Mechanism of prooxidant reaction of vitamin E: kinetic, spectroscopic, and ab initio study of proton-transfer reaction
摘要:
To shed light on the mechanism of proton-transfer reactions, a kinetic, spectroscopic, and ab initio study of the prooxidant action of vitamin E derivatives has been carried out. The second-order rate constants (k(-s)'s) for the reaction of six tocopheroxyl radicals (Toc.'s) with five alkyl hydroperoxides (ROOHs) in benzene were determined spectrophotometrically. The first adiabatic ionization potentials (I(a)'s) of ROOHs were obtained by means of photoelectron spectroscopy. The result indicates that k(-s) increases as the electron-donating capacity of the alkyl substituents of ROOH increases and I(a) decreases. The methylation at the aromatic ring of Toc. reduces the k(-s) for a given ROOH. k(-s) for the reaction of deuterated alkyl hydroperoxides (ROODs) with a Toc. in a mixed solution of benzene and ethanol-d1 was also measured. A deuterium kinetic isotope effect on k(-s) is observed. For a given Toc., plots of log k(-s) vs I(a) for various ROOHs and log k(-s) vs Tafts sigma* constant of alkyl substituents of ROOH are found to be linear. The slope of the plot of log k(-s) vs sigma* for ROOD is similar to that for ROOH. The geometries of ROOHs were optimized, and the Koopmans' theorem first ionization potentials (I(K)'s) for those geometries were calculated with the ab initio method. A plot of log k(-s)the reactions of a Toc. with various ROOHs vs I(K) of the ROOH is also found to be linear. From these results, it is considered that both charge transfer and proton tunneling play important roles in the prooxidant reaction of TocH. The transition state in the prooxidant reaction has properties of the charge-transfer species. The proton tunneling takes place below the transition state. Tunneling allows the proton to cut a corner on the potential energy surface. Our explanation will be widely applicable to many transfer reactions.
A new binuclear oxovanadium(v) complex as a catalyst in combination with pyrazinecarboxylic acid (PCA) for efficient alkane oxygenation by H2O2
作者:Manas Sutradhar、Nikita V. Shvydkiy、M. Fátima C. Guedes da Silva、Marina V. Kirillova、Yuriy N. Kozlov、Armando J. L. Pombeiro、Georgiy B. Shul'pin
DOI:10.1039/c3dt50584g
日期:——
[VO(OEt)(EtOH)}2L] (1) where H4L is bis(2-hydroxybenzylidene)terephthalohydrazide has been synthesized and fully characterized. The combination of 1 with pyrazine-2-carboxylic acid (PCA; a cocatalyst) affords a catalytic system for the efficient oxidation of saturated hydrocarbons, RH, with hydrogen peroxide and air in acetonitrile solution at 50 °C to produce alkylhydroperoxides, ROOH, as the main
Branching Ratios for the Reaction of Selected Carbonyl-Containing Peroxy Radicals with Hydroperoxy Radicals
作者:Alam S. Hasson、Geoffrey S. Tyndall、John J. Orlando、Sukhdeep Singh、Samuel Q. Hernandez、Sean Campbell、Yesenia Ibarra
DOI:10.1021/jp211799c
日期:2012.6.21
important chemical sink for organic peroxy radicals (RO2) in the troposphere is reaction with hydroperoxy radicals (HO2). Although this reaction is typically assumed to form hydroperoxides as the major products (R1a), acetyl peroxy radicals and acetonyl peroxy radicals have been shown to undergo other reactions (R1b) and (R1c) with substantial branchingratios: RO2 + HO2 → ROOH + O2 (R1a), RO2 + HO2 →
对流层中有机过氧自由基(RO 2)的重要化学吸收剂是与氢过氧自由基(HO 2)的反应。尽管通常假定该反应会形成氢过氧化物作为主要产物(R1a),但已证明乙酰基过氧自由基和丙酮基过氧自由基会进行其他反应(R1b)和(R1c),并具有明显的支化比:RO 2 + HO 2 →ROOH + O 2(R1a),RO 2 + HO 2 →ROH + O 3(R1b),RO 2 + HO 2 →RO + OH + O 2(R1c)。理论工作表明,反应(R1b)和(R1c)可能是酰基过氧和α-羰基过氧自由基的一般特征。在这项工作中,得出了六个含羰基的过氧自由基的R1a–R1c的支化比:C 2 H 5 C(O)O 2,C 3 H 7 C(O)O 2,CH 3 C(O)CH 2 O 2,CH 3 C(O)CH(O 2)CH 3,CH 2 ClCH(O 2)C(O)CH 3和CH 2 ClC(CH 3)(O 2
Oxidations by the system “hydrogen peroxide - manganese(IV) complex - acetic acid” — Part II. Hydroperoxidation and hydroxylation of alkanes in acetonitrile
作者:Georgiy B Shul'pin、Georg Süss-Fink、John R Lindsay Smith
DOI:10.1016/s0040-4020(99)00233-1
日期:1999.4
ethane, propane, normalbutane and isobutane) can be also easily oxidized by the same reagent in acetonitrile solution, the conditions being very mild: low pressure (1–7 bar of the alkane) and low temperature (−22 to +27 °C). Catalyst turnover numbers attain 3100, the yield of oxygenated products is 22% based on the alkane. The yields of oxygenates are higher at low temperatures. The ratio of products
高级烷烃(环己烷,正戊烷,正庚烷,甲基丁烷,2-和3-甲基戊烷,3-甲基己烷,顺式和反式十氢化萘)在20°C下在空气中于乙腈中被H 2 O 2氧化(或(IV)锰盐[L 2 Mn 2 O 3 ](PF 6)2存在下(L = 1,4,7-三甲基-1,4-7-三氮杂环壬烷)作为催化剂。反应混合物的必需组分是乙酸。2小时后的营业额达到3300,基于烷烃的氧化产物收率为46%。氧化最初提供相应的烷基氢过氧化物作为主要产物,但是随后这些化合物分解产生相应的酮和醇。反应的区域和键选择性很高:C(1):C(2):C(3):C(4)≈1:40:35:35和1°:2°:3°是1: (15–40):(180–300)。与十氢化萘的两种异构体反应,得到(用PPh 3处理后)在叔位羟基化的醇,如果是顺式,则顺式/反式比为〜2-十氢化萘,如果是反式十氢化萘,则约为30 (即在后者的情况下,反应是立体特异性的)。轻链烷
Hydrogen Peroxide Oxygenation of Alkanes Including Methane and Ethane Catalyzed by Iron Complexes in Acetonitrile
作者:Georgiy B. Shul'pin、Galina V. Nizova、Yuriy N. Kozlov、Laura Gonzalez Cuervo、Georg Süss-Fink
DOI:10.1002/adsc.200303147
日期:2004.2
This paper describes an investigation of the alkane oxidation with hydrogen peroxide in acetonitrile catalyzed by iron(III) perchlorate (1), iron(III) chloride (2), iron(III) acetate (3) and a binuclear iron(III) complex with 1,4,7-triazacyclononane (4). The corresponding alkyl hydroperoxides are the main products. Nevertheless in the kinetic study of cyclohexane oxidation, the concentrations of oxygenates
Syntheses, Structures, and Reactivities of Cobalt(III)−Alkylperoxo Complexes and Their Role in Stoichiometric and Catalytic Oxidation of Hydrocarbons
作者:Ferman A. Chavez、John M. Rowland、Marilyn M. Olmstead、Pradip K. Mascharak
DOI:10.1021/ja9814873
日期:1998.9.1
Although Co(III)−alkyl peroxo species have often been implicated as intermediates in industrial oxidation of hydrocarbons with cobalt catalysts, examples of discrete [LCoIII−OOR] complexes and studies on their oxidizing capacities have been scarce. In this work, twelve such complexes with two different ligands, L, and various primary, secondary, and tertiary R groups have been synthesized, and seven