烯烃的选择性电化学氧化:研究进展与前景（英文）

烯烃类化合物,如乙烯和丙烯,是工业生产的关键原料,它们可以通过选择性氧化转化为环氧乙烷(EO)和环氧丙烷(PO)等高附加值的化学品.目前,烯烃类化合物转化主要通过热化学途径实现,通常需要高温高压条件,并可能导致过度氧化生成CO₂,因而选择性较低,且对经济和环境效益不友好.与此相对,电催化反应以电能作为驱动力,通过优化催化剂、电解液和反应电位等,有望在相对温和的条件下提高反应的选择性和能量效率,为高选择性烯烃氧化提供一种潜在策略.然而,当前烯烃的电化学选择性氧化的电流密度较低,整体生产成本相对较高,因此,有必要进一步研发高效且稳定的电化学选择性氧化烯烃的体系.本文综述了近期关于烯烃选择性电化学氧化的研究进展,研究主要集中在两个方面:一是烯烃在电极和电解液界面上直接进行电化学氧化的方法;二是通过电化学反应原位生成氧化剂(如Cl₂和H₂O₂)后,再对烯烃进行氧化的间接方法.对于烯烃的直接电化学氧化,反应的选择性可以通过调控几何效应和电子效应来优化.具体来说,通过引入如氯离子这样的物种,减少催化剂表面的可用...     

甲苯选择性氧化制苯甲醛：铁锑氧化物表面性质与催化性能的研究

甲苯选择性氧化制苯甲醛——铁锑氧化物表面性质与催化性能的研究葛欣张惠良（南京大学化学系南京２１００９３）关键词铁锑氧化苯甲醚甲苯选择性氧化中图分类号Ｏ６４３．３２２铁锑氧化物是烯烃氧化反应中催化剂的主要组成之一［１］，在催化剂中当Ｓｂ／Ｆｅ从１．０变...     

有机锂试剂和含氟β-酮基磷盐的反应-一种合成含氟烯烃的新方法

本文报道一种合成含氟烯烃的新方法,有机锂试剂进攻含氟β-酮基磷盐, 亲核反应发生在邻接于全氟烷基的羰基碳原子上,接着消去三苯基氧膦,同时生成四取代含氟烯烃.反应是"一锅"法进行的,多步反应产率在42～70%之间.反应的应用范围较广,取代基可以是烷基,烯丙基,苄基和脂环基,本文还讨论了反应的立体化学结果     

锇催化烯烃双羟基化的反应原理与立体选择性

介绍了四氧化锇催化不对称烯烃双羟基化的反应原理和以N-甲基吗啉-N-氧化物(N-methylmorpholine-N-oxide,NMO)、铁氰化钾K3[Fe(CN)6]为氧化剂时烯烃双羟基化反应的催化循环;此外,还介绍了该催化反应立体选择性的机理和一些研究进展以及催化体系中手性配体的选择。     

碱土金属氧化物担载Fe—MnO催化剂的CO加氢反应制低碳烯烃性能

碱土金属氧化物担载Ｆｅ－ＭｎＯ催化剂可大幅度提高低碳烯烃的选择性和ＣＯ转化率，添加碱金属助剂将进一步改善其催化性能；ＭｎＯ是铁催化剂由合成气制烯烃的有效助剂；碱土金属氧化物担体能抑制乙烯发生歧化反应及丙烯加氢反应，而ＭｎＯ助剂主要抑制乙烯加氢反应，从而有利于提高合成气制低碳烯烃的选择性。     

羰基化合物及其与卤代烃在CeCl_3/萘锂试剂作用下的反应

用萘锂(LiNp)还原无水CeCl_3制得的活性金属铈(Ce~*)在与羰基化合物的反应中,与用相同方法制得的Nd~*相比,表现出更高的反应活性。Ce~*与羰基化合物反应经水解可生成相应的醇,频哪醇和烯烃,其选择性不仅与反应时间和温度有关,而且还与羰基化合物的种类以及CeCl_3:LiNp:RCOR＇的摩尔比有关。初步研究了Ce~*作用下的酮和一些卤代烃的反应。     

铑催化的烯烃不对称氢甲酰化反应研究进展

烯烃的氢甲酰化反应是工业上最重要的均相催化反应之一,而通过烯烃的不对称氢甲酰化反应合成光学活性醛,对于药物、农药、香料和天然产物合成方面具有重要的意义.近年来,由于铑与膦配体形成的络合物在催化烯烃的不对称氢甲酰化反应中具有反应活性高、选择性好等优点而引起广泛关注.通过调控铑络合物中手性膦配体的电子与立体化学环境,已经成为实现不对称氢甲酰化反应高活性和高选择性最主要的方法.主要介绍了近期在铑催化的不对称氢甲酰化反应研究方面取得的进展,重点介绍几类代表性的手性膦配体在此类反应中的应用.     

