- Sodium perborate: A convenient reagent for benzylic hydroperoxide rearrangement
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Sodium perborate in boron trifluoride etherate has been found to be an effective reagent for the hydroperoxide rearrangement of electron rich and highly substituted benzylic tertiary alcohols to phenols in good yields.
- Kabalka,Reddy,Narayana
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- Catalytic oxidation of aromatic hydrocarbons by a molecular iron-NHC complex
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An iron-NHC complex bearing a tetradentate bis(N-heterocyclic carbene) ligand is applied as catalyst for the oxidation of methyl substituted arene substrates. Using hydrogen peroxide as the oxidant p-xylene and pseudocumene are converted to the corresponding phenols and benzoquinones. The influence of various reaction parameters like temperature, catalyst loading, and oxidant concentration is investigated and kinetic experiments reveal that a temperature reduction leads to an increased catalyst lifetime. Furthermore, an interesting selectivity towards unexpected phenolic products resulting from a methyl shift reaction is observed.
- Lindhorst, Anja C.,Schütz, Jan,Netscher, Thomas,Bonrath, Werner,Kühn, Fritz E.
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- Photochemical reactions of oxygen atoms with toluene, m-xylene, p-xylene, and mesitylene: An infrared matrix isolation investigation
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The photochemical reactions of oxygen atoms with methylated benzenes (toluene, m-xylene, p-xylene, and mesitylene) were investigated in solid argon matrices at 12 K with UV light of λ ≥ 280 nm, producing ketene functionalities. The toluene/O atom reaction
- Parker, James K.,Davis, Steven R.
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- One-pot synthesis of phenols by hydroxylation of aromatics with hydroxylamine
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In this study, a new approach for one-pot synthesis of phenols is presented, i.e., benzene, ethylbenzene, and xylene were hydroxylated with hydroxylamine to give the corresponding phenols in good yield using molybdenum as a key catalyst.
- Zhang, Dongsheng,Gao, Liya,Xue, Wei,Zhao, Xinqiang,Wang, Shufang,Wang, Yanji
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- Application of two morphologies of Mn2O3for efficient catalyticortho-methylation of 4-chlorophenol
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Vapor phaseortho-methylation of 4-chlorophenol with methanol was studied over Mn2O3catalyst with two kinds of morphologies. Here, Mn2O3was prepared by a precipitation and hydrothermal method, and showed the morphology of nanoparticles and nanowires, respectively. XRD characterization and BET results showed that, with the increase of calcination temperature, Mn2O3had a higher crystallinity and a smaller specific surface area. N2adsorption/desorption and TPD measurements indicated that Mn2O3nanowires possessed larger external surface areas and more abundant acid and base sites. Simultaneously, in the fixed bed reactor, methanol was used as the methylation reagent for theortho-methylation reaction of 4-chlorophenol. XRD, XPS, TG-MS and other characterizations made it clear that methanol reduced 4-chlorophenol and its methide, which were the main side-reactions. And Mn3+was reduced to Mn2+under the reaction conditions. Changing the carrier gas N2to a H2/Ar mixture further verified that the hydrogen generated by the decomposition of methanol was not the reason for dechlorination of 4-chlorophenol compounds. Here we summarized the progress of 4-chlorophenol methylation based on the methylation of phenol. Also, we proposed a mechanism of the 4-chlorophenol dechlorination effect which was similar to the Meerwein-Ponndorf-Verley-type (MPV) reaction. The crystal phase and carbon deposition were investigated in different reaction periods by XRD and TG-DTA. The reaction conditions for the two kinds of morphologies of the Mn2O3catalyst such as calcination temperature, reaction temperature, phenol-methanol ratio and reaction space velocity were optimized.
- Gui, Wenying,Liu, Xiaofei,Wang, Zhenlu,Zhang, Chunlei,Zhang, Hongqiang,Zhang, Li,Zhu, Wanchun
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- The role of ion-molecule pair intermediates in acid-catalyzed solvolysis. General base-catalyzed formation of 4-methylbenzyl carbocation and its trapping by nucleophiles
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The specific acid-catalyzed hydrolysis of 3,6-dimethoxy-3,6-dimethyl-1,4- cyclohexadiene (1) in 25 vol % acetonitrile in water at 25 °C provides 2,4- dimethylphenol (2a), 2,5-dimethylphenol (2b), 2,4-dimethylanisole (3a), 4- methylbenzyl alcohol (4), and small amounts of 2,5-dimethylanisole (3b) and 4-methylbenzyl methyl ether (5). The formation of 3b and 5 is proposed to involve intramolecular rearrangement of carbocation-molecule pair intermediates. The formation of 4-methylbenzyl alcohol (4) is catalyzed by general bases, indicating that dehydronation of the cyclohexadienyl carbocation is rate-limiting in its reaction to benzylic products. The Bronsted parameter was measured with carboxylate anions as β = 0.28. The 4- methylbenzyl carbocation, which is postulated to be an intermediate in this reaction, discriminates between added nucleophiles and solvent water: k(SCN)/k(HOH) = 37, k(Cl)/K(HOH) = 9.8, k(EtOH)/k(HOH) = 1.9, and k(MeOH)/k(HOH) = 2.1 (ratios of second-order rate constants). The rate constant for reaction of the carbocation with solvent water is estimated as k(HOH) = 1.4 x 108 M-1s-1 (5.6 x 109 s-1), assuming a diffusion- controlled rate constant of 5 x 109 M-1s-1 for its reaction with thiocyanate anion. The nucleophilic selectivity values are considerably smaller than those exhibited by 4-methylbenzyl bromide under the same reaction conditions: k(Cl)/k(HOH) = 210, k(EtOH)/k(HOH) = 3.8, and k(MeOH)/k(HOH) = 5.3. These differences are concluded to be due to different mechanisms. The bromide reacts by a concerted bimolecular S(N)2 mechanism with chloride anion. With alcohols and water, the reactions occur either by a concerted uncoupled mechanism or via the ion pairs.
- Thibblin
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- Synthesis of substituted phenols via hydroxylation of arenes using hydrogen peroxide in the presence of hexaphenyloxodiphosphonium triflate
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A mild and efficient protocol for the synthesis of phenols from arenes has been developed using aqueous hydrogen peroxide as an oxidizing agent and hexaphenyloxodiphosphonium triflate as a promoter. The reactions were carried out with the simple procedure in EtOH-H2O at room temperature in short reaction times.
- Khodaei, Mohammad Mehdi,Alizadeh, Abdolhamid,Hezarkhani, Hadis Afshar
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- Evaluation of acute toxicity and genotoxicity of liquid products from pyrolysis of Eucalyptus grandis wood
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Slow pyrolysis of Eucalyptus grandis wood was performed in an oven laboratory, and smoke was trapped and condensed to yield liquid products. Polycyclic aromatic hydrocarbons (PAHs) and phenolic fractions were isolated from the former liquid products using adsorption column chromatography (ACC) and identified by GC/MS. Concentrations of PAH and phenolic fractions in total pyrolysis liquids were respectively 48.9 μg/g and 8.59% (w/w). Acute toxicity of total samples of pyrolysis liquids and the phenolic fraction was evaluated by means of two bioassays, namely, 24-h immobilization bioassay with Daphnia magna and Microtox(TM) bioassays, the latter employing the luminescent bacteria Photobacterium phosphoreum. Total pyrolysis liquids and the PAH fraction were evaluated for genotoxicity by the Microtox(TM) bioassay conducted using rehydrated freeze-dried dark mutant of the luminescent bacteria Vibrio fisheri strain M169. Total pyrolysis liquids and the phenolic fraction, respectively, in concentrations of 170 and 68 mg/L were able to immobilize 50% (EC50) of the D. magna population following 24-h exposure. Concentrations of 19 and 6 mg/L, respectively, for total pyrolysis liquids and phenolic fraction were the effective concentrations that resulted in a 50% (EC50) reduction in light produced by bacteria in the Microtox(TM) bioassay. Accordingly, the Microtox(TM) bioassay was more sensitive to toxic effects of both kind of samples than the D. magna bioassay, particularly for the phenolic fraction. Regarding to the genotoxicity evaluation, the results achieved by Microtox(TM) bioassay showed that total pyrolysis liquids had no genotoxic effects with and without exogenous metabolic activation using rat liver homogenate (S9). However, the PAH fraction showed toxic effects with rat liver activation and had a dose-response number (DRN) equal to 1.6, being in this way suspected genotoxic. The lowest detected concentration (LDC) of the PAH fraction able to cause genotoxic effects was 375 μg/L.
- Pimenta,Bayona,Garcia,Solanas
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- Photoinduced Decomposition of Peracetic Acid in Xylenes. Orientation in Aromatic Substitution of Methyl and Hydroxyl Radicals
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The photolysis of peracetic acid (1) in o-,m- or p-xylenes (2) has been carried out using 2537-Angstroem or >2900-Angstroem light at 20-22 deg C.The yields of ethyltoluenes (3), trimethylbenzenes (4), and dimethylphenols (6) are higher at 2537-Angstroem than those at >2900-Angstroem photolysis, but the reverse is true with the yield of methylbenzyl alcohol (5).The isomer distribution of trimethylbenzenes (4) formed from o- (2a) or m-xylene (2b) suggests that an attack of methyl radical at the position meta to the methyl group is favored with 2537-Angstroem light, while an attack at the ortho position is preferential with >2900-Angstroem light.On the other hand, the isomer distribution of dimethylphenols (6) at 2537 Angstroem suggests that an attack of hydroxyl radical is favored at positions ortho and para to the methyl group.These orientations of radical attack are briefly discussed.
- Ogata, Yoshiro,Tomizawa, Kohtaro
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- Highly Selective and Efficient Ring Hydroxylation of Alkylbenzenes with Hydrogen Peroxide and an Osmium(VI) Nitrido Catalyst
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The OsVI nitrido complex, OsVI(N)(quin)2(OTs) (1, quin=2-quinaldinate, OTs=tosylate), is a highly selective and efficient catalyst for the ring hydroxylation of alkylbenzenes with H2O2 at room temperature. Oxidation of various alkylbenzenes occurs with ring/chain oxidation ratios ranging from 96.7/3.3 to 99.9/0.1, and total product yields from 93 % to 98 %. Moreover, turnover numbers up to 6360, 5670, and 3880 can be achieved for the oxidation of p-xylene, ethylbenzene, and mesitylene, respectively. Density functional theory calculations suggest that the active intermediate is an OsVIII nitrido oxo species.
- Kwong, Hoi-Ki,Lo, Po-Kam,Yiu, Shek-Man,Hirao, Hajime,Lau, Kai-Chung,Lau, Tai-Chu
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- Effect of Co incorporation and support selection on deoxygenation selectivity and stability of (Co)Mo catalysts in anisole HDO
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A series of supported Co modified Mo catalysts was prepared by varying the Co/Mo ratio in the range from 0 to 1 while maintaining the Mo loading at ca. 10 wt%. A sequential incipient wetness impregnation method, with Mo being introduced first, using aqueous solutions of the corresponding precursor salts was employed during the synthesis procedure. Three supports, i.e., Al2O3, ZrO2, and TiO2 differing in textural and acidic properties were investigated. Material physicochemical characteristics were evaluated through ICP-OES, N2-sorption, XRD, H2-TPR, NH3-TPD, O2-TPO, STEM-EDX and XPS techniques. The anisole HDO performance of these CoMo catalysts was evaluated at gas phase conditions in a fixed bed tubular reactor in plug flow regime. The catalysts performance is correlated with properties such as reducibility, acidity, and metal-support interactions. Cobalt addition enhanced the total HDO selectivity by 45% as compared to Mo catalysts. Alumina catalysts displayed higher initial activity (Xanisole≈97%) relative to titania and zirconia supported variants (Xanisole 5+ to be the main active phase while over-reduction to lower Mo states (Mo4+ and Mo3+) as well as carbon deposition are identified as the cause for catalyst activity decrease with TOS.
- Ranga, Chanakya,Alexiadis, Vaios I.,Lauwaert, Jeroen,L?deng, Rune,Thybaut, Joris W.
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- Efficient Transformation of Anisole into Methylated Phenols over High-Silica HY Zeolites under Mild Conditions
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Transformation of anisole (methoxybenzene), a typical component of bio-oil, into phenol and methylated phenols was studied over HY zeolites with framework Si/Al ratios of 5, 15, 25, and 35. It was demonstrated that the amounts of Bronsted acid and Lewis acid sites, the ratio of Lewis acid and Bronsted acid sites, and the textural properties of the zeolites were all crucial parameters that influenced the catalytic performance. The Bronsted acid and Lewis acid sites of the zeolites catalyzed the reaction cooperatively and efficiently promoted the transmethylation. The hierarchical channel system with fully open micropore-mesopore connectivity was favorable to reduce the amount of coke generated.
- Meng, Qinglei,Fan, Honglei,Liu, Huizhen,Zhou, Huacong,He, Zhenhong,Jiang, Zhiwei,Wu, Tianbin,Han, Buxing
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- Synthesis of mono- and polycyclic tricarbonyliron cyclohexa-2,4-dienone complexes and phenols from tosylhydrazones of acyclic dienone complexes
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Cyclohexa-2,4-dienones stabilized by coordination to tricarbonyliron are obtained when the tosylhydrazones of tricarbonyliron-complexed α-dienones are thermolyzed in the presence of strong bases. This cyclocarbonylation reaction of carbenic intermediates is fairly general and can be used to synthesize various mono and polycyclic cyclohexadienone complexes or their decomplexed phenolic tautomers, and among them a new salicylate in the phenanthrene series.
- Franck-Neumann, Michel,Geoffroy, Philippe,Gassmann, Dominique
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- A new mild deprotecting method for O-benzylsulfonyl phenols and alcohols based on a DTBB-catalyzed lithiation
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A variety of alcohols and phenols, protected as the corresponding benzylsulfonic esters, were efficiently deprotected by selective reductive cleavage of the sulfur-oxygen bond, using an excess of lithium sand and a catalytic amount (5 mol%) of 4,4′-di-tert-butylbiphenyl (DTBB) as electron carrier, in THF at 0° C. This deprotection system was also efficient at -50 °C and was compatible with a wide range of other functional groups. Georg Thieme Verlag Stuttgart.
- Alonso, Francisco,Moglie, Yanina,Vitale, Cristian,Radivoy, Gabriel,Yus, Miguel
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- Carbonyl Oxide Chemistry. The NIH Shift
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Benzophenone oxide has been shown to oxidize 1-chloronaphthalene and p-xylene with accompanying NIH shift of chlorine and methyl, respectively.Similar oxidation of toluene leads to a mixture of o-,p-, and m-cresols while N-acetyl-L-phenylalanine ethyl ester is oxidized to the corresponding tyrosine derivative.The results are discussed in terms of their relationship to the "activation" of polycyclic aromatic hydrocarbons in polluted atmospheres and the possible production of mutagens/carcinogens.
- Kumar, S.,Murray, R. W.
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- ipso-Attack in the Hydroxylation of o- and p-Xylene using bis(trimethylsilyl) Peroxide and Aluminium Chloride
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Electrophilic hydroxylation of o- and p-xylene using a range of peroxides, including the title compound, in the presence of Lewis acids results in the formation of mixtures of phenols including those derived by ipso-attack followed by rearrangement; ipso-attack by the hydroxyl radical leads to dealkylation.
- Apatu, Jonas O.,Chapman, David C.,Heaney, Harry
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- Improved oxidation of aromatic and aliphatic hydrocarbons using rate enhancing variants of P450Bm3 in combination with decoy molecules
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Enzyme performance can be improved using decoy molecules or engineered variants to accelerate the activity without affecting selectivity. Here we combine a rate accelerator variant of cytochrome P450Bm3 with decoy molecules to enhance the oxidation activity of a range of small organic molecules. This combined approach offers superior biocatalytic efficiency without modifying the product distribution.
- Munday, Samuel D.,Shoji, Osami,Watanabe, Yoshihito,Wong, Luet-Lok,Bell, Stephen G.
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- Comparison of cresol transformation on USHY and HZSM-5
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In the commercial synthesis of cresols, the most common processes include the alkylation of phenol with methanol. The cresol (methylphenol) transformation on zeolite USHY was studied and compared with HZSM-5 with different pore size, structure, and different acidity in a flow reactor at 380°C and 0.1 bar. The cresol turnover numbers for USHY were pretty similar, whereas on HZSM-5, the cresols reactivities followed the sequence p- ≥ m- > o-cresol. The cresols reacted over the zeolites mainly through two parallel reactions, isomerization and disproportionation, whose relative importance depends on the catalysts characteristics (pore structure and acidity), on the reacting cresol itself, and on the reaction conditions (temperature, total pressure, reactant partial pressure, etc). The USHY selectivity toward the monomolecular isomerization reaction was by far lower than that of HZSM-5, due to its size/shape selectivity. On USHY and HZSM-5 catalysts, the o-cresol showed higher disproportionation selectivity than the other two cresol isomers, this proportionation occurring via diphenylmethane intermediates. The cresol isomerization selectivity was limited by product desorption even on a large pore zeolite like USHY. The cresol isomer composition at high conversions on USHY was 44, 42, and 14% for o-, m-, and p-cresol, respectively. Xylenols underwent a rapid isomerization once formed.
- Imbert,Guisnet,Gnep
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- PHOTOCHEMICAL ELECTRON TRANSFER REACTIONS OF 4-TRICHLOROMETHYL-4-METHYL-2,5-CYCLOHEXADIEN-1-ONES
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Ultraviolet irradiation of the title compounds in amine solvents results in transformations attributed to initial formation of radical ions by electron transfer, the quantum efficiency of reaction depending on the ionization potential of the amine.
- Schuster, David I.,Brisimitzakis, Angelo C.
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- Ortho-alkylation of phenol with methanol using Pb-Cr promoted magnesium oxide catalysts
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In this study, Pb-Cr promoted magnesium oxide catalysts were used to catalyze the ortho-alkylation of phenol in the presence of excess methanol. The Cr/MgO catalyst exhibited a high conversion of phenol and a relatively high selectivity for the ortho-alkylation of phenol. The catalytic activity and the stability of Cr/MgO were improved by the addition of a fairly small amount of Pb. The Pb-Cr/MgO catalyst showed specificity for the ortho-alkylation of phenol, which was proved by a series of phenol derivative reactions with methanol.
- Ke, Jyh-Harng,Zena, Jyh-Myng,Wang, Fey-Long
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- Palladium-catalyzed hydroxylation of aryl and heteroaryl halides enabled by the use of a palladacycle precatalyst
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A method for the hydroxylation of aryl and heteroaryl halides, promoted by a catalyst based on a biarylphosphine ligand tBuBrettPhos (L5) and its corresponding palladium precatalyst (1), is described. The reactions allow the cross-coupling of both potassium and cesium hydroxides with (hetero)aryl halides to afford a variety of phenols and hydroxylated heteroarenes in high to excellent yield.
- Cheung, Chi Wai,Buchwald, Stephen L.
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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; 12
(2021/08/14)
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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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- 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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- 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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- Reductive Aromatization of Quinols with B2pin2 as Deoxidizing Agent
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We have demonstrated B2pin2 as superior deoxidizing agent for the reductive deoxygenation of quinol derivatives under basic conditions. A wide range of highly functionalized phenols were obtained in good yields including a complex drug molecule, which revealed the high functional group tolerance of this protocol.
- Liu, Bin,Xu, Yin,Luo, Zhibin,Xie, Jimin
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supporting information
p. 1022 - 1024
(2020/03/19)
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- Substrate substitution effects in the Fries rearrangement of aryl esters over zeolite catalysts
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The catalytic transformation of aryl esters to hydroxyacetophenones via Fries rearrangement over solid acids is of interest to avoid the use of corrosive and toxic Lewis and Br?nsted acids traditionally applied. Microporous zeolites are known to catalyze the reaction of simple substrates such as phenyl acetate, but their application to substituted derivatives has received limited attention. To refine structure-activity relationships, here we examine the impact of various parameters including the solvent polarity, water content, acidic properties, and framework type on the reaction scheme in the Fries rearrangement of p-tolyl acetate over common solid acids. The results confirm the importance of providing a high concentration of accessible Br?nsted acid sites, with beta zeolites exhibiting the best performance. Extension of the substrate scope by substituting methyl groups in multiple positions identifies a framework-dependent effect on the rearrangement chemistry and highlights the potential for the transformation of dimethylphenyl acetates. Kinetic studies show that the major competitive path of cleavage of the ester C-O bond usually occurs in parallel to the Fries rearrangement. The possibility of sequentially acylating the resulting phenol depends on the substrate and reaction conditions.
- Bonrath, Werner,Létinois, Ulla,Lin, Ronghe,Medlock, Jonathan,Mitchell, Sharon,Netscher, Thomas,Pérez-Ramírez, Javier,Stemmler, René T.
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p. 4282 - 4292
(2020/07/30)
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- Nanoporous Na+-montmorillonite perchloric acid as an efficient and recyclable catalyst for the chemoselective protection of hydroxyl groups
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Nanoporous Na+-montmorillonite perchloric acid as a novel heterogeneous reusable solid acid catalyst was easily prepared by treatment of Na+-montmorillonite as a cheap and commercially available support with perchloric acid. The catalyst was characterized using a variety of techniques including X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), energy dispersive X-ray spectroscopy (EDX), pH analysis and determination of the Hammett acidity function. The prepared reagent showed excellent catalytic activity for the chemoselective conversion of alcohols and phenols to their corresponding trimethylsilyl ethers with 1,1,1,3,3,3-hexamethyldisilazane (HMDS) at room temperature. Deprotection of the resulting trimethylsilyl ethers can also be carried out using the same catalyst in ethanol. All reactions were performed under mild and completely heterogeneous reaction conditions in good to excellent yields. The notable advantages of this protocol are: short reaction times, high yields, availability and low cost of the reagent, easy work-up procedure and the reusability of the catalyst during a simple filtration.
- Mashhadinezhad, Maryam,Shirini, Farhad,Mamaghani, Manouchehr
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p. 2099 - 2107
(2019/01/03)
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- Regioselectivity of Hydroxyl Radical Reactions with Arenes in Nonaqueous Solutions
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The regioselectivity of hydroxyl radical addition to arenes was studied using a novel analytical method capable of trapping radicals formed after the first elementary step of reaction, without alteration of the product distributions by secondary oxidation processes. Product analyses of these reactions indicate a preference for o- over p-substitution for electron donating groups, with both favored over m-addition. The observed distributions are qualitatively similar to those observed for the addition of other carbon-centered radicals, although the magnitude of the regioselectivity observed is greater for hydroxyl. The data, reproduced by high accuracy CBS-QB3 computational methods, indicate that both polar and radical stabilization effects play a role in the observed regioselectivities. The application and potential limitations of the analytical method used are discussed.
- Moores, Lee C.,Kaur, Devinder,Smith, Mathew D.,Poole, James S.
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p. 3260 - 3269
(2019/03/11)
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- Catalytic activation of unstrained C(aryl)–C(aryl) bonds in 2,2′-biphenols
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Transition metal catalysis has emerged as an important means for C–C activation that allows mild and selective transformations. However, the current scope of C–C bonds that can be activated is primarily restricted to either highly strained systems or more polarized C–C bonds. In contrast, the catalytic activation of non-polar and unstrained C–C moieties remains an unmet challenge. Here we report a general approach for the catalytic activation of the unstrained C(aryl)–C(aryl) bonds in 2,2′-biphenols. The key is to utilize the phenol moiety as a handle to install phosphinites as a recyclable directing group. Using hydrogen gas as the reductant, monophenols are obtained with a low catalyst loading and high functional group tolerance. This approach is also applied to the synthesis of 2,3,4-trisubstituted phenols. A further mechanistic study suggests that the C–C activation step is mediated by a rhodium(i) monohydride species. Finally, a preliminary study on breaking the inert biphenolic moieties in lignin models is illustrated.
- Zhu, Jun,Wang, Jianchun,Dong, Guangbin
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- Identification of an Oxalamide Ligand for Copper-Catalyzed C?O Couplings from a Pharmaceutical Compound Library
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A typical pharmaceutical compound library is stocked with molecular diversity and could provide a platform for the discovery of new ligand structures. Herein, we describe the use of this approach in combination with high throughput screening to identify N,N’-bis(thiophene-2-ylmethyl)oxalamide as a ligand that is generally effective for copper-catalyzed C?O cross-couplings to prepare both biarylethers as well as phenols under mild conditions.
- Chan, Vincent S.,Krabbe, Scott W.,Li, Changfeng,Sun, Lijie,Liu, Yue,Nett, Alex J.
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- SYSTEMS AND METHODS FOR SYNTHESIS OF PHENOLICS AND KETONES
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Embodiments herein relate to apparatus and systems for phenolic and ketone synthesis and methods regarding the same. In an embodiment, a method of producing phenolics and ketones is included. The method can specifically include forming a reaction mixture comprising nanocrystalline cellulose (NCC) and water. The method can also include contacting the reaction mixture with a metal oxide catalyst at a temperature of 350 degrees Celsius or higher and a pressure of at least about 3200 psi to form a reaction product mixture. The reaction product mixture can include at least about 20 wt. % phenolics and at least about 10 wt. % ketones as a percentage of the total mass of nanocrystalline cellulose (NCC). Other embodiments are also included herein.
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Paragraph 0080-0088
(2018/11/21)
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- Tuning the Reactivity of Peroxo Anhydrides for Aromatic C-H Bond Oxidation
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Phenol moieties are key structural motifs in many areas of chemical research from polymers to pharmaceuticals. Herein, we report on the design and use of a structurally demanding cyclic peroxide (spiro[bicyclo[2.2.1]heptane-2,4′-[1,2]dioxolane]-3′,5′-dione, P4) for the direct hydroxylation of aromatic substrates. The new peroxide benefits from high thermal stability and can be synthesized from readily available starting materials. The aromatic C-H oxidation using P4 exhibits generally good yields (up to 96%) and appreciable regioselectivities.
- Pilevar, Afsaneh,Hosseini, Abolfazl,?ekutor, Marina,Hausmann, Heike,Becker, Jonathan,Turke, Kevin,Schreiner, Peter R.
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p. 10070 - 10079
(2018/09/06)
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- Hydrogenation of lignin-derived phenolic compounds over step by step precipitated Ni/SiO2
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The harsh reaction conditions for the valorization of lignin-derived phenolic compounds considerably limit the efficient utilization of the lignin derivatives. Here, we put forward a high efficient and selective hydrogenation process for phenolic compounds at a mild condition over step by step precipitated Ni/SiO2 catalyst. The properties of the Ni/SiO2 catalysts by different preparation methods were detailedly compared using various characterization measurements. Catalytic activity of the catalysts was tested by the hydrogenation of guaiacol, and the results showed that guaiacol could be completely converted into cyclohexanol with 99.9% selectivity at 120 °C, 2 MPa H2 atmosphere for 2 h. Other typical lignin-derived phenolic compounds also had excellent hydrogenation performance and great energy efficiency. Catalyst characterization results demonstrated that the high catalytic activity of the step by step precipitated Ni/SiO2 was mainly ascribed to its polyporous spherical structure, which led to the large specific surface area and high nickel dispersion. The appropriate acidity of the catalyst also promoted the catalytic performance significantly. Furthermore, the catalyst exhibited an excellent recyclability, where no significant loss of the catalytic activity was showed out after 3 runs.
- Shu, Riyang,Zhang, Qi,Xu, Ying,Long, Jinxing,Ma, Longlong,Wang, Tiejun,Chen, Pengru,Wu, Qingyun
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p. 5214 - 5222
(2016/02/05)
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- One-Pot Defunctionalization of Lignin-Derived Compounds by Dual-Functional Pd50Ag50/Fe3O4/N-rGO Catalyst
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Generation of hydrogen from renewable sources and its safe utilization for efficient one-pot upgrading of renewable biofuels are a challenge. Bimetallic PdAg catalyst supported on Fe3O4/nitrogen-doped reduced graphene oxide (N-rGO) were synthesized for hydrogen generation from formic acid with high TOF (497 h-1 at 50 °C), and the hydrogen was subsequently utilized in situ for selective defunctionalization of lignin-derived chemicals with preserved aromatic nature at ambient pressure. Hydrodeoxygenation of aromatic aldehydes and ketones gave excellent yields (99% at 130 °C) with no use of additives. Furthermore, hydrogenolysis of β-O-4 and α-O-4 C-O model compounds produced only two products with high selectivity at 120 °C, which is an efficient and versatile one-pot platform for valorization of lignin biomass.
- Singh, Ajay K.,Jang, Seungwook,Kim, Jae Yul,Sharma, Siddharth,Basavaraju,Kim, Min-Gyu,Kim, Kyung-Rok,Lee, Jae Sung,Lee, Hong H.,Kim, Dong-Pyo
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p. 6964 - 6972
(2015/11/18)
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- Phenol methylation on acid catalysts: Study of the catalyst deactivation kinetics and mechanism
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The kinetics and mechanism of coke formation and catalyst deactivation during the synthesis of cresols from phenol methylation were investigated on SiO2-Al2O3, tungstophosphoric acid (HPA) supported on silica, and zeolites HBEA, HZSM5, HMCM22 and HY. The nature, density and strength of surface acid sites were probed by temperature programmed desorption of NH3 coupled with infrared spectra of adsorbed pyridine. Coke formed on the catalysts during reaction was characterized by temperature programmed oxidation. All the samples deactivated on stream. A linear correlation was observed between the initial catalyst deactivation and the amount of coke, thereby indicating that coke formation was responsible for the activity decay. Coking kinetic studies showed that a significant part of coke was rapidly formed from the reactants. When methanol was feeding alone, significant amounts of carbon were formed on the catalysts (between 0.6% and 6.2%C), particularly on samples containing mainly strong Br?nsted acid sites. Nevertheless, the coke amounts formed during phenol methylation were clearly higher (between 3.7% and 14.9%C), which showed that phenol was also responsible for coke formation. More insight on the role of phenol and methanol on coke formation was obtained by characterizing the coke nature using infrared spectroscopy. Coked samples recovered after methanol decomposition reaction exhibited IR absorption bands characteristics of olefinic species formed on Br?nsted and Lewis acid sites. The IR spectra of coked samples recovered after phenol methylation showed the presence of phenolate, aromatic and polyaromatic species adsorbed mainly on Lewis acid sites.
- Sad,Padró,Apesteguía
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p. 305 - 313
(2014/03/21)
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- Synthesis of deuterated benzopyran derivatives as selective COX-2 inhibitors with improved pharmacokinetic properties
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We designed a series of specifically deuterated benzopyran analogues as new COX-2 inhibitors with the aim of improving their pharmacokinetic properties. As expected, the deuterated compounds retained potency and selectivity for COX-2. The new molecules possess improved pharmacokinetic profiles in rats compared to their nondeuterated congeners. Most importantly, the new compounds showed pharmacodynamic efficacy in several murine models of inflammation and pain. The benzopyran derivatives were separated into their enantiomers, and the activity was found to reside with the S-isomers. To streamline the synthesis of the desired S-isomers, an organocatalytic asymmetric domino oxa-Michael/aldol condensation reaction was developed for their preparation.
- Zhang, Yanmei,Tortorella, Micky D.,Wang, Yican,Liu, Jianqi,Tu, Zhengchao,Liu, Xiaorong,Bai, Yang,Wen, Dingsheng,Lu, Xin,Lu, Yongzhi,Talley, John J.
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p. 1162 - 1166
(2014/12/10)
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- CYCLIC PEROXIDE OXIDATION OF AROMATIC COMPOUND PRODUCTION AND USE THEREOF
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The present invention provides a method for converting an aromatic hydrocarbon to a phenol by providing an aromatic hydrocarbon comprising one or more aromatic C-H bonds and one or more activated C-H bonds in a solvent; adding a phthaloyl peroxide to the solvent; converting the phthaloyl peroxide to a di-radical; contacting the di-radical with the one or more aromatic C-H bonds; oxidizing selectively one of the one or more aromatic C-H bonds in preference to the one or more activated C-H bonds; adding a hydroxyl group to the one of the one or more aromatic C-H bonds to form one or more phenols; and purifying the one or more phenols.
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Page/Page column 9; 10
(2014/10/15)
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- One step C-N bond formation from alkylbenzene and ammonia over Cu-modified TS-1 zeolite catalyst
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A Cu doped TS-1 zeolite sample was applied to catalyze the formation of C-N bonds on both the ring and the side chain of toluene, as well as other alkylbenzenes. A yield of 3.4% of toluidine was obtained for the amination of toluene, with a 1.0% yield of nitrobenzene. Cyanobenzene was also obtained as the C-N bond product on the side chain with a yield of 1.0%. The selectivity for C-N bond formation was 52.4%. The catalyst promoted the formation of a hydroxylamine intermediate from ammonia and hydrogen peroxide, and then the instantaneously generated amino cation reacted with the substrate to form C-N bonds on both the ring and side chain. Cyanobenzene was produced from the dehydration of benzylamine, formed via the reaction of ammonia and toluene. The formation of C-N bonds on the ring had an ortho-orientation advantage for mono-substituted-benzenes. With the increase in the number of methyl substituents, the yield of the ring products decreased, which might be caused by steric hindrance. the Partner Organisations 2014.
- Xia, Sheng,Yu, Tianhua,Liu, Huihui,Li, Guiying,Hu, Changwei
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p. 3108 - 3119
(2014/08/18)
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- Metal-free oxidation of aromatic carbon-hydrogen bonds through a reverse-rebound mechanism
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Methods for carbon-hydrogen (C-H) bond oxidation have a fundamental role in synthetic organic chemistry, providing functionality that is required in the final target molecule or facilitating subsequent chemical transformations. Several approaches to oxidizing aliphatic C-H bonds have been described, drastically simplifying the synthesis of complex molecules. However, the selective oxidation of aromatic C-H bonds under mild conditions, especially in the context of substituted arenes with diverse functional groups, remains a challenge. The direct hydroxylation of arenes was initially achieved through the use of strong Bronsted or Lewis acids to mediate electrophilic aromatic substitution reactions with super-stoichiometric equivalents of oxidants, significantly limiting the scope of the reaction. Because the products of these reactions are more reactive than the starting materials, over-oxidation is frequently a competitive process. Transition-metal-catalysed C-H oxidation of arenes with or without directing groups has been developed, improving on the acid-mediated process; however, precious metals are required. Here we demonstrate that phthaloyl peroxide functions as a selective oxidant for the transformation of arenes to phenols under mild conditions. Although the reaction proceeds through a radical mechanism, aromatic C-H bonds are selectively oxidized in preference to activated-H bonds. Notably, a wide array of functional groups are compatible with this reaction, and this method is therefore well suited for late-stage transformations of advanced synthetic intermediates. Quantum mechanical calculations indicate that this transformation proceeds through a novel addition-abstraction mechanism, a kind of 'reverse-rebound' mechanism as distinct from the common oxygen-rebound mechanism observed for metal-oxo oxidants. These calculations also identify the origins of the experimentally observed aryl selectivity.
- Yuan, Changxia,Liang, Yong,Hernandez, Taylor,Berriochoa, Adrian,Houk, Kendall N.,Siegel, Dionicio
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p. 192 - 196
(2013/08/23)
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- Preparation, characterization and use of 1,3-disulfonic acid imidazolium hydrogen sulfate as an efficient, halogen-free and reusable ionic liquid catalyst for the trimethylsilyl protection of hydroxyl groups and deprotection of the obtained trimethylsilanes
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Novel 1,3-disulfonic acid imidazolium hydrogen sulfate, a halogen-free ionic liquid, is a recyclable and eco-benign catalyst for the trimethylsilyl protection of hydroxyl groups at room temperature under solvent free conditions to afford trimethylsilanes in excellent yields (92-100%) and in very short reaction times (1-5 min). Deprotection of the resulting trimethylsilanes can also be achieved using the same catalyst in methanol. The catalyst was characterized by IR, 1H NMR, 13C NMR and MS studies. All the products were extensively characterized by IR, 1H NMR, MS, and elemental and melting point analyses. This new method consistently has the advantages of excellent yields and short reaction times. Further, the catalyst can be recovered and reused for several times without loss of activity. The work-up of the reaction consists of a simple separation, followed by concentration of the crude product and purification.
- Shirini, Farhad,Khaligh, Nader Ghaffari,Akbari-Dadamahaleh, Somayeh
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- Nanocrystalline TiO2-HClO4 as a new, efficient and recyclable catalyst for the chemoselective trimethylsilylation of alcohols, phenols and deprotection of silyl ethers
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TiO2-HClO4, as a new solid acid, was found to be an efficient catalyst for the chemoselective trimethylsilylation of alcohols and phenols. Deprotection of the resulting trimethylsilylethers was achieved using the same catalyst in methanol solvent. The synthesized catalyst was characterized by FT-IR, SEM, TEM, BET and XRD analyses. Our novel synthetic method has the advantages of high yields, short reaction times, low cost and recyclability of the catalyst, simplicity and easy work-up compared to the conventional methods reported in the literature.
- Shirini, Farhad,Atghia, Seyyed Vahid,Jirdehi, Mojtaba Ghazi
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- Square-planar mesitylenido(triphenylphosphane)nickel(II) complexes containing bidendate N,O-ligands: Changes in catalytic efficiency upon small alterations in the ligand backbone
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Square planar arenido(triphenylphosphane)nickel(II) complexes containing a heterocyclic bidentate N,O-chelate ligand are catalysts for the copolymerisation of ethene and carbon monoxide. To examine the influence of the N,O-ligand on the catalytic activity new nickel(II) complexes with altered heterocyclic ring size in the corresponding N,O-ligands were synthesised and fully characterised. The crystal structures of all protonated N,O-ligands and the corresponding nickel complexes were determined. The catalytic activity of the new complexes in the copolymerisation reaction of ethene and carbon monoxide as well as in the polymerisation reaction of ethene were studied.
