologically inspired manganese catalysts in fluorinated alcohol solvents. While introduction of bulky substituents into the ligand structure of the catalyst favors aromatic C?H oxidations in alkylbenzenes, oxidation occurs at the benzylic position with ligands bearing electron-rich substituents. Therefore, the nature of the ligand is key in controlling the chemoselectivity of these Mn-catalyzed C?H oxidations. We show that introduction of bulky groups into the ligand prevents catalyst inhibition through phenolate-binding, consequently providing higher catalytic turnover numbers for phenol formation. Furthermore, employing halogenated carboxylic acids in the presence of bulky catalysts provides enhanced catalytic activities, which can be attributed to their low pKa values that reduces catalyst inhibition by phenolate protonation as well as to their electron-withdrawing character that makes the manganese oxo species a more electrophilic oxidant. Moreover, to the best of our knowledge, the new system can accomplish the oxidation of alkylbenzenes with the highest yields so far reported for homogeneous arene hydroxylation catalysts. Overall our data provide a proof-of-concept of how Mn(II)/H2O2/RCO2H oxidation systems are easily tunable by means of the solvent, carboxylic acid additive, and steric demand of the ligand. The chemo- and site-selectivity patterns of the current system, a negligible KIE, the observation of an NIH-shift, and the effectiveness of using tBuOOH as oxidant overall suggest that hydroxylation of aromatic C?H bonds proceeds through a metal-based mechanism, with no significant involvement of hydroxyl radicals, and via an arene oxide intermediate. (Figure presented.).
- Masferrer-Rius, Eduard,Borrell, Margarida,Lutz, Martin,Costas, Miquel,Klein Gebbink, Robertus J. M.
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p. 3783 - 3795
(2021/03/09)
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- Ceria-promoted Co@NC catalyst for biofuel upgrade: synergy between ceria and cobalt species
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Ceria-promoted Co@NC (NC, N doped carbon) catalysts are prepared by pyrolysis of biomass materials. Characterization results indicate that ceria and Co species facilitate the distribution of each other due to the formation of a Ce-O-Co solid solution. The specific surface area of the catalyst increased from 378.77 to 537.7 m2g?1viathe introduction of ceria. The electron transfer from Co to Ce further enhanced their interaction, and Co species facilitate the formation of more defective oxygen vacancies on ceria, which are beneficial to the activities of catalytic hydrogenation and catalytic transfer hydrogenation (CTH), respectively. Thus, Co/Ce@NC (0.99% Co loading) pyrolyzed at 850 °C exhibits excellent performance in the hydrodeoxygenation (HDO) of vanillin with high metal utilization. Catalytic hydrogenation and CTH coexisted in the presence of H2and ethanol, and >99% yield of creosol can be obtained in each of them. The reaction processes are monitored. No intermediate is found in aqueous media, while ethoxymethyl-4-methoxy-2-phenol is detected in ethanol. Moreover, Co/Ce@NC presents outstanding stability and general applicability. This work provides new insights into the construction of M@NC (M, metal) catalysts and the HDO process of biofuel upgrade.
- Wang, Bowei,Gao, Ruixiao,Zhang, Dan,Zeng, Yuyao,Zhang, Fangying,Yan, Xilong,Li, Yang,Chen, Ligong
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supporting information
p. 8541 - 8553
(2021/04/12)
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- Encapsulated Ni-Co alloy nanoparticles as efficient catalyst for hydrodeoxygenation of biomass derivatives in water
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Catalytic hydrodeoxygenation (HDO) is one of the most promising strategies to transform oxygen-rich biomass derivatives into high value-added chemicals and fuels, but highly challenging due to the lack of highly efficient nonprecious metal catalysts. Herein, we report for the first time of a facile synthetic approach to controllably fabricate well-defined Ni-Co alloy NPs confined on the tip of N-CNTs as HDO catalyst. The resultant Ni-Co alloy catalyst possesses outstanding HDO performance towards biomass-derived vanillin into 2-methoxy-4-methylphenol in water with 100% conversion efficiency and selectivity under mild reaction conditions, surpassing the reported high performance nonprecious HDO catalysts. Impressively, our experimental results also unveil that the Ni-Co alloy catalyst can be generically applied to catalyze HDO of vanillin derivatives and other aromatic aldehydes in water with 100% conversion efficiency and over 90% selectivity. Importantly, our DFT calculations and experimental results confirm that the achieved outstanding HDO catalytic performance is due to the greatly promoted selective adsorption and activation of C=O, and desorption of the activated hydrogen species by the synergism of the alloyed Ni-Co NPs. The findings of this work affords a new strategy to design and develop efficient transition metal-based catalysts for HDO reactions in water.
- Chen, Chun,Gong, Wanbing,Han, Miaomiao,Wang, Dongdong,Wang, Guozhong,Zhang, Haimin,Zhang, Jifang,Zhang, Yunxia,Zhao, Huijun
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p. 2027 - 2037
(2021/09/02)
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- Selective upgrading of biomass-derived benzylic ketones by (formic acid)–Pd/HPC–NH2 system with high efficiency under ambient conditions
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Upgrading biomass-derived phenolic compounds provides a valuable approach for the production of higher-value-added fuels and chemicals. However, most established catalytic systems display low hydrodeoxygenation (HDO) activities even under harsh reaction conditions. Here, we found that Pd supported on –NH2-modified hierarchically porous carbon (Pd/HPC–NH2) with formic acid (FA) as hydrogen source exhibits unprecedented performance for the selective HDO of benzylic ketones from crude lignin-derived oxygenates. Designed experiments and theoretical calculations reveal that the H+/H? species generated from FA decomposition accelerates nucleophilic attack on carbonyl carbon in benzylic ketones and the formate species formed via the esterification of intermediate alcohol with FA expedites the cleavage of C–O bonds, achieving a TOF of 152.5 h?1 at 30°C for vanillin upgrading, 15 times higher than that in traditional HDO processes (~10 h?1, 100°C–300°C). This work provides an intriguing green route to produce transportation fuels or valuable chemicals from only biomass under mild conditions.
- Chen, Yuzhuo,Chen, Zhirong,Gong, Yutong,Mao, Shanjun,Ning, Honghui,Wang, Yong,Wang, Zhenzhen
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p. 3069 - 3084
(2021/11/16)
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- Aryl phenol compound as well as synthesis method and application thereof
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The invention discloses a synthesis method of an aryl phenol compound shown as a formula (3). All systems are carried out in an air or nitrogen atmosphere, and visible light is utilized to excite a photosensitizer for catalyzation. In a reaction solvent, ArNR1R2 as shown in a formula (1) and water as shown in a formula (2) are used as reaction raw materials and react under the auxiliary action of acid to obtain the aryl phenol compound as shown in a formula (3). The ArNR1R2 in the formula (1) can be primary amine and tertiary amine, can also be steroid and amino acid derivatives, and can also be drugs or derivatives of propofol, paracetamol, ibuprofen, oxaprozin, indomethacin and the like. The synthesis method has the advantages of cheap and easily available raw materials, simple reaction operation, mild reaction conditions, high reaction yield and good compatibility of substrate functional groups. The fluid reaction not only can realize amplification of basic chemicals, but also can realize amplification of fine chemicals, such as synthesis of drugs propofol and paracetamol. The invention has wide application prospect and use value.
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Paragraph 0046-0049
(2021/05/12)
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- A mild desilylation of phenolic tert-butyldimethylsilyl ethers using in situ generated tetraethylammonium superoxide
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Desilylation of phenolic tert-butyldimethylsilyl ethers has been achieved under the mild reaction conditions of in situ generated tetraethylammonium superoxide, at room temperature. (Figure presented.).
- Pandey, Surabhi,Shukla, Ajay K.,Raghuvanshi, Raghvendra S.
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p. 809 - 811
(2021/07/16)
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- Electrochemical-induced hydroxylation of aryl halides in the presence of Et3N in water
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A thorough study of mild and environmentally friendly electrochemical-induced hydroxylation of aryl halides without a catalyst is presented. The best protocol consists of hydroxylation of different aryl iodides and aryl bromides by water solution in the presence of Et3N under air, affording the target phenols in good isolated yields. Moreover, aryl chlorides were successfully employed as substrates. This methodology also provides a direct pathway for the formation of deoxyphomalone, which displayed a significant anti-proliferation effect.
- Ke, Fang,Lin, Chen,Lin, Mei,Long, Hua,Wu, Mei,Yang, Li,Zhuang, Qinglong
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supporting information
p. 6417 - 6421
(2021/08/03)
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- Photocatalytic synthesis of phenols mediated by visible light using KI as catalyst
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A transition-metal-free hydroxylation of iodoarenes to afford substituted phenols is described. The reaction is promoted by KI under white LED light irradiation and uses atmospheric oxygen as oxidant. By the use of triethylamine as base and solvent, the corresponding phenols are obtained in moderate to good yields. Mechanistic studies suggest that KI and catalysis synergistically promote the cleavage of C-I bond to form free aryl radicals.
- Huiqin, Wei,Wu, Mei
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supporting information
(2021/11/30)
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- Visible light-induced photodeoxygenation of polycyclic selenophene Se-oxides
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Photodeoxygenation of dibenzothiophene S-oxide (DBTO) is believed to produce ground-state atomic oxygen [O(3P)] in solution. Compared with other reactive oxygen species (ROS), O(3P) is a unique oxidant as it is potent and selective. Derivatives of DBTO have been used as O(3P)-precursors to oxidize variety of molecules, including plasmid DNA, proteins, lipids, thiols, and other small organic molecules. Unfortunately, the photodeoxygenation of DBTO requires ultraviolet irradiation, which is not an ideal wavelength range for biological systems, and has a low quantum yield of approximately 0.003. In this work, benzo[b]naphtho[1,2-d]selenophene Se-oxide, benzo[b]naphtho[2,1-d]selenophene Se-oxide, dinaphtho[2,3-b:2’,3’-d]selenophene Se-oxide, and perylo[1,12-b,c,d]selenophene Se-oxide were synthesized, and their ability to utilize visible light for generating O(3P) was interrogated. Benzo[b]naphtho[1,2-d]selenophene Se-oxide produces O(3P) upon irradiation centered at 420 nm. Additionally, benzo[b]naphtho[1,2-d]selenophene Se-oxide, benzo[b]naphtho[2,1-d]selenophene Se-oxide, and dinaphtho[2,3-b:2’,3’-d]selenophene Se-oxide produce O(3P) when irradiated with UVA light and have quantum yields of photodeoxygenation ranging from 0.009 to 0.33. This work increases the utility of photodeoxygenation by extending the range of wavelengths that can be used to generate O(3P) in solution.
- Chintala, Satyanarayana M.,Throgmorton, John C.,Maness, Peter F.,McCulla, Ryan D.
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- Catalyst-free rapid conversion of arylboronic acids to phenols under green condition
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A catalyst-free and solvent-free method for the oxidative hydroxylation of aryl boronic acids to corresponding phenols with hydrogen peroxide as the oxidizing agent was developed. The reactions could be performed under green condition at room temperature within very short reaction time. 99% yield of phenol could be achieved in only 1 min. A series of different arenes substituted aryl boronic acids were further carried out in the hydroxylation reaction with excellent yield. It was worth nothing that the reaction could completed within 1 min in all cases in the presence of ethanol as co-solvent.
- Dong, Zhenhua,Liu, Mengmeng,Pan, Hongguo
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- Isotruxene-based porous polymers as efficient and recyclable photocatalysts for visible-light induced metal-free oxidative organic transformations
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Two new isotruxene-based porous polymers were prepared and demonstrated to be highly efficient, metal-free heterogeneous photocatalysts for oxidative transformations using air as the mild oxidant under visible-light irradiation. Both catalysts show excellent recyclability. In addition, the reactions can be performed in water, further indicating the greenness of this method. This journal is
- Zhang, Haowen,Zhang, Xiao,Zheng, Ying,Zhou, Cen
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supporting information
p. 8878 - 8885
(2021/11/27)
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- Coordination Polymers as a Functional Material for the Selective Molecular Recognition of Nitroaromatics and ipso-Hydroxylation of Arylboronic Acids
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We report the synthesis and structural characterization of two coordination polymers (CPs), namely; [{Zn(L)(DMF)4} ? 2BF4]α (1) and [{Cd(L)2(Cl)2} ? 2H2O]α (2) (where L=N2,N6-di(pyridin-4-yl)naphthalene-2,6-dicarboxamide). Crystal packing of 1 reveals the existence of channels running along the b- and c-axis filled by the ligated DMF and lattice anions, respectively. Whereas, crystal packing of 2 reveals that the metallacycles of each 1D chain are intercalating into the groove of adjacent metallacycles resulting in the stacking of 1D loop-chains to form a sheet-like architecture. In addition, both 1 and 2 were exploited as multifunctional materials for the detection of nitroaromatic compounds (NACs) as well as a catalyst in the ipso-hydroxylation of aryl/heteroarylboronic acids. Remarkably, 1 and 2 showed high fluorescence stability in an aqueous medium and displayed a maximum 88% and 97% quenching efficiency for 4-NPH, respectively among all the investigated NACs. The mechanistic investigation of NACs recognition suggested that the fluorescence quenching occurred via electron as well as energy transfer process. Furthermore, the ipso-hydroxylation of aryl/heteroarylboronic acids in presence of 1 and 2 gave up to 99% desired product yield within 15 min in our established protocol. In both cases, 1 and 2 are recyclable upto five cycles without any significant loss in their efficiency.
- Bhasin, K. K.,Husain, Ahmad,Kumar, Girijesh,Rani, Pooja
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- Cu2O/TiO2 as a sustainable and recyclable photocatalyst for gram-scale synthesis of phenols in water
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A green and straightforward protocol was developed for the synthesis of phenols from aryl boronic acid using an inexpensive and available Cu2O/TiO2 photocatalyst under visible light and sunlight. This approach proceeded in mild reaction conditions in water and the presence of air as a green oxidant, resulting in the corresponding phenols in good to excellent yields. Sunlight was also a sustainable source for this photochemical reaction. Heterogeneous nano photocatalyst was successfully recovered in 8 consecutive runs. It is noteworthy that, the photocatalyst exhibited high activity for the large-scale synthesis of phenols.
- Hosseini-Sarvari, Mona,Keshavarz, Kimia,Tavakolian, Mina
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- Highly efficient heterogeneous V2O5@TiO2 catalyzed the rapid transformation of boronic acids to phenols
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A V2O5@TiO2 catalyzed green and efficient protocol for the hydroxylation of boronic acid into phenol has been developed utilizing environmentally benign oxidant hydrogen peroxide. A wide range of electron-donating and the electron-withdrawing group-containing (hetero)aryl boronic acids were transformed into their corresponding phenol. The methodology was also applied successfully to transform various natural and bioactive molecules like tocopherol, amino acids, cinchonidine, vasicinone, menthol, and pharmaceuticals such as ciprofloxacin, ibuprofen, and paracetamol. The other feature of the methodology includes gram-scale synthetic applicability, recyclability, and short reaction time.
- Upadhyay, Rahul,Singh, Deepak,Maurya, Sushil K.
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supporting information
p. 3925 - 3931
(2021/08/24)
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- Highly efficient, recyclable and alternative method of synthesizing phenols from phenylboronic acids using non-endangered metal: Samarium oxide
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Oxidation of phenylboronic acid to phenol is one of the important industrial processes and it is generally employed in the plastic, explosive and drug manufacturing industries. Over the past decades, numerous efficient methods have been described for the generation of phenols from phenylboronic acids in the presence of oxidant. However, these methods suffered from various limitations, including the use of expensive, toxic reagents and sophisticated protocol to synthesise the phenols. Additionally, some of these reported literatures employed endangered metals, in which mankind is facing the risk of limited supply of these elements in 20 years’ time from now. As such, a viable alternative and green method for achieving organic synthesis is highly sought after by the chemists of today. Herein, we report for the first time a facile, efficient and alternative method in the preparation of phenols from phenylboronic acids using non-endangered metal as catalyst. In all cases, all phenols were afforded in satisfactory yields (81–96%) by employing column-free method. In the recyclability study, the Sm2O3 catalyst was found to possess good catalytic performance, even after being reused for five consecutive times (96–91%). In addition, SEM result revealed that the morphology of the recycled Sm2O3 catalyst was well preserved after five successive uses, which indicate no observable changes occurred in the recovered catalysts. As a final note, the current method is anticipated to be useful for industries manufacturing chemical intermediates as it provides an alternative method of catalysis by using a non-endangered metal in organic transformations.
- Yusoff, Hanis Mohd,Bala Chandran, Prasana Devi,Sayuti, Fatin Amira Binti,Kan, Su-Yin,Mohd Radzi, Siti Aisha,Yong, Fu-Siong Julius,Lee, Oon Jew,Chia, Poh Wai
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- Double Insurance of Continuous Band Structure and N-C Layer Induced Prolonging of Carrier Lifetime to Enhance the Long-Wavelength Visible-Light Catalytic Activity of N-Doped In2O3
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Nonmetallic doped metal oxides can be broad in their visible-light-response range. However, the half-filled or isolated impurity state can also be the new recombination center for photogenerated electrons/holes, which seriously influence the photocatalytic activity of the catalyst in the visible-light region. Therefore, how to prolong the photogenerated carrier life of nonmetallic doping metal oxides is the difficult and challenging topic in the field of photocatalysis. In this work, the hexagonal nanosheets assembled by N-doped C (N-C)-coated N-doped In2O3 (N-In2O3) nanoparticles (N-C/N-In2O3 HS) was obtained by simply pyrolyzing the In(2,5-PDC) hexagonal sheets. The N-C/N-In2O3 HS catalyst exhibit good photocatalytic activity and cycle stability in the long-wavelength region of visible light (λ = 520 and 595 nm). The effective utilization of long-wavelength visible light for N-C/N-In2O3 HS was mainly attributed to the acceptor-donor-acceptor compensation mechanism between the oxygen vacancy (VO) and substitutional N-doping (Ns) sites, which made the N-C/N-In2O3 HS possess a continuous band structure, without the half-filled or isolated impurity state in the band gap, and extended its light absorption edge to 733 nm. The compensation mechanism of nitrogen doping on In2O3 can promote the photocatalytic activity under longer-wavelength yellow light (595 nm) irradiation. The N-C layer coated on the N-In2O3 nanoparticles acted as a good acceptor of photogenerated electrons, facilitating the effective spatial separation of photogenerated carriers and extend photogenerated carrier lifetimes. The comparative photocatalytic experiments (N-In2O3 HS and N-C/N-In2O3 HS) show that the presence of N-doped C layer can enhance the photocatalytic efficiency by nearly 10-fold. This double-doping and carbon-coating strategy provided a novel research idea to solve the problem that nonmetal atoms doped metal oxides led to the secondary combination of photogenerated electrons/holes.
- Sun, Liming,He, Xiaoxiao,Zeng, Suyuan,Yuan, Yusheng,Li, Rong,Zhan, Wenwen,Chen, Jinquan,Wang, Xiaojun,Han, Xiguang
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supporting information
p. 1160 - 1171
(2021/01/18)
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- Application of Electron-Rich Covalent Organic Frameworks COF-JLU25 for Photocatalytic Aerobic Oxidative Hydroxylation of Arylboronic Acids to Phenols
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Visible-light-driven organic reactions are environmentally friendly green chemical transformations among which photosynthetic oxidative hydroxylation of arylboronic acids to phenols has attracted increasing research interest during the very recent years. Given the efficiency and reusability of heterogeneous catalysts, COF-JLU25, an electron-rich COF-based photocatalyst constructed by integrating electron-donating blocks 1,3,6,8-tetrakis(4-aminophenyl)pyrene (PyTA) and 4-[4-(4-formylmethyl)-2,5-dimethoxyphenyl] benzaldehyde (TpDA), was selected as a photocatalyst for the oxidative hydroxylation of arylboronic acids. In our studies, COF-JLU25 demonstrated excellent photocatalytic activity with high efficiency, robust reusability, and low catalyst loading, showcasing an application potential of previously underexplored COF-based photocatalyst composed solely of electron-rich units.
- Xiao, Guangjun,Li, Wenqian,Chen, Tao,Hu, Wei-Bo,Yang, Hui,Liu, Yahu A.,Wen, Ke
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supporting information
p. 3986 - 3991
(2021/03/29)
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- Transforming a Fluorochrome to an Efficient Photocatalyst for Oxidative Hydroxylation: A Supramolecular Dimerization Strategy Based on Host-Enhanced Charge Transfer
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The development of non-covalent synthetic strategy to fabricate efficient photocatalysts is of great importance in theranostic and organic materials. Herein, a fluorochrome N,N′-dimethyl 2,5-bis(4-pyridinium)thiazolo[5,4-d]thiazolediiodide (MPT) was transformed into an efficient photocatalyst through supramolecular dimerization in the cavity of cucurbit[8]uril (CB[8]). The host-enhanced charge transfer interaction within the supramolecular dimer 2MPT-CB[8] dramatically promoted intersystem crossing to produce triplet. In addition, the staggered conformation of 2MPT-CB[8] facilitated the energy transfer and electron transfer of the triplet. As a result, 2MPT-CB[8] could serve as a high-efficiency photocatalyst for the oxidative hydroxylation of arylboronic acids. This supramolecular dimerization strategy enriches the supramolecular engineering of functional π-systems. It is anticipated that this strategy can be extended to fabricate various π-systems with tailor-made functions.
- Tang, Bohan,Xu, Weiquan,Xu, Jiang-Fei,Zhang, Xi
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supporting information
p. 9384 - 9388
(2021/03/22)
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- Blacklight-Induced Hydroxylation of Arylboronic Acids Leading to Hydroxyarenes Using Molecular Oxygen and Tetrabutylammonium Borohydride
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A new simple protocol for the conversion of arylboronic acids to hydroxyarenes was achieved using molecular oxygen in the presence of tetrabutylammonium borohydride under blacklight irradiation (360 nm). A radical chain mechanism in which a superoxide ion (O2?.) plays a key role is proposed.
- Kawamoto, Takuji,Ryu, Ilhyong
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- Photocatalytic Activity of Ruthenium(II) Complex with 1,10-Phenanthroline-3,8-dicarboxylic Acid in Aerobic Oxidation Reactions
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Abstract: Mixed-ligand ruthenium(II) complex with 2,2′-bipyridine and 1,10-phenanthroline-3,8-dicarboxylic acid with the composition [Ru(phen-C)(bpy)2]Cl2·5H2O (bpy = 2,2′-bipyridine, phen-C = 1,10-phenantroline-3,8-dicarboxylic acid) has been synthesized and characterized by spectral data. The complex has been tested as photocatalyst in aerobic oxidation reactions, including transformation of arylboronic acids to phenols, primary amines to imines, and sulfides to sulfoxides in aqueous medium. The possibility of regeneration of the catalyst in the oxidation of sulfides has been demonstrated.
- Abel, A. S.,Averin, A. D.,Beletskaya, I. P.,Bessmertnykh-Lemeune, A. G.,Yakushev, A. A.,Zenkov, I. S.
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p. 1398 - 1404
(2021/10/26)
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- Ligand compound for copper catalyzed aryl halide coupling reaction, catalytic system and coupling reaction
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The invention provides a ligand compound capable of being used for copper catalyzed aryl halide coupling reaction, the ligand compound is a three-class compound containing a 2-(substituted or non-substituted) aminopyridine nitrogen-oxygen group, and the invention also provides a catalytic system for the aryl halide coupling reaction. Thecatalytic system comprises a copper catalyst, a compound containing a 2-(substituted or non-substituted) aminopyridine nitrogen-oxygen group adopted as a ligand, alkali and a solvent, and meanwhile, the invention also provides a system for the aryl halide coupling reaction adopting the catalyst system. The compound containing the 2-(substituted or non-substituted) aminopyridine nitrogen oxygen group can be used as the ligand for the copper catalyzed aryl chloride coupling reaction, and the ligand is stable under a strong alkaline condition and can well maintain catalytic activity when being used for the copper-catalyzed aryl chloride coupling reaction. In addition, the copper catalyst adopting the compound as the ligand can particularly effectively promote coupling of copper catalyzed aryl chloride and various nucleophilic reagents which are difficult to generate under conventional conditions, C-N, C-O and C-S bonds are generated, and numerous useful small molecule compounds are synthesized. Therefore, the aryl halide coupling reaction has a very good large-scale application prospect by adopting the copper catalysis system of the ligand.
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Paragraph 0152-0158
(2021/05/29)
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- Crystal Facet Engineering of Copper-Based Metal-Organic Frameworks with Inorganic Modulators
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Manipulating the exposed facets of metal-organic frameworks (MOFs) is of importance toward understanding their facet-dependent property in a variety of applications. Herein, we apply a novel inorganic competitive coordination strategy to control the growth orientation of copper-based MOFs (HKUST-1, MOF-14, and Cu-MOF-74) without sacrificing the pore accessibility and crystallinity. Through monitoring the reactant composition, we find that the competitive coordination induced by the added aluminium nitrate mainly affects the crystal growth stage rather than the nucleation stage. The kinetic study further reveals that Al3+ competes with Cu2+ to coordinate with ligands, restraining the growth rate of certain facets and resulting in the orientated growth of copper-based MOFs. Compared to the reduced pore accessibility of HKUST-1 crystals modulated by the organic modulation method, Al3+-modulated HKUST-1 displays a much larger surface area (>2200 m2/g) and more accessible Cu active sites. Hydroxylation of toluene was utilized as a model reaction to investigate the facet-catalytic activity for as-synthesized HKUST-1. The selectivity of the preferred product cresol increases with the morphology transformation of HKUST-1 from octahedron to cube.
- Wang, Zhanke,Ge, Lei,Feng, Desheng,Jiang, Zongrui,Wang, Hao,Li, Mengran,Lin, Rijia,Zhu, Zhonghua
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p. 926 - 934
(2021/01/26)
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- A copper nitride catalyst for the efficient hydroxylation of aryl halides under ligand-free conditions
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Copper nitride (Cu3N) was used as a heterogeneous catalyst for the hydroxylation of aryl halides under ligand-free conditions. The cubic Cu3N nanoparticles showed high catalytic activity, comparable to those of conventional Cu catalysts with nitrogen ligands, demonstrating that the nitrogen atoms in Cu3N act as functional ligands that promote hydroxylation.
- Mitsudome, Takato,Mizugaki, Tomoo,Xu, Hang,Yamaguchi, Sho
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supporting information
p. 6593 - 6597
(2021/08/10)
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- Selective hydroxylation of aryl iodides to produce phenols under mild conditions using a supported copper catalyst
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Owing to the high activity and low-cost, copper-based catalysts are promising candidates for transforming aromatic halides to yield phenols. In this work, we report the selective hydroxylation of aromatic iodides to produce phenols using an atomically dispersed copper catalyst (Cu-ZnO-ZrO2) under mild reaction conditions. The reactions were conducted without the use of additional organic ligands, and the protection of an inert atmosphere environment is not required. The catalyst can be easily prepared, scalable, and is very efficient for a wide range of substrates. The catalytic reactions can be carried out with only 1.24 mol% Cu loading, which shows great potential in mass production.
- Auni, Anika,Ding, Guodong,Hao, Leiduan,Li, Tao,Li, Xiaoyu,Xu, Haiping,Zhang, Qiang
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p. 25348 - 25353
(2021/08/03)
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- Decarboxylative Hydroxylation of Benzoic Acids
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Herein, we report the first decarboxylative hydroxylation to synthesize phenols from benzoic acids at 35 °C via photoinduced ligand-to-metal charge transfer (LMCT)-enabled radical decarboxylative carbometalation. The aromatic decarboxylative hydroxylation is synthetically promising due to its mild conditions, broad substrate scope, and late-stage applications.
- Ritter, Tobias,Su, Wanqi,Xu, Peng
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p. 24012 - 24017
(2021/10/06)
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- Eco-friendly preparation of ultrathin biomass-derived Ni3S2-doped carbon nanosheets for selective hydrogenolysis of lignin model compounds in the absence of hydrogen
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Lignin is an abundant source of aromatics, and the depolymerization of lignin provides significant potential for producing high-value chemicals. Selective hydrogenolysis of the C-O ether bond in lignin is an important strategy for the production of fuels and chemical feedstocks. In our study, catalytic hydrogenolysis of lignin model compounds (β-O-4, α-O-4 and 4-O-5 model compounds) over Ni3S2-CS catalysts was investigated. Hence, an array of 2D carbon nanostructure Ni3S2-CSs-X-Yderived catalysts were produced using different compositions at different temperatures (X= 0 mg, 0.2 mg, 0.4 mg, 0.6 mg, and 0.8 mg; Y = 600 °C, 700 °C, 800 °C, and 900 °C) were prepared and applied for hydrogenolysis of lignin model compounds and depolymerization of alkaline lignin. The highest conversion of lignin model compounds (β-O-4 model compound) was up to 100% and the yield of the obtained corresponding ethylbenzene and phenol could achieve 92% and 86%, respectively, over the optimal Ni3S2-CSs-0.4-700 catalyst in iPrOH at 260 °C without external H2. The 2D carbon nanostructure catalysts performed a good dispersion on the surface of the carbon nanosheets, which facilitated the cleavage of the lignin ether bonds. The physicochemical characterization studies were carried out by means of XRD, SEM, TEM, H2-TPR, NH3-TPD, Raman and XPS analyses. Based on the optimal reaction conditions (260 °C, 4 h, 2.0 MPa N2), various model compounds (β-O-4, α-O-4 and 4-O-5 model compounds) could also be effectively hydrotreated to produce the corresponding aromatic products. Furthermore, the optimal Ni3S2-CSs-0.4-700 catalyst could be carried out in the next five consecutive cycle experiments with a slight decrease in the transformation of lignin model compounds.
- Chen, Changzhou,Jiang, Jianchun,Li, Jing,Liu, Peng,Wu, Dichao,Xia, Haihong,Zhou, Minghao
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p. 3090 - 3103
(2021/05/07)
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- Rhodium(III)-Catalyzed Asymmetric Reductive Cyclization of Cyclohexadienone-Containing 1,6-Dienes via an Anti-Michael/Michael Cascade Process
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Ring strain plays an important role in metal-catalyzed cyclization of 1,6-dienes. Herein, we report a rhodium(III)-catalyzed asymmetric reductive cyclization of cyclohexadienone-tethered α,β-unsaturated compounds (1,6-dienes), including α,β-unsaturated ketones, esters, amides, sulfone, and phosphonate. The reactions undergo an unusual anti-Michael/Michael addition process, affording cis-bicyclic frameworks with good to high yields and good diastereo- and enantioselectivities. Furthermore, several transformations of the products and a one-pot preparation of bridged polycyclic structure are also presented. Finally, DFT calculations show that the enantioselectivity is determined by the initial olefin insertion step and that the ring strain controls the overall regioselectivity and favors the formation of 5,6-bicyclic products.
- Ding, Rui,Hong, Xin,Li, Qing-Hua,Liao, Qi,Lin, Guo-Qiang,Tan, Yun-Xuan,Tian, Ping,Wang, Yu-Hui,Xie, Pei-Pei,Xu, Hao,Zhang, Jian-Wei
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p. 8015 - 8022
(2021/07/13)
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- Substituent and Surfactant Effects on the Photochemical Reaction of Some Aryl Benzoates in Micellar Green Environment?
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In this study, we carried out preparative and mechanistic studies on the photochemical reaction of a series of p-substituted phenyl benzoates in confined and sustainable micellar environment. The aim of this work is mainly focused to show whether the nature of the surfactant (ionic or nonionic) leads to noticeable selectivity in the photoproduct formation and whether the electronic effects of the substituents affect the chemical yields and the rate of formation of the 5-substituted-2-hydroxybenzophenone derivatives. Application of the Hammett linear free energy relationship (LFER) on the rate of formation of benzophenone derivatives, on the lower energy band of the UV-visible absorption spectra of the aryl benzoates and 5-substituted-2-hydroxybenzophenone derivatives allows a satisfactory quantification of the substituent effects. Furthermore, UV-visible and 2D-NMR (NOESY) spectroscopies have been employed to measure the binding constant Kb and the location of the aryl benzoates within the hydrophobic core of the micelle. Finally, TD-DFT calculations have been carried out to estimate the energies of the absorption bands of p-substituted phenyl benzoates and 5-substituted-2-hydroxybenzophenone derivatives providing good linear correlation with those values measured experimentally.
- Siano, Gastón,Crespi, Stefano,Bonesi, Sergio M.
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p. 1298 - 1309
(2021/05/07)
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- Separation of Anisole and Valuable Byproducts from Liquid Reaction Mixtures by Solvent Extraction and Multicomponent Distillation
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Anisole (methoxybenzene) is a widely used organic intermediate that can be synthesized via vapor-phase alkylation of phenol by methanol in the presence of a commercial NaX zeolite as a catalyst (SiO2:Al2O3 ratio of 2.6:3). The indigenously synthesized anisole is then separated from the multicomponent liquid reaction mixture, consisting of o-cresol, p-cresol and p-xylen, along with unreacted methanol and phenol. The separated anisole has substantial demand for applications in the chemical, pharmaceutical, plastics and pesticides industries. Separation of individual components from the reaction mixture requires identification of techniques that could be scaled up. Distillation is one of the most dependable techniques for the separation of multicomponent liquid mixtures. The novelty of the present study is the synthesis and separation of anisole along with individual components of methanol, phenol and o-cresol from its reaction mixture using a single distillation column under atmospheric and vacuum conditions, respectively. Through this process, the purity of the resulting methanol, anisole and phenol were found to be 99.99, 99.80 and 98.29% by simple distillation, whereas 91.0% pure o-cresol was separated by vacuum distillation due to its high boiling point. The experimental results were used to calculate the material, individual component and energy balances, whereas the PRO/II process simulation was performed to scale-up the process. On the other hand, anisole recovery from a synthetic multicomponent liquid mixture was also successfully conducted using solvent extraction. The overall observations found the integration of solvent extraction with distillation to be an effective, economical and dependable solution for the isolation of anisole and other important by-products.
- Vani, Bukke,Pabba, Manideep,Kalyani, Swayampakula,Sridhar, Sundergopal
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p. 160 - 177
(2021/01/29)
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- Method for synthesizing heteroatom- substituted aromatic compound from styrene compound
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The invention discloses a method for synthesizing a heteroatom-substituted aromatic compound from a styrene compound, which comprises the following steps of: mixing a styrene compound with a general formula (I) and a heteroatom-containing compound with a general formula (II), and reacting in the presence of an acid additive and an organic solvent to obtain a heteroatom-substituted compound with ageneral formula (III). According to the synthesis method disclosed by the invention, a large amount of styrene compounds are used as raw materials and react to generate aromatic amine or phenol compounds under the action of no metal catalysis; and compared with the traditional aromatic amine and phenol synthesis method, the method has the advantages of high yield, simple conditions, low waste discharge amount, no metal participation, simple reaction equipment, easiness in industrial production and the like.
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-
Paragraph 0334-0337
(2021/02/06)
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- Catalytic C–O bond cleavage in a β-O-4 lignin model through intermolecular hydrogen transfer
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A base-free and redox neutral approach for the selective breaking of aryl ether bond (C–O) contained by a lignin model compound mimicking a β-O-4 linkage is reported. A palladium loaded metal-organic framework (MOF) was used as a catalyst for this purpose. The reaction proceeds through dehydrogenation of benzylic alcohol moiety followed by the hydrogenolysis of the ether bonds. Therefore, no external hydrogen source is required for the reaction to take place.
- Ahsan Usman, Muhammad,Naeem, Maham,Saeed, Muhammad,Zaheer, Muhammad
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- Photo-induced thiolate catalytic activation of inert Caryl-hetero bonds for radical borylation
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Substantial effort is currently being devoted to obtaining photoredox catalysts with high redox power. Yet, it remains challenging to apply the currently established methods to the activation of bonds with high bond dissociation energy and to substrates with high reduction potentials. Herein, we introduce a novel photocatalytic strategy for the activation of inert substituted arenes for aryl borylation by using thiolate as a catalyst. This catalytic system exhibits strong reducing ability and engages non-activated Caryl–F, Caryl–X, Caryl–O, Caryl–N, and Caryl–S bonds in productive radical borylation reactions, thus expanding the available aryl radical precursor scope. Despite its high reducing power, the method has a broad substrate scope and good functional-group tolerance. Spectroscopic investigations and control experiments suggest the formation of a charge-transfer complex as the key step to activate the substrates.
- K?nig, Burkhard,Wang, Hua,Wang, Shun
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supporting information
p. 1653 - 1665
(2021/06/17)
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- Alkylsulfenyl thiocarbonates: precursors to hydropersulfides potently attenuate oxidative stress
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The recent discovery of the prevalence of hydropersulfides (RSSH) species in biological systems suggests their potential roles in cell regulatory processes. However, the reactive and transient nature of RSSH makes their study difficult, and dependent on the use of donor molecules. Herein, we report alkylsulfenyl thiocarbonates as a new class of RSSH precursors that efficiently release RSSH under physiologically relevant conditions. RSSH release kinetics from these precursors are tunable through electronic modification of the thiocarbonate carbonyl group's electrophilicity. In addition, these precursors also react with thiols to release RSSH with a minor amount of carbonyl sulfide (COS). Importantly, RSSH generation by these precursors protects against oxidative stress in H9c2 cardiac myoblasts. Furthermore, we demonstrate the ability of these precursors to increase intracellular RSSH levels.
- Aggarwal, Sahil C.,Khodade, Vinayak S.,Paolocci, Nazareno,Pharoah, Blaze M.,Toscano, John P.
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p. 8252 - 8259
(2021/06/22)
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- CATALYTIC FUNNELING OF PHENOLICS
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In general, present invention concerns an integrated wood-to-xylochemicals biorefinery, enabling production of renewable phenol, phenolic oligomers, propylene, and carbohydrate pulp from lignocellulosic biomass.
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-
Paragraph 0034; 0089-0090; 0167-0168
(2021/04/30)
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- Catalytic SNAr Hydroxylation and Alkoxylation of Aryl Fluorides
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Nucleophilic aromatic substitution (SNAr) is a powerful strategy for incorporating a heteroatom into an aromatic ring by displacement of a leaving group with a nucleophile, but this method is limited to electron-deficient arenes. We have now established a reliable method for accessing phenols and phenyl alkyl ethers via catalytic SNAr reactions. The method is applicable to a broad array of electron-rich and neutral aryl fluorides, which are inert under classical SNAr conditions. Although the mechanism of SNAr reactions involving metal arene complexes is hypothesized to involve a stepwise pathway (addition followed by elimination), experimental data that support this hypothesis is still under exploration. Mechanistic studies and DFT calculations suggest either a stepwise or stepwise-like energy profile. Notably, we isolated a rhodium η5-cyclohexadienyl complex intermediate with an sp3-hybridized carbon bearing both a nucleophile and a leaving group.
- Kang, Qi-Kai,Li, Ke,Li, Yuntong,Lin, Yunzhi,Shi, Hang,Xu, Lun
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supporting information
p. 20391 - 20399
(2021/08/13)
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- Diastereo- And enantioselective rhodium(iii)-catalyzed reductive cyclization of cyclohexadienone-containing 1,6-dienes
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A diastereo- and enantioselective rhodium(iii)-catalyzed reductive cyclization of cyclohexadienone-tethered terminal alkenes and (E)-1,2-disubstituted alkenes (1,6-dienes) is reported, providingcis-bicyclic products bearing three contiguous stereocenters with good yields and high diastereo- and enantioselectivities. The kinetic resolution of the racemic precursor is also achieved with good efficiency. Moreover, a subgram-scale experiment, several transformations of the cyclization product, and one-pot preparation of bridged polycyclic frameworks are presented.
- Gao, Dingding,Lin, Guo-Qiang,Liu, Xi-Liang,Peng, Pei-Ying,Tan, Yun-Xuan,Tian, Ping,Wang, Ya-Jie,Ye, Wenbo
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supporting information
p. 9724 - 9727
(2021/09/30)
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- Reaction of hydroxyl radical with arenes in solution—On the importance of benzylic hydrogen abstraction
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The regioselectivity of hydroxyl radical reactions with alkylarenes was investigated using a nuclear magnetic resonance (NMR)-based methodology capable of trapping and quantifying addition and hydrogen abstraction products of the initial elementary step of the oxidation process. Abstraction products are relatively minor components of the product mixtures (15–30 mol%), depending on the magnitude of the overall rate coefficient and the number of available hydrogens. The relative reactivity of addition at a given position on the ring depends on its relation to the methyl substituents on the hydrocarbons under study. The reactivity enhancements for disubstituted and trisubstituted rings are approximately additive under the conditions of this study.
- Waggoner, Abygail R.,Abdulrahman, Yahya,Iverson, Alexis J.,Gibson, Ethan P.,Buckles, Mark A.,Poole, James S.
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- Cleavage∕cross-coupling strategy for converting β-O-4 linkage lignin model compounds into high valued benzyl amines via dual C–O bond cleavage
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Lignin is the most recalcitrant of the three components of lignocellulosic biomass. The strength and stability of the linkages have long been a great challenge for the degradation and valorization of lignin biomass to obtain bio-fuels and commercial chemicals. Up to now, the selective cleavage of C–O linkages of lignin to afford chemicals contains only C, H and O atoms. Our group has developed a cleavage/cross-coupling strategy for converting 4-O-5 linkage lignin model compounds into high value-added compounds. Herein, we present a palladium-catalyzed cleavage/cross-coupling of the β-O-4 lignin model compounds with amines via dual C–O bond cleavage for the preparation of benzyl amine compounds and phenols.
- Jia, Le,Li, Chao-Jun,Zeng, Huiying
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supporting information
(2021/10/29)
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- Hydrosilylation of Esters Catalyzed by Bisphosphine Manganese(I) Complex: Selective Transformation of Esters to Alcohols
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Selective and efficient hydrosilylations of esters to alcohols by a well-defined manganese(I) complex with a commercially available bisphosphine ligand are described. These reactions are easy alternatives for stoichiometric hydride reduction or hydrogenation, and employing cheap, abundant, and nonprecious metal is attractive. The hydrosilylations were performed at 100 °C under solvent-free conditions with low catalyst loading. A large variety of aromatic, aliphatic, and cyclic esters bearing different functional groups were selectively converted into the corresponding alcohols in good yields.
- Bagh, Bidraha,Behera, Rakesh R.,Ghosh, Rahul,Khamari, Subrat,Panda, Surajit
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supporting information
p. 3642 - 3648
(2020/04/20)
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- Mechanistic study of carboxylic acid and phosphate ester cleavage by oximate metal complexes surpassing the limiting reactivity of highly basic free oximate anions
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Two tridentate and one tetradentate new ligands containing the terminal oxime group separated from secondary amino and pyridine groups as additional binding sites by two or three methylene groups have been prepared. Their acid-base properties, as well as the composition and stability of their complexes with Zn(ii) and Cd(ii) ions, were determined by potentiometric and spectrophotometric titrations. The X-ray structure of a Cd(ii) complex of a related tridentate oxime ligand previously studied in solution was determined. All oximate complexes show high reactivity in the cleavage of aryl acetates, paraoxon, parathion and 4-nitrophenyl diphenyl phosphate, with rate constants significantly surpassing the limiting rate constants observed for highly basic free oximate anions. The second-order rate constants for individual oximate complexes in solution are assigned to each ligand, metal cation and substrate. The results of the cleavage of 4-substituted phenyl acetates were analyzed in terms of Br?nsted correlations with the leaving group pKa, which demonstrated a change in the rate determining step from the nucleophilic attack to the leaving group departure upon an increase in the leaving group basicity. The zero slope of the Br?nsted correlation for the nucleophilic attack indicates transition state stabilization through electrophilic assistance by the metal ion. This interpretation is supported by metal selectivity in the relative efficiency of the cleavage of paraoxon and parathion. The existence of the alpha-effect in ester cleavage by coordinated oximates is confirmed by an analysis of the Br?nsted correlations with the nucleophile basicity for metal bound oximate and alkoxo or hydroxo nucleophiles. The very high reactivity of the oximate complexes of the new ligands is attributed to transition state stabilization and to the removal of the solvational imbalance of oximate anions that impedes the expected increase in the reactivity of highly basic free anions.
- Flores-Alamo, Marcos,Gómez-Tagle, Paola,Lugo-González, José Carlos,Yatsimirsky, Anatoly K.
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supporting information
p. 2452 - 2467
(2020/03/05)
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- Cu(i) complexes obtained: Via spontaneous reduction of Cu(ii) complexes supported by designed bidentate ligands: Bioinspired Cu(i) based catalysts for aromatic hydroxylation
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Copper(i) complexes [Cu(L1-7)2](ClO4) (1-7) of bidentate ligands (L1-L7) have been synthesized via spontaneous reduction and characterized as catalysts for aromatic C-H activation using H2O2 as the oxidant. The single crystal X-ray structure of 1 exhibited a distorted tetrahedral geometry. All the copper(i) complexes catalyzed direct hydroxylation of benzene to form phenol with good selectivity up to 98%. The determined kinetic isotope effect (KIE) values, 1.69-1.71, support the involvement of a radical type mechanism. The isotope-labeling experiments using H218O2 showed 92% incorporation of 18O into phenol and confirm that H2O2 is the key oxygen supplier. Overall, the catalytic efficiencies of the complexes are strongly influenced by the electronic and steric factor of the ligand, which is fine-tuned by the ligand architecture. The benzene hydroxylation reaction possibly proceeded via a radical mechanism, which was confirmed by the addition of radical scavengers (TEMPO) to the catalytic reaction that showed a reduction in phenol formation. This journal is
- Kumari, Sheela,Muthuramalingam, Sethuraman,Dhara, Ashish Kumar,Singh,Mayilmurugan, Ramasamy,Ghosh, Kaushik
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p. 13829 - 13839
(2020/10/26)
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- Recyclable Pd/C catalyzed one-step reduction of carbonyls to hydrocarbons under simple conditions without extra base
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The reductions of carbonyls for the synthesis of hydrocarbons were developed with hydrazine hydrate, hydrogen gas and ammonium formate respectively. The simple, mild and efficient conditions were provided by employing recyclable Pd/C as catalyst in normal solvents at 100 °C and the reactions proceeded smoothly to produce the corresponding products with good to excellent yields. And gram-scale reactions and recycling of the catalyst were also demonstrated. Furtherly, the mechanism has been proposed.
- Zhou, Xiao-Yu,Chen, Xia
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supporting information
(2019/12/06)
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