镧系金属用于有机反应的研究—NdCl3／萘锂体系与羰基化合物…

由萘锂还原无水ＮｄＣｌ３制得的活性金属Ｎｄ＾＃在与羰基化合物的反应中显示出较高的反应活性。该反应经水解可生成相应的醇、片呐醇和烯烃，其还原状态不仅与羰基化合物的性质有关，还取决于Ｎｄ＾＃：ＲＣＯＲ＇的摩尔比以及反应温度和反应时间。本文还较详细地研究了Ｎｄ＾＃：二苯酮的反应，不同的Ｎｄ＾＃：二苯酮摩尔比以及外加配体或改变溶剂都将改变该反应的选择性。对该反应的机理亦进行了探讨。     

镧系金属用于有机反应的研究──NdCl_3／萘锂体系与羰基化合物的反应

由萘锂还原无水ＮｄＣｌ_３制得的活性金属Ｎｄ＊在与羰基化合物的反应中显示出较高的反应活性。该反应经水解可生成相应的醇、片呐醇和烯烃，其还原状态不仅与羰基化合物的性质有关，还取决于Ｎｄ＊：ＲＣＯＲ′的摩尔比以及反应温度和反应时间。本文还较详细地研究了Ｎｄ＊：二苯酮的反应，不同的Ｎｄ＊：二苯酮摩尔比以及外加配体或改变溶剂都将改变该反应的选择性。对该反应的机理亦进行了探讨。     

氟烷基化和氟烷氧基化的研究19: 铱(I)催化下氟烷基碘与烯烃、炔烃的加成反应

在羰基-三(三苯基膦)氢化铱(I)催化下, 氟烷基碘与烯烃加成得到高产率的加成产物, 反应条件温和, 有良好的选择性. 氟烷基碘也可与炔烃反应, 生成以E式异构体占优势的氟烷基化烯烃. 反应体系中加入自由基抑制剂或单电子转移阻止剂则大大减慢反应; 二烯丙基醚可以捕获自由基生成四氢呋喃衍生物; 光电子能谱表明部分一价铱在反应后价态升高, 这些事实表明反应为单电子转移引发下的自由基链式机理.     

Kinetics and thermodynamics of limonene ozonolysis

Using density functional methods, the initial reaction steps of limonene ozonolysis have been investigated with a focus on primary ozonide formation and its decomposition to Criegee intermediates and carbonyl compounds. The ozonide formation is highly exothermic, and the decomposition channels have similar free energies of activation, ΔG(?), indicating that there is no primary pathway for ozonide decomposition. Assuming that ozonide formation is the rate limiting step, the theoretical rate coefficient, k = 1.6 × 10(-16) molecule(-1) cm(3) s(-1), evaluated at the CCSD(T)/6-31G(d,p)//BHandHLYP/cc-pvdz level and 298.15 K for d-limonene is in good agreement with the experimental value, k(exp) = 3.3 × 10(-16) molecule(-1) cm(3) s(-1). The theoretical Arrhenius expression is also in good agreement with experimental results.     

Complete ozonolysis of alkyl substituted ethenes at -60 degrees C: distributions of ozonide and oligomeric products

The distribution of ozonide and oligomeric structures formed on complete ozonolysis of alkenes in a non-participating solvent at -60 degrees C is governed by the alkyl substitution around the carbon-carbon double bond. The ozonolysis of a 1,1-alkyl substituted ethene generally favours the formation of an ozonide (a 1,2,4-trioxolane). Whereas the ozonolysis of a 1,1,2-alkyl substituted ethene also produces ozonide, a considerable amount of the ozonised products are oligomeric in nature. For example, the ozonolysis of 3-methylpent-2-ene in solution to high conversion in pentane yields oligomers with structural units derived from the fragmentation products of the primary ozonide (a 1,2,3-trioxolane) which are namely butanone carbonyl oxide and acetaldehyde; these can be characterised by electrospray ionisation mass spectroscopy (ESI-MS) under soft ionisation conditions. The predominant oligomers formed are rich in carbonyl oxide units (80 + mol%) and are cyclic in nature. A small proportion of the oligomers formed are open chain compounds with end groups that suggest that chain termination is brought about either by water or by hydrogen peroxide. Residual water in the solvent will react with the carbonyl oxides to produce 2-methoxybut-2-yl hydroperoxide, which we propose readily decomposes generating hