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All total 847 Articles be foundEfficient aryl-(hetero)aryl coupling by activation of C-Cl and C-F bonds using nickel complexes of air-stable phosphine oxides
Ackermann, Lutz,Born, Robert,Spatz, Julia H.,Meyer, Daniel
, p. 7216 - 7219 (2005)
(Chemical Equation Presented) A couple of couplings: Air-stable diamino-and dioxophosphine oxides are used as preligands in the nickel-catalyzed Kumada cross-coupling reactions of aryl Grignard reagents. A sterically hindered preligand allows for highly efficient cross-coupling of aryl fluorides at ambient temperature (acac = acetylacetonate).
Ortho-selective methylation of phenol catalyzed by CeO2-MgO prepared by citrate process
Sato, Satoshi,Koizumi, Kaoru,Nozaki, Fumio
, p. 264 - 274 (1998)
Vapor-phase alkylation of phenol with methanol was investigated over CeO2-MgO catalysts prepared utilizing a molten mixture of the corresponding nitrates and citric acid. The CeO2-MgO had attractive catalytic performance without decay of activities at the temperature range between 450 and 550°C, and it had excellent selectivities to the sum of o-cresol and 2,6-xylenol higher than 98%. The CeO2-MgO catalysts were found to be mixtures of MgO and an interstitial solid solution of MgxCe1-x/2O2 as a result of XRD measurement. It is confirmed that citric acid used in the preparation heightens the dispersion of the solid solution in the MgO matrix. The pure CeO2, which also exhibited efficient ortho-selectivity, had only weak basic sites in the TPD experiment of adsorbed CO2, while the pure MgO with strong basicity showed very low reaction rate in the methylation. The solid solution of MgxCe1-x/2O2 in the CeO2-MgO catalyst probably provides active centers for the methylation of phenol. In the results of methanol decomposition, methanol was converted into CO, CO2, and CH4 over the CeO2-MgO catalysts, without producing dimethyl ether. The reaction mechanism of the ortho-methylation over the CeO2-MgO catalyst is speculated: the ortho position of phenol adsorbed perpendicularly on weak basic sites on the MgxCe1-x/2O2 solid solution is selectively alkylated by methanol which is possibly activated in the form of formyl or hydroxy methyl group rather than methyl cation.
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Gilman et al.
, p. 2106 (1945)
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Ionic liquids as recyclable and separable reaction media in Rh-catalyzed decarbonylation of aromatic and aliphatic aldehydes
Malcho, Phillip,Garca-Surez, Eduardo J.,Riisager, Anders
, p. 58151 - 58155 (2014)
Ionic liquids (ILs) have been applied as recyclable reaction media in the decarbonylation of aldehydes in the presence of a rhodium-phosphine complex catalyst. The performance of several new catalytic systems based on imidazolium-based ILs and [Rh(dppp)2]Cl (dppp: 1,3-diphenylphosphinopropane) were excellent in the decarbonylation of both aromatic and aliphatic aldehydes providing >99 yield of benzenes and alkanes, respectively. The catalytic performance depended, however, strongly on the employed IL and its thermal stability. In addition, the ILs afforded good catalyst immobilization as well as a biphasic system with the product allowing recovery and reuse of the employed catalyst.
Fluoroform-derived CuCF3 for low-cost, simple, efficient, and safe trifluoromethylation of aryl boronic acids in air
Novak, Petr,Lishchynskyi, Anton,Grushin, Vladimir V.
, p. 7767 - 7770 (2012)
Easy does it: Aryl boronic acids undergo smooth and selective trifluoromethylation with low-cost fluoroform-derived CuCF3 in DMF in non-dried air. The reaction occurs under mild conditions (1 atm, room temperature), exhibits unprecedented funct
PdCl2-catalyzed hydrogenolysis of a C-O bond in monoaryl sulfates by sodium phosphinate in an aqueous alkaline medium
Davydov, D. V.,Beletskaya, I. P.
, p. 573 - 575 (1993)
The hydrogenolysis of the C-O bond in monoaryl sulfates by the action of an excess of NaH2PO2 in the presence of catalytic amounts of PdCl2 and KOH is studied.The reaction proceeds chemoselectively with complete ester conversion to the corresponding arenes.
Protodecarboxylation of benzoic acids under radical conditions
Seo, Sangwon,Taylor, John B.,Greaney, Michael F.
, p. 8270 - 8272 (2012)
A new approach to protodecarboxylation is described that enhances the substrate scope for benzoic acids. The reaction uses oxidative radical conditions to decarboxylate a variety of acids in acetonitrile.
Regioselective hydrogenolysis of aryl ether C-O bonds by tungsten carbides with controlled phase compositions
Fang, Huihuang,Du, Junmou,Tian, Chenchen,Zheng, Jianwei,Duan, Xinping,Ye, Linmin,Yuan, Youzhu
, p. 10295 - 10298 (2017)
Evenly dispersed tungsten carbides with controlled phase compositions that exhibit an impressive capacity to carry out the regioselective hydrogenolysis of inert aryl ether C-O bonds instead of aliphatic C-O bonds to produce aromatic compounds are reported.
Nucleophilic Photoreaction of Chlorobenzene in Methanol as Studied by Emission Spectroscopy
Nagaoka, Shin-ichi,Takemura, Takeshi,Baba, Hiroaki
, p. 2082 - 2087 (1985)
The photoreaction of chlorobenzene in methanol has been studied by means of emission spectroscopy.Upon irradiation with UV light, chlorobenzene reacts with methanol to form anisole with a quantum yield of 0.049 at 18 deg C.Contrary to the case of chlorobenzene, the photoreaction of p-dichlorobenzene with methanol is not observed.By combining these results with those of our recent studies on the dual phosphorescence from low-lying triplet states of halogenated benzenes, it is suggested that the photoreaction of chlorobenzene with methanol, which is a nucleophilic substitution reaction, occurs in the 3(?,?*) state.From the temperature dependence of the quantum yield, the activation energy for the nucleophilic photoreaction is estimated to be larger by about 3 - 4 kcal mol-1 than the apparent activation energy for a combination of the nonradiative 3(?,?*)->S0 process and the homolytic dissociative process concerning the C-Cl bond in the 3(?,?*) state.It is suggested that the nucleophilic photoreaction contrasts with the radical reaction leading to the dissociation of the C-Cl bond; the latter reaction occurs in the 3(?,?*) state as well as in the 3(?,?*) state.
Efficient Catalysis of Hydrodediazoniations in Dimethylformamide
Wassmundt, Frederick W.,Kiesman, William F.
, p. 1713 - 1719 (1995)
For hydrodediazoniations (the replacement of a diazo group by hydrogen) in DMF, several substances act as catalysts through their ability to serve as electron donors and initiate free-radical reactions.A general procedure has been developed in which FeSO4 speeds the conversion and leads to higher yields.Trapping experiments demonstrated the presence of free-radical intermediates.N,N-Dimethylacetamide was found to rival DMF as a source of hydrogen atoms.
A Biomass-Derived Non-Noble Cobalt Catalyst for Selective Hydrodehalogenation of Alkyl and (Hetero)Aryl Halides
Sahoo, Basudev,Surkus, Annette-Enrica,Pohl, Marga-Martina,Radnik, J?rg,Schneider, Matthias,Bachmann, Stephan,Scalone, Michelangelo,Junge, Kathrin,Beller, Matthias
, p. 11242 - 11247 (2017)
Hydrodehalogenation is a straightforward approach for detoxifications of harmful anthropogenic organohalide-based pollutants, as well as removal of halide protecting groups used in multistep syntheses. A novel sustainable catalytic material was prepared from biowaste (chitosan) in combination with an earth-abundant cobalt salt. The heterogeneous catalyst was fully characterized by transmission electron microscope, X-ray diffraction, and X-ray photoelectron spectroscopy measurements, and successfully applied to hydrodehalogenation of alkyl and (hetero)aryl halides with broad scope (>40 examples) and excellent chemoselectivity using molecular hydrogen as a reductant. The general usefulness of this method is demonstrated by successful detoxification of non-degradable pesticides and fire retardants. Moreover, the potential of the catalyst as a deprotection tool is demonstrated in a multistep synthesis of (±)-peronatin B (alkaloid).
Hydrodeoxygenation of guaiacol over carbon-supported metal catalysts
Chang, Jie,Danuthai, Tanate,Dewiyanti, Silvia,Wang, Chuan,Borgna, Armando
, p. 3041 - 3049 (2013)
Catalytic bio-oil upgrading to produce renewable fuels has attracted increasing attention in response to the decreasing oil reserves and the increased fuel demand worldwide. Herein, the catalytic hydrodeoxygenation (HDO) of guaiacol with carbon-supported non-sulfided metal catalysts was investigated. Catalytic tests were performed at 4.0MPa and temperatures ranging from 623 to 673K. Both Ru/C and Mo/C catalysts showed promising catalytic performance in HDO. The selectivity to benzene was 69.5 and 83.5% at 653K over Ru/C and 10Mo/C catalysts, respectively. Phenol, with a selectivity as high as 76.5%, was observed mainly on 1Mo/C. However, the reaction pathway over both catalysts is different. Over the Ru/C catalyst, the O-CH3 bond was cleaved to form the primary intermediate catechol, whereas only traces of catechol were detected over Mo/C catalysts. In addition, two types of active sites were detected over Mo samples after reduction in H2 at 973K. Catalytic studies showed that the demethoxylation of guaiacol is performed over residual MoOx sites with high selectivity to phenol whereas the consecutive HDO of phenol is performed over molybdenum carbide species, which is widely available only on the 10Mo/C sample. Different deactivation patterns were also observed over Ru/C and Mo/C catalysts.
The mechanism of phenol methylation on acid and basic zeolite catalysts
Borodina,Pomakhina,Ramishvili,Ponomareva,Rebrov,Ivanova
, p. 892 - 898 (2006)
The alkylation of phenol with methanol on HY and CsY/CsOH catalysts was studied in situ under static conditions by 13C NMR spectroscopy. Attention was largely given to the identification of intermediate compounds and mechanisms of anisole, cresol, and xylenol formation. The mechanisms of phenol methylation were found to be different on acid and basic catalysts. The primary process on acid catalysts was the dehydration of methanol to dimethyl ether and methoxy groups. This resulted in the formation of anisole and dimethyl ether, the ratio between which depended on the reagent ratio, which was evidence of similar mechanisms of their formation. Subsequent reactions with phenol gave cresols and anisoles. Cresols formed at higher temperatures both in the direct alkylation of phenol and in the rearrangement of anisole. The main alkylation product on basic catalysts was anisole formed in the interaction of phenolate anions with methanol; no cresol formation was observed. The deactivation of acid catalysts was caused by the formation of condensed aromatic hydrocarbons that blocked zeolite pores. The deactivation of basic catalysts resulted from the condensation of phenol and formaldehyde with the formation of phenol-formaldehyde resins. Nauka/Interperiodica 2006.
Reactivity in cleavage of dimethoxybenzenes by sodium in liquid ammonia
Bunnett, Joseph F.,Jenvey, Judy
, p. 8069 - 8073 (1996)
The sodium/liquid ammonia cleavage of the dimethoxybenzenes and related substances, reported in large part by Birch in 1947, has been re-examined with use of improved techniques. Remarkable patterns of reactivity (e.g., ortho > meta ? para) that he described are confirmed and extended. They are agreeably rationalized by means of a simple, approximate adaptation from MO theory.
Transfer hydrodehalogenation of aryl halides accelerated by a saturated sodium acetate aqueous solution
Xue, Zhimin,Zhao, Xinhui,Wang, Jinfang,Mu, Tiancheng
, p. 102193 - 102197 (2016)
Development of catalytic hydrodehalogenation of halogenated organic compounds is an important topic from the viewpoint of environment protection. Herein, we conducted the first work on the utilization of a saturated aqueous solution of sodium acetate (CH3COONa) as an efficient and environmentally-friendly reaction medium for transfer hydrodehalogenation of various aryl halides using Pd/C as the catalyst. It was found that the transfer hydrodehalogenation could be accelerated significantly by the saturated CH3COONa aqueous solution due to the surfactant-similar effect of CH3COONa and the activation of the C-Cl bond by the dissolved solvated ions.
