- Catalytic Oxidative Cracking of Benzene Rings in Water
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Efficient degradation of harmful benzene rings in water is indispensable for achieving a clean water environment. We report herein unprecedented catalytic oxidative benzene cracking (OBC) in water using a ruthenium(II)-aqua complex having an N-heterocyclic carbene ligand as a catalyst and a cerium(IV) salt as a sacrificial oxidant under mild conditions. The OBC reactions produced carboxylic acids such as formic acid, which can be converted to dihydrogen directly from the OBC solution using a rhodium(III) catalyst with adjustment of the solution pH to 3.3. The OBC reactions can be applied to monosubstituted benzene derivatives such as ethylbenzene, chlorobenzene, and benzoic acid. Initial rates of the OBC reactions showed a linear relationship in the Hammett plot with a negative slope, indicating the electrophilicity of a Ru(III)-oxyl complex as the reactive species in the catalytic OBC reaction. Also, we discuss a plausible mechanism of the catalytic OBC reactions based on the kinetic analysis and the product stoichiometry for the OBC reaction of nonvolatile sodium m-xylene sulfonate. The addition of an electrophilic radical to the aromatic ring to form arene oxide/oxepin is proposed as the initial step of the OBC reaction.
- Shimoyama, Yoshihiro,Ishizuka, Tomoya,Kotani, Hiroaki,Kojima, Takahiko
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p. 671 - 678
(2019/01/08)
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- Lewis Acid-Catalyzed Reductive Amination of Aldehydes and Ketones with N,N-Dimethylformamide as Dimethylamino Source, Reductant and Solvent
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A practical zinc acetate dihydrate-catalyzed reductive amination of various carbonyl compounds with N,N-dimethylformamide (DMF) as dimethylamino (Me2N) source, reductant and solvent has been developed. This reaction shows broad substrate scope,
- Yang, Luo,Lin, Jie,Kang, Lei,Zhou, Wang,Ma, Da-You
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supporting information
p. 485 - 490
(2018/01/15)
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- SELECTIVE CARBON-CARBON BOND CLEAVAGE BY EARTH ABUNDANT VANADIUM COMPOUNDS UNDER VISIBLE LIGHT PHOTOCATALYSIS
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Provided herein a vanadium(V) complex of formula I, where R1 to R8 are as defined herein. Also provided herein are reactions making use of the vanadium(V) complex of formula I, such as selective sp3-sp3 carbon-carbon bond cleavage under visible light photocatalysis and photodegradation of lignin.
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Page/Page column 48
(2016/09/22)
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- Silicone wastes as reducing agents for carbon dioxide transformation: Fluoride-catalyzed formic acid synthesis from CO2, H2O, and disilanes
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Disilanes were found to be reactive reducing agents for the transformation of carbon dioxide to formic acid in the presence of H2O. The reaction is catalyzed by fluoride salts such as tetrabutylammonium fluoride. Isotopic experiments revealed that the proposed reaction pathway includes Si-Si bond cleavage to afford hydrosilane followed by the hydrosilylation of CO2, and, finally, the hydrolysis of silyl formate.
- Motokura, Ken,Naijo, Masaki,Yamaguchi, Sho,Miyaji, Akimitsu,Baba, Toshihide
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supporting information
p. 1464 - 1466
(2015/11/24)
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- Selective photocatalytic C-C bond cleavage under ambient conditions with earth abundant vanadium complexes
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Selective C-C bond cleavage under ambient conditions is a challenging chemical transformation that can be a valuable tool for organic syntheses and macromolecular disassembly. Herein, we show that base metal vanadium photocatalysts can harvest visible light to effect the chemoselective C-C bond cleavage of lignin model compounds under ambient conditions. Lignin, a major aromatic constituent of non-food biomass, is an inexpensive, accessible source of fine chemical feedstocks such as phenols and aryl ethers. However, existing lignin degradation technologies are harsh and indiscriminately degrade valuable functional groups to produce intractable mixtures. The selective, photocatalytic depolymerization of lignin remains underexplored. In the course of our studies on lignin model compounds, we have uncovered a new C-C activation reaction that takes place under exceptionally mild conditions with high conversions. We present our fundamental studies on representative lignin model compounds, with the aim of expanding and generalizing the substrate scope in the future. Visible light is employed in the presence of earth-abundant vanadium oxo catalysts under ambient conditions. Selective C-C bond cleavage leads to valuable and functionally rich fine chemicals such as substituted aryl aldehydes and formates. Isotope labeling experiments, product analyses, and intermediate radical trapping, together with density functional theory studies, suggest a unique pathway that involves a photogenerated T1 state during the C-C bond cleavage reactions. Our study demonstrates a sustainable approach to harvest sunlight for an unusual, selective bond activation, which can potentially be applied in organic transformations and biomass valorization.
