3979-51-9Relevant academic research and scientific papers
Regularities of Pd/C-catalyzed reduction of trichlorobiphenyls with 2-propanol in basic medium
Kostenko,Eliseenkov,Petrov
, p. 1656 - 1662 (2017/09/25)
Reduction of a series of trichlorobiphenyls with 2-propanol in basic medium catalyzed by Pd/C has been studied. Regioselectivity of the reduction has been determined. In the studied cases, the chlorine atom in para or meta positions of the more substituted ring has been more reactive. Using isotope labeling, it has been demonstrated that the reaction occurs via the stage of 2-propanol dehydration on palladium catalyst, followed by catalytic hydrogenation of the polychlorinated biphenyls.
Imbalanced tunneling ready states in alcohol dehydrogenase model reactions: Rehybridization lags behind H-tunneling
Hammann, Blake,Razzaghi, Mortezaali,Kashefolgheta, Sadra,Lu, Yun
supporting information, p. 11337 - 11339 (2013/01/15)
The secondary kinetic isotope effects for the hydride transfer reactions from aliphatic alcohols to two carbocations (NAD+ models) in acetonitrile were determined. The results suggest that the hydride transfer takes place by tunneling and that the rehybridizations of both donor and acceptor carbons lag behind the H-tunneling. This is quite contrary to the observations in alcohol dehydrogenases where the importance of enzyme motions in catalysis is manifested.
Homogeneous catalytic oxidation of light alkanes: C-C bond cleavage under mild conditions
Chepaikin,Bezruchenko,Menchikova,Moiseeva,Gekhman
body text, p. 666 - 671 (2011/02/16)
The combined oxidation of CO and C2-C4 alkanes (associated petroleum gas and natural gas components) under the action of oxygen in trifluoroacetic acid solutions in the presence of rhodium and copper chlorides was accompanied by the oxidative degradation of C-C bonds in a hydrocarbon chain with the formation of carbonyl compounds, alcohols, and esters. For butane and isobutane, the reaction path with C-C bond cleavage was predominant. The buildup curves of isobutane oxidation products (both with the retention and with the degradation of the chain) were S-shaped and characterized by the same induction period; they did not pass through a maximum. A reaction scheme was proposed to reflect the main special features of the mechanism of transformations occurring in the O2/Rh/Cu/Cl- oxidation system.
Alkyl radical generation in water under ambient conditions - A new look at the Guareschi reaction of 1897
Nguyen, Bao,Chernous, Katya,Endlar, Daniel,Odell, Barbara,Piacenti, Michela,Brown, John M.,Dorofeev, Alexander S.,Burasov, Alexander V.
, p. 7655 - 7658 (2008/09/18)
(Chemical Equation Presented) Chemical and biochemical significance of a long-forgotten 19th century observation: The hydrocarbon production from quaternary glutarimides on neutralization in water is the consequence of formation of alkyl radicals, which means that it is possible to generate alkyl radicals under very mild conditions. Oxygen trapping competes with hydrogen abstraction (see scheme).
Inherent asymmetry of constitutionally equivalent methyl groups in the H/D equilibration of n- and i-C3H7Fe(OH)+ complexes
Trage, Claudia,Zummack, Waltraud,Schroeder, Detlef,Schwarz, Helmut
, p. 2708 - 2710 (2007/10/03)
Transiently formed, constitutionally identical methyl groups remain inequivalent in the course of an n-propyl?isopropyl isomerization (see scheme) operative in Fe÷-mediated dehydration of propanols. The reversibility of the β-hydrogen transfer steps is addressed by examination of the H/D equilibration in metastable complexes of Fe+ with a set of selectivity deuterated propanols by using tandem mass spectrometry.
Catalysis of transesterification reactions by lanthanides - Unprecedented acceleration of methanolysis of aryl and alkyl esters promoted by La(OTf)3 at neutral sspH and ambient temperatures
Neverov, Alexei A.,McDonald, Todd,Gibson, Graham,Brown
, p. 1704 - 1710 (2007/10/03)
La3+ catalysis of the methanolysis of the esters p-nitrophenyl, 2,4-dinitrophenyl, and phenyl acetate (1-3), phenyl benzoate (4), and ethyl, i-propyl, cyclohexyl, and tert-butyl acetate (5, 6a, 6b, 7) was studied at 25°C as a function of sspH and [La(OTf)3]. The active form of the catalyst is attributed to a dimethoxy-bridged dimer of stoichiometry (La3+)2(-OCH3)2, having maximum activity atsspH 8 to 9. For preparative reactions, the active catalyst can be made in situ simply by adding 0.01 equiv of La(OTf)3, and 0.01 equiv of NaOCH3 to a methanol solution containing the ester (1 M). Strong catalysis of methanolysis of both aryl and alkyl esters was observed, although tert-butyl acetate was inert. At sspH 8.5, where the catalyst is maximally active, the transesterification reactions are accelerated by 40 000-fold to 18 000 000-fold in the presence of as little as 5 mM catalyst relative to the background reaction depending on the ester structure. A mechanism for catalysis of transesterification is presented wherein the reactive species is generated by breaking a single La-OCH3 bond of the dimethoxy-bridged dimer to reveal a nucleophilic metal-bound methoxide - Lewis acid La3+ electrophilic pair.
Study of the mechanism for the hydrolysis of alkoxy(aryl)(phenyl)-λ6- sulfanenitriles, ArPhS(OR)(?N)
Yoshimura, Toshiaki,Dong, Tiaoling,Fujii, Takayoshi,Ohkubo, Masanori,Sakuta, Mikiko,Wakai, Youko,Ono, Shin,Morita, Hiroyuki,Shimasaki, Choichiro
, p. 957 - 965 (2007/10/03)
The hydrolysis of alkoxy(aryl)(phenyl)-λ6-sulfanenitriles in several buffer solutions was found to follow a good pseudo-first-order kinetic equation, giving the corresponding sulfoximides and alcohols (for the case of the hydrolysis of neopentyloxy-λ6-sulfanenitrile, giving a rearranged product, 2-methyl-2-butanol). The dependence of the rate of hydrolysis on the structure of the alkyl group showed the opposite trend to the usual S(N)2 character, i.e. Me +] at pH more than 6.08, and trends to saturate at low pH. According to these kinetic results, a two-step reaction mechanism was proposed which involves a pre-equilibrium protonation on the nitrogen atom of the alkoxy-λ6- sulfanenitriles, followed by a rate-determining C-O bond cleavage via an S(N)2 or S(N)1 mechanism on the alkyl carbon atom depending on the structure of the alkyl group. From a double-reciprocal plot of 1/k(obs) vs. 1/[H+], the pK(a) value and the rate constant of the second reaction of neopentyloxy(diphenyl)-λ6-sulfanenitrile were estimated to be 5.02 and 7.02x10-3 s-1, respectively. The substituent effects on the phenyl group of neopentyloxy(diphenyl)-λ6-sulfanenitrile afforded a large negative p- value (-1.88) for pK(a) and positive one (+1.66) for the second reaction at 25.2 °C. The small negative p-values observed at pH 6.27 for diphenyl(propoxy)-λ6-sulfanenitrile (-0.42) and neopentyloxy(diphenyl)- λ6-sulfanenitrile (-0.26) were found to be the results of a cancellation of those for the opposite trend of the reactions of the pre-equilibrium and the second step. The activation parameters for both the pre-equilibrium and the subsequent reactions were also estimated based on the parameters for the hydrolysis of neopentyloxy(diphenyl)-λ6-sulfanenitrile at pH 6.22 and 2.99. The buffer effect is due to a nucleophilic attack of the buffer base to the alkyl carbon atom of the protonated alkoxy-λ6-sulfanenitriles. The sulfoximide moiety in the protonated λ6-sulfanenitrile is revealed to be a very good leaving group.
Coenzyme F430 from Methanogenic Bacteria: Mechanistic Studies on the Reductive Cleavage of Sulfonium Ions Catalyzed by F430 Pentamethyl Ester
Lin, Shu-Kun,Jaun, Bernhard
, p. 1478 - 1490 (2007/10/02)
Mechanistic questions regarding the reductive cleavage of sulfonium ions by the NiI form of coenzyme F430 pentamethylester (F430M) were adressed in a series of kinetic studies and isotope labeling experiments.In neat DMF, methane formation from Dialkyl(methyl)sulfonium ions consistently showed a delay time of ca. 1 h.In the presence of excess propanethiol, no delay was observed and methane formation followed pseudo-first-order kinetics with a logarithmic dependence of the initial rate on the concentration of propanethiol.From the temperature dependence of the reaction rate, an estimate for the activation parameters ΔH(excit.) = 49 kJ mol-1 and (apparent) ΔS(excit.) = -114 J K-1 mol-1 was derived.The observation of deuterium incorporation into methane from (CH3)2CHOD, but not from (CH3)2CDOH, indicates that the fourth H-entity is introduced into CH4 as a proton, and that free CH3 radicals are not involved.In contrast to the reaction with the homogeneous one-electron reductant sodium naphthalide, the F430M-catalyzed reduction of mixed dialkyl(methyl)sulfonium ions showed a pronounced selectivity for the cleavage of Me-S over that of alkyl-S (alkyl Me) bonds.Mechanisms that are consistent with these results, as well as possible explanations for the time delay and the apparent highly negative entropy of activation, are discussed.
Mechanism of 2-Propanol Dehydrogenation with Suspended Nickel Fine-Particle Catalyst
Yamashita, Masaru,Dai, Feng-Yuen,Suzuki, Minoru,Saito, Yasukazu
, p. 628 - 634 (2007/10/02)
Selective dehydrogenation of 2-propanol was performed with a suspended nickel fine-particle catalyst at high activity under refluxing conditions.The isotope effects, kH/kD, for (CH3)2CDOH and (CD3)2CDOD were found to be 2.56 and 2.69, respectively, in contrast to 1.68 for (CH3)2CHOD, suggesting that the C-H bond dissociation at the methine position is rate-determining.With regard to (CH3)2CHOD and (CH3)2CDOH, a distinct difference was observed for the deuterium distributions among the liquid-phase components after the reaction, since deuterium transfer from the hydroxyl to the methyl and other groups proceeded tremendously for (CH3)2CHOD, whereas the methine group of (CH3)2CDOH changed little, even after a 5-h reaction under refluxing conditions.This contrast was well accounted for by the difficult splitting of the methine C-H bond and the facile dissociation of the hydroxyl group, in addition to a gradual H-D exchange due to the keto-enol equilibriation of the adsorbed acetone and the hydrogen transfer from 2-propanol to acetone.Distributions of H2, HD, and D2 were interpreted as well, which varied with the reaction periods and the kinds of substrates.Based on the proposed mechanism, strategies for a catalyst improvement suitable for a newly-proposed chemical heat pump system are discussed.
A New Method for Obtaining Isotopic Fractionation Data at Multiple Sites in Rapidly Exchanging Systems
Jarret, Ronald M.,Saunders, Martin
, p. 2648 - 2654 (2007/10/02)
A new method for rapidly and conveniently obtaining isotopic fractionation factors in dilute aqueous solutions of compounds containing rapidly exchanging OH, NH, and SH groups is described.Shifts in the positions of NMR peaks for spectroscopically observable nuclei induced by isotopic substitution are the basis of this procedure which has the unique capability of separately measuring the isotopic exchange constants simultaneously for several different groups in the same molecule.The results for a series of alcohols, amines, thiols, phenols, acids, and amides with use of 13C NMR spectroscopy are reported.Atypically low values of Kfrac are observed in several cases, indicating that there are strong internal hydrogen bonds in competition with those to water, yielding conformational information.