Preparation of aromatic amines by copper-catalyzed coupling of boronic acids with aqueous ammonia
Jiang, Zhaoqiong,Wu, Zhiqing,Wang, Lixia,Wu, Di,Zhou, Xiangge
, p. 964 - 968 (2010)
A simple, highly efficient, and environmentally friendly protocol for the synthesis of primary aromatic amines by catalytic coupling of aromatic boronic acids with aqueous ammonia has been developed by using commercial and inexpensive CuSO4·5H2O as catalyst without addition of other solvents under mild reaction conditions.
Efficient Decarbonylation of Furfural to Furan Catalyzed by Zirconia-Supported Palladium Clusters with Low Atomicity
Ishida, Tamao,Kume, Kurumi,Kinjo, Kota,Honma, Tetsuo,Nakada, Kengo,Ohashi, Hironori,Yokoyama, Takushi,Hamasaki, Akiyuki,Murayama, Haruno,Izawa, Yusuke,Utsunomiya, Masaru,Tokunaga, Makoto
, p. 3441 - 3447 (2016)
Decarbonylation of furfural to furan was efficiently catalyzed by ZrO2-supported Pd clusters in the liquid phase under a N2atmosphere without additives. Although Pd/C and Pd/Al2O3have frequently been used for decarbonylation, Pd/ZrO2exhibited superior catalytic performance compared with these conventional catalysts. Transmission electron microscopy and X-ray absorption fine structure measurements revealed that the size of the Pd particles decreased with an increase in the specific surface area of ZrO2. ZrO2with a high surface area immobilized Pd as clusters consisting of several (three to five) Pd atoms, whereas Pd aggregated to form nanoparticles on other supports such as carbon and Al2O3despite their high surface areas. The catalytic activity of Pd/ZrO2was enhanced with a decrease in particle size, and the smallest Pd/ZrO2was the most active catalyst for decarbonylation. When CeO2was used as the support, a decrease in Pd particle size with an increase in surface area was also observed. Single Pd atoms were deposited on CeO2with a high surface area, with a strong interaction through the formation of a Pd?O?Ce bond, which led to a lower catalytic activity than that of Pd/ZrO2. This result suggests that zero-valent small Pd clusters consisting of more than one Pd atom are the active species for the decarbonylation reaction. Recycling tests proved that Pd/ZrO2maintained its catalytic activity until its sixth use.
Base-promoted protodeboronation of 2,6-disubstituted arylboronic acids
Lozada, Jerome,Liu, Zhibo,Perrin, David M.
, p. 5365 - 5368 (2014)
Facile based promoted deboronation of electron-deficient arylboronate esters was observed for arylboronates containing two ortho electron-withdrawing group (EWG) substituents. Among 30 representative boronates, only the diortho-substituted species underwe
Homolytic C-S bond scission in the desulfurization of aromatic and aliphatic thiols mediated by a Mo/Co/S cluster: Mechanistic aspects relevant HDS catalysis
Curtis, M. David,Druker, Scott H.
, p. 1027 - 1036 (1997)
The kinetics of the reaction of a series of aromatic and aliphatic thiols with cluster 1 were determined. These reactions form cluster 2 and the arene or alkane corresponding to the thiol: Cp'2Mo2Co2S3(CO)4 (1) + RSH → Cp'2Mo2Co2S4(CO)2 (2) + RH + 2CO. These reactions are first order in thiol and first order in cluster 1 with appreciable negative entropies of activation. These data suggest that the rate determining step of the desulfurization reaction is the initial association of the thiol to the cluster. The more nucleophilic thiolate anions react with 1 at -40°C to form an adduct in which the thiolate anion is bound η1 to the Co atom. At -25°C, the initial adduct rearranges to a fluxional μ2, η1-bound thiolate. The fluxional process is proposed to involve a concerted 'walking' of the thiolate and a μ2-bound sulfide ligand on the surface of the cluster. Near 35°C, the thiolate-cluster adduct undergoes C-S bond homolysis to give the paramagnetic anion of cluster 1 and the phenyl or alkyl radical. The radical nature of the C-S bond cleavage was confirmed by the desulfurization of the radical clock reagents, cyclopropylmethanethiol and -thiolate anion, that form the cyclopropylmethyl radical which rearranged to the butenyl radical. The possible similarity in the C-S bond cleavage mechanism in these desulfurization reactions to those occurring in hydrodesulfurization (HDS) over Co/Mo/S catalysts is discussed.
The Mechanism of Titanium Complex-Catalyzed Reduction of Aryl Halides by Sodium Borohydride Is Strongly Solvent Dependent
Liu, Yumin,Schwartz, Jeffrey
, p. 940 - 942 (1994)
The titanium complex-catalyzed reduction of aryl halides by sodium borohydride in dimethylacetamide (DMA) or ethers proceeds by electron transfer from a reduced titanium species, yielding an intermediate aryl radical.
Birch, A. J.,Cross, P.E.,Fitton, H.
, (1965)
Liquid chromatography-photolysis-electrochemical detection for organoiodides. 2. Operative mechanisms.
Selavka,Krull
, p. 2704 - 2709 (1987)
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Stannylated Vinylic addition polynorbornene: Probing a reagent for friendly tin-mediated radical processes
García-Loma, Rodrigo,Alb é Niz, Ana C.
, p. 4247 - 4254 (2017)
Vinylic addition polynorbornenes (VA-PNB) with stannyl functional groups have been prepared and used in tinmediated radical dehalogenation reactions. The aliphatic and robust scaffold of VA-PNB is well suited for a support in radical processes. VA-PNB-(CH2)nSnHBu2 can be used as a stoichiometric reagent and VA-PNB-(CH2)nSnBu2Cl as a catalyst in the presence of a hydride donor for the reduction of RBr. The mixture KF (aq.)/polymethylhydrosiloxane (PMHS) is the most convenient hydride source to generate VA-PNB-(CH2)nSnHBu2 in situ. Al-though quite popular in this context, boron hydrides, being a source of radicals themselves, are not adequate to correctly evaluate the performance of the anchored organotin group. VAPNB-(CH2)4SnBu2Cl can be recycled and, even if it loses activity upon reuse, it is still useful after ten cycles. The stannylated VAPNB can be separated from the products by simple filtration, and it leads to very low tin contamination (at least 250 times lower than that with use of conventional separation methods).
Role of copper- or cerium-promoters on NiMo/Γ-Al2O3 catalysts in hydrodeoxygenation of guaiacol and bio-oil
Sangnikul, Patiphat,Phanpa, Chanisara,Xiao, Rui,Zhang, Huiyan,Reubroycharoen, Prasert,Kuchonthara, Prapan,Vitidsant, Tharapong,Pattiya, Adisak,Hinchiranan, Napida
, p. 151 - 160 (2019)
Effect of copper (Cu) or cerium (Ce) as promoters for nickel-molybdenum/γ-alumina (NiMo/γ-Al2O3) catalyst on the hydrodeoxygenation (HDO) of guaiacol (GUA), a model oxygenated compound found in a bio-oil derived from woody biomass, was comparatively investigated. The addition of Cu- or Ce-promoters affected the physicochemical properties of the NiMo catalyst. The NiMo catalyst promoted by Cu showed the higher reducibility, whilst the Ce-promoter (2–8 wt% based on γ-Al2O3 content) provided the NiMo catalyst with a higher distribution of active metals and induced a greater difficulty in the reduction under hydrogen (H2) atmosphere. For the HDO of GUA at a mild reaction condition (10 bar initial H2 pressure and 300 °C) in the absence of solvent, the Cu-promoter enhanced the hydrogenation activity of the NiMo catalyst to convert GUA to phenol and methylphenols, one-atomic oxygen species. Whereas, the addition of Ce obviously inhibited the formation of coke on the catalyst surface after a long reaction period (6 h) and gave a higher GUA conversion level with increasing yield of phenols. For the HDO of real bio-oil obtained from the fast pyrolysis of cassava rhizome, the NiMo catalysts promoted by Cu or Ce at 4 wt% based on the γ-Al2O3 content showed a higher performance at eliminating the oxygenated compounds in the bio-oil, reducing the oxygen/carbon (O/C) molar ratio by over seven-fold from 1.75 to 0.24–0.25. Moreover, the gross heating value of the bio-oil was improved from 21.5 to ca. 29.0 MJ/kg after the HDO process. However, the addition of the Cu or Ce promoter did not inhibit coke deposition, possibly due to the acidic properties of the bio-oil that deteriorated the catalyst performance by metal leaching.
Continuous in situ generation, separation, and reaction of diazomethane in a dual-channel microreactor
Maurya, Ram Awatar,Park, Chan Pil,Lee, Jang Han,Kim, Dong-Pyo
, p. 5952 - 5955 (2011)
A fierce dog: A method for the continuous in-situ on-demand generation, separation, and reaction of diazomethane in a dual-channel microreactor has been developed (see picture; Diazald=N-methyl-N-nitroso-p-toluenesulfonamide). The microchemical system allows a variety of diazomethane reactions to be performed without the most common problems of preparation, handling, transfer, and decomposition.
Highly Selective Hydrodeoxygenation of Lignin to Naphthenes over Three-Dimensional Flower-like Ni2P Derived from Hydrotalcite
Chen, Guanyi,Diao, Xinyong,Ji, Na,Jia, Zhichao,Li, Changzhi,Li, Xinxin,Liu, Caixia,Liu, Qingling,Lu, Xuebin,Ma, Longlong,Song, Chunfeng,Wang, Shurong,Zhao, Yujun
, p. 1338 - 1356 (2022/02/07)
A strategy for low-temperature synthesis of hydrotalcite-based nickel phosphide catalysts (Ni2P-Al2O3) with flower-like porous structures was proposed. The in situ reduction of red phosphorus at 500 °C enables Ni2P catalysts with small particle size and abundant active and acidic sites, which facilitate the activation of substrates and H2. In the hydrodeoxygenation of guaiacol, a 100% conversion and 94.5% yield of cyclohexane were obtained over the Ni2P-Al2O3 catalyst under 5 MPa H2 at 250 °C for 3 h. Other lignin-derived phenolic compounds could also afford the corresponding alkanes with yields higher than 85%. Moreover, Ni2P-Al2O3 exhibited high hydrodeoxygenation activity in the deconstruction of more complex wood structures, including lignin oil and real lignin. Among the two different types of Ni sites of Ni(1) and Ni(2) in Ni2P, density functional theory (DFT) calculations showed that the Ni(2) site, highly exposed on the Ni2P-Al2O3 surface, possesses a stronger ability to break C-OH bonds during the hydrodeoxygenation of guaiacol in comparison with the Ni(1) site.
Protodesilylation of Arylsilanes by Visible-Light Photocatalysis
García Manche?o, Olga,Kuhlmann, Jan H.,Uygur, Mustafa
supporting information, p. 1689 - 1694 (2022/03/14)
The first visible-light-mediated photocatalytic, metal- and base-free protodesilylation of arylsilanes is presented. The C(sp2)-Si bond cleavage process is catalyzed by a 5 mol % loading of a commercially available acridinium salt upon blue-light irradiation. Two simple approaches have been identified employing either aerobic or hydrogen atom transfer cocatalytic conditions, which enable the efficient and selective desilylation of a broad variety of simple and complex arylsilanes under mild conditions.
Design of an Electron-Withdrawing Benzonitrile Ligand for Ni-Catalyzed Cross-Coupling Involving Tertiary Nucleophiles
Edjoc, Racquel K.,Mills, L. Reginald,Rousseaux, Sophie A. L.
supporting information, p. 10422 - 10428 (2021/07/26)
The design of new ligands for cross-coupling is essential for developing new catalytic reactions that access valuable products such as pharmaceuticals. In this report, we exploit the reactivity of nitrile-containing additives in Ni catalysis to design a benzonitrile-containing ligand for cross-coupling involving tertiary nucleophiles. Kinetic and Hammett studies are used to elucidate the role of the optimized ligand, which demonstrate that the benzonitrile moiety acts as an electron-acceptor to promote reductive elimination over β-hydride elimination and stabilize low-valent Ni. With these conditions, a protocol for decyanation-metalation and Ni-catalyzed arylation is conducted, enabling access to quaternary α-arylnitriles from disubstituted malononitriles.