- Gazi, Sarifuddin,Hung Ng, Wilson Kwok,Ganguly, Rakesh,Putra Moeljadi, Adhitya Mangala,Hirao, Hajime,Soo, Han Sen
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p. 7130 - 7142
(2015/11/24)
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- Comparison of homogeneous and heterogeneous catalysts for glucose-to-fructose isomerization in aqueous media
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Herein, the first comparison of the mechanisms of glucose-to-fructose isomerization in aqueous media enabled by homogeneous (CrCl3 and AlCl3) and heterogeneous catalysts (Sn-beta) by using isotopic-labeling studies is reported. A pronounced kinetic isotope effect (KIE) was observed if the deuterium label was at the C2 position, thus suggesting that a hydrogen shift from the C2 to C1 positions was the rate-limiting step with the three catalysts. 13C and 1HNMR spectroscopic investigations confirmed that an intra-hydride-transfer reaction pathway was the predominant reaction channel for all three catalysts in aqueous media. Furthermore, the deuterium atom in the labeled glucose could be mapped onto hydroxymethylfurfural and formic acid through reactions that followed the isomerization step in the presence of Br?nsted acids. In all three catalysts, the active site appeared to be a bifunctional Lewis-acidic/ Br?nsted-basic site, based on a speciation model and first-principles calculations. For the first time, a mechanistic similarities between the homogeneous and heterogeneous catalysis of aldose-to-ketose isomerization is established and it is suggested that learning from homogeneous catalysis could assist in the development of improved heterogeneous catalysts. Different strokes: Isotopic-labeling experiments reveal mechanistic similarities between homogeneous and heterogeneous catalysts for the aldose-to-ketose isomerization reaction in aqueous media. An intra-hydride transfer is the dominant reaction channel for the isomerization and a Lewis acid-Br?nsted base bifunctional site is the most active site for all three catalysts. Copyright
- Choudhary, Vinit,Pinar, Ana B.,Lobo, Raul F.,Vlachos, Dionisios G.,Sandler, Stanley I.
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p. 2369 - 2376
(2014/01/06)
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- Oxygen-independent decarbonylation of aldehydes by cyanobacterial aldehyde decarbonylase: A new reaction of diiron enzymes
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Just add water: Structurally, cyanobacterial aldehyde decarbonylases are members of the non-heme diiron oxygenase family of enzymes. However, the enzyme catalyzes the hydrolysis of aliphatic aldehydes to alkanes and formate (see scheme), in an oxygen-independent reaction. This unusual and chemically difficult reaction most likely involves free radical intermediates. Copyright
- Das, Debasis,Eser, Bekir E.,Han, Jaehong,Sciore, Aaron,Marsh, E. Neil G.
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supporting information; experimental part
p. 7148 - 7152
(2011/09/30)
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- Effect of Reactivity on Virtual Transition-State Structure for the Acylation Stage of Acetylcholinesterase-Catalyzed Hydrolysis of Aryl Esters and Anilides
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The acylation stage of acetylcholinesterase-catalyzed hydrolysis of p-methoxyphenyl formate and of three anilides (o-nitrochloroacetanilide, o-nitroacetanilide, and o-nitroformanilide) has been studied by measuring substrate secondary and solvent isotope effects and by determining pL (L = H, D)-rate profiles and Eyring plots.The results of each of these probes support a model for acylation rate determination that involves a virtual transition state that contains contributions from the transition states of sequential physical and chemical steps.Eyring plots for all substrates are nonlinear and are interpreted in terms of temperature-dependent changes in fractional rate determination of sequential microscopic steps.For all substrates acylation reactivity increases sigmoidally with pH and depends on pKaH2O = 5.6-5.8, which is well below the intrinsic pKa = 6.3 of the active site histidine.Solvent isotope effects for the anilide substrates are in the range 1.3-1.6.Proton inventory experiments indicate that intrinsic solvent isotope effects of ca 2 that arise from general acid-base stabilization of the chemical transition state partially masked by a solvent isotope-insensitive transition state that contributes 58-67percent to acylation rate determination.For the most reactive substrate, p-methoxyphenyl formate, the solvent isotope effect is 1.09, which indicates that the solvent isotope-insensitive transition state is almost entirely rate determining.Substrate secondary deuterium kinetic isotope effects are consistent with decreasing nucleophilic interaction at the carbonyl carbon of the scissile bond of the substrate in the virtual acylation transition state with increasing kcat/Km.Hence, both solvent and substrate isotope effects indicate a general trend toward less acylation rate determination by chemical transition states as reactivity increases.The virtual transition-state model delineated herein lends quantitative support to Rosenberry's notion that the acylation stage of acetylcholinesterase-catalyzed hydrolysis of neutral substrates is prominently rate limited by an induced fit conformation change that precedes chemical catalysis.
- Acheson, Scott A.,Barlow, Paul N.,Lee, Gerald C.,Swanson, Michael L.,Quinn, Daniel M.
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p. 246 - 252
(2007/10/02)
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