- Beckmann, Udo,Lindner, Monika M.,Eichberger, Eva,Frank, Walter
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p. 73 - 80,8
(2020/08/24)
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- Chemo- and regioselective direct hydroxylation of arenes with hydrogen peroxide catalyzed by a divanadium-substituted phosphotungstate
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Peroxide in, phenol out: The catalyst [-PW10O38V 2(μ-OH)2]3- showed high activity in the hydroxylation of various aromatic compounds with aqueous H2O 2. The system was regioselective, producing para-phenols from monosubstituted benzene derivatives. Furthermore, alkylarenes with reactive side-chain Ca spa 3-H bonds could be chemoselectively hydroxylated without significant formation of side-chain oxygenated products. Copyright
- Kamata, Keigo,Yamaura, Taiyo,Mizuno, Noritaka
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supporting information; experimental part
p. 7275 - 7278
(2012/08/28)
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- CuI-catalyzed hydroxylation of aryl bromides under the assistance of 5-bromo-2-(1H-imidazol-2-yl)pyridine and related ligands
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A number of substituted 2-pyridin-2-yl-1H-benzoimidazoles and 2-(1H-imidazol-2-yl)pyridines were screened for promoting CuI-catalyzed hydroxylation of aryl bromides, which led to the discovery of the combination of CuI and 5-bromo-2-(1H-imidazol-2-yl)pyridine as an effective catalytic system for this transformation. Both electron-rich and electronic-deficient aryl bromides could be converted into the corresponding substituted phenols in good to excellent yields.
- Jia, Jianhuan,Jiang, Chenglin,Zhang, Xiaojing,Jiang, Yongwen,Ma, Dawei
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supporting information; experimental part
p. 5593 - 5595
(2011/11/06)
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- Copper-catalyzed hydroxylation of aryl halides with tetrabutylammonium hydroxide: Synthesis of substituted phenols and alkyl aryl ethers
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The selective hydroxylation of aryl iodides and aryl bromides with tetrabutylammonium hydroxide pentahydrate is described. For this, the combination of copper(I) iodide and 8-hydroxyquinaldine at 70-130C in a mixture of dimethyl sulfoxide and water (2:3) is used. The resultant phenols can be readily reacted with alkyl and allyl halides in situ to provide the corresponding alkyl or allyl aryl ethers in high yields. The reactions are simple, general, and efficient, affording substituted phenols and alkyl aryl ethers under aerobic conditions
- Paul, Rajesh,Ali, Md Ashif,Punniyamurthy, Tharmalingam
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supporting information; experimental part
p. 4268 - 4272
(2011/02/25)
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- Role of transalkylation reactions in the conversion of anisole over HZSM-5
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Conversion of anisole, a typical component of bio-oil, was studied over an HZSM-5 zeolite at varying space times (W/F), reaction temperatures, type of carrier gas, and concentration of water in the feed. Several bimolecular and unimolecular reactions are proposed to explain the evolution of products observed. The bimolecular reactions include the following transalkylation reactions: (a) anisoles to phenol and methylanisole; (b) phenol and methylanisole to cresols; (c) phenol and anisole to cresol and phenol; (d) methylanisole and cresol to phenol and xylenol. A pseudo first-order kinetic model based on these bimolecular reactions was found to describe well the observed product distribution as a function of W/F. It is observed that shape selectivity effects prevail over electrophilic substitution and thermodynamic equilibrium effects in the formation of methylanisole isomers. However, the opposite is true for the distribution of cresol isomers. The kinetic analysis indicates that the contribution of unimolecular reactions such as isomerization is much lower than that of bimolecular reactions. The carrier gas composition was found to have a moderate effect on catalyst activity. When H2 was used as a carrier, catalyst stability showed a moderate improvement in comparison to the runs under He. However, a remarkable increase in catalytic activity was observed upon the addition of water in the feed.
- Zhu, Xinli,Mallinson, Richard G.,Resasco, Daniel E.
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experimental part
p. 172 - 181
(2010/09/05)
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- Gold-catalyzed rearrangement of substituted allyl aryl ethers
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Triphenylphosphinegold(I) complexes catalyze the Claisen-type rearrangement of aryl allyl ethers to the corresponding branched and linear products. The product distribution depends on the olefin geometry of the allylic ether. Stereochemical transfer experiments support an ionic mechanism.
- Vyvyan, James R.,Dimmitt, Heidi E.,Griffith, Jennifer K.,Steffens, Laura D.,Swanson, Rebecca A.
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experimental part
p. 6666 - 6669
(2011/02/21)
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- Convergent synthesis of geometrically disassembling dendrimers using Cu(I)-catalyzed C-O bond formation
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The convergent synthesis of geometrically degradable dendrimers based on the 2,4-bis(hydroxymethyl)phenol subunit is presented. The key step of the synthetic scheme involves the CuI/3,4,7,8-tetramethyl-1,10-phenanthroline- catalyzed coupling of aryl iodides and alcohols. The synthesis and disassembly of these compounds is discussed.
- Polaske, Nathan W.,Szalai, Michael L.,Shanahan, Charles S.,McGrath, Dominic V.
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supporting information; experimental part
p. 4944 - 4947
(2010/12/25)
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- Study of the phenol methylation mechanism on zeolites HBEA, HZSM5 and HMCM22
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The mechanism of gas-phase alkylation of phenol with methanol was studied on zeolites HBEA, HZSM5 and HMCM22. The nature, density and strength of the acid sites were determined by temperature-programmed desorption of NH3 and FTIR spectroscopy of adsorbed pyridine. In all the cases, anisole, o-cresol and p-cresol were the primary products, but the initial product distribution greatly depended on the zeolite pore structure and surface acid properties. The complete reaction network was established by investigating the formation of secondary products (xylenols, methylanisoles, m-cresol) via the reactions of primary products with phenol and methanol. On HBEA, phenol was alkylated to primary and secondary products without significant diffusional restraints and the yield to dialkylated products increased when phenol conversion was increased. o-Cresol was consecutively alkylated to 2,4- and 2,6-xylenols (C-alkylation), and 2-methylanisole (O-alkylation). Anisole reacted with phenol to yield o- and p-cresol isomers, and with methanol to form methylanisoles. Selectivities to primary products on HZSM5 were similar to those determined on HBEA, but the formation of bulky intermediates leading to dialkylated compounds was hampered because of diffusional constraints. The alkylation of phenol with anisole to yield cresol isomers was completely suppressed on HZSM5. The particular pore structure of zeolite HMCM22 promoted the selective formation of p-cresol among the primary products of phenol methylation and drastically suppressed the consecutive reactions forming secondary products. In contrast, isomerization reactions between monoalkylated products were promoted on zeolite HMCM22 because of its high concentration of strong Br?nsted acid sites. The activity decay on stream was significant on the three zeolites, probably because of the formation of coke intermediates via both anisole dealkylation and methanol dehydration reactions.
- Sad,Padró,Apesteguía
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scheme or table
p. 63 - 72
(2010/11/18)
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- Reaction of atomic carbon with isomeric cresols
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Reaction of atomic carbon with isomeric cresols generates methyltropones and xylenols. Methyltropone to xylenol ratio was found to be highest for m-cresol and lowest for p-cresol. Stability of singlet carbenes produced after insertion of atomic carbon int
- Soekmen, Ilkay,Ece, Abdulilah,Duez, Buelent,Sevin, Fatma
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experimental part
p. 650 - 653
(2010/06/16)
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- High ortho preference in Ni-catalyzed cross-coupling of halophenols with alkyl Grignard reagents
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(Chemical Equation Presented) High preference of substitution at the position ortho to the hydroxy group was observed for Ni-catalyzed cross-coupling reactions of dihalophenols with alkyl Grignard reagents. Reactions of 2,4-dihalophenols, with various com
- Wang, Jia-Rui,Manabe, Kei
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supporting information; experimental part
p. 741 - 744
(2009/08/07)
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- Mechanistic studies of the role of formaldehyde in the gas-phase methylation of phenol
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The gas-phase reaction between phenol and formaldehyde was studied using Bronsted acidic and basic catalysts to gain insight into the components of phenol methylation with methanol. Formaldehyde and methylformate form from methanol during phenol methylati
- Ballarini,Cavani,Maselli,Passeri,Rovinetti
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p. 215 - 225
(2008/09/21)
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- Synthesis of aromatic compounds using combinations of ring-closing olefin metathesis, dehydration, oxidation, and tautomerization
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An approach to aromatic compounds using combinations of ring-closing olefin metathesis (RCM), dehydration, oxidation, and tautomerization is reported. The RCM reaction of l,7-diene-3,5-diols, which were readily prepared by the allylation of aldol products, gave corresponding cyclized products, 4-cyclohexene-l,3-diols, in high yields. The subsequent dehydration or oxidation of 4-cyclohexene-1,3-diols led to versatile substituted benzenes including phenol and resorcinol derivatives.
- Yoshida, Kazuhiro,Toyoshima, Takeharu,Imamoto, Tsuneo
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scheme or table
p. 1512 - 1517
(2009/05/06)
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- Efficient synthetic routes to aromatic compounds using ring-closing olefin metathesis followed by dehydration, oxidation, and tautomerization
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A simple synthetic approach to aromatic compounds using combinations of RCM, dehydration, oxidation, and tautomerization is described. The Royal Society of Chemistry.
- Yoshida, Kazuhiro,Toyoshima, Takeharu,Imamoto, Tsuneo
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p. 3774 - 3776
(2008/03/12)
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- The transformations involving methanol in the acid- and base-catalyzed gas-phase methylation of phenol
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The alkylation of phenol with methanol was studied using a Bronsted-type acid catalyst (a H-mordenite) and basic/dehydrogenating catalysts (MgO, Fe2O3 and Mg/Fe/O), with the aim of investigating the reaction mechanism. The main difference between the two classes of catalysts concerned the transformations occurring on methanol. Specifically, in the former case the acid-type activation of methanol led to the development of an electrophylic species that gave rise to the formation of anisole and of C-alkylated compounds. With basic catalysts, methanol dehydrogenated to formaldehyde, which then underwent transformation to methylformate and to decomposition products, i.e., CO, CO2, CH4 and H2. In this case, the prevailing compounds obtained by reaction with phenol were o-cresol and 2,6-xylenol. The dehydrogenation of methanol was found to be the key-step in the generation of the active methylating species with basic catalysts.
- Ballarini,Cavani,Maselli,Montaletti,Passeri,Scagliarini,Flego,Perego
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p. 423 - 436
(2008/09/18)
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- Novel template-directed anodic phenol-coupling reaction
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Substituted phenols were anodically coupled to the corresponding 2,2'-biphenols via tetraphenoxy borate derivatives. This electrochemical method is particularly useful for methyl-substituted substrates, such as 2,4-dimethyl phenol. The selective ortho-coupling reaction can be easily performed on a multikilogram scale.
- Malkowsky, Itamar M.,Rommel, Christina E.,Froehlich, Roland,Griesbach, Ulrich,Puetter, Hermann,Waldvogel, Siegfried R.
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p. 7482 - 7488
(2007/10/03)
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- Metal ion promoted transesterifications of carboxylate esters. A structure/activity study of the efficacy of Zn2+ and La3+ to catalyze the methanolysis of some aryl and aliphatic esters
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The methanolysis of various aryl and aliphatic carboxylate esters promoted by methoxide, 1,5,9-triazacyclododecane: Zn2+(-OCH 3) and La3+(-OCH3), were studied and the derived rate constants (kOCH3, kcat 3:Zn(OCH3) and kcatLa(OCH3)) correlated in various ways. The metal ion catalyzed reactions are very much faster than the background reactions in some cases reaching up to 7 × 106-fold acceleration when present at concentrations of 5 mmol dm-3. The data for both metals exhibit non-linear Bronsted correlations with the pK a of the leaving group which are analyzed in terms of a change in rate limiting step from formation to breakdown of a metal-coordinated tetrahedral intermediate as the pKa increases above values of ~14.7. Plots of the log kOCH3 reaction vs. the log k cat, values for each metal ion indicate low sensitivity for aryl esters and a higher sensitivity for the aliphatic esters. A mechanistic rationale for the observations is presented.
- Neverov, Alexei A.,Sunderland,Brown, R. Stan
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- Leaving group effects on the mechanism of aromatic nucleophilic substitution (SnAr) reactions of some phenyl 2,4,6-trinitrophenyl ethers with aniline in acetonitrile
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Kinetic studies are reported for the reactions with aniline in acetonitrile of a series of X-phenyl 2,4,6trinitrophenyl ethers [X = H, 2-, 3-, 4-CH3,2,4-, 2,6-(CH3)2,2-, 3-, 4-NO 2,2,4-, 2,6-(NO2)2]. X-ray crystal structures for X = H, 2,6-(CH3)2 and 2,6-(NO2) 2 are reported and provide evidence for steric crowding around the 1-position of these molecules. Nevertheless, the kinetic data show that increasing substitution does not sterically inhibit nucleophilic attack by aniline and an 'early' transition state is likely. In general, the reactions are base catalysed; interpreted as rate-limiting deprotonation of the zwitterionic intermediates. Only with the dinitro derivatives is an uncatalysed reaction involving intramolecular proton transfer observed and when X = 2,6-(NO2)2 this pathway takes all the reaction flux. Copyright
- Crampton, Michael R.,Emokpae, Thomas A.,Howard, Judith A.K.,Isanbor, Chukwuemeka,Mondal, Raju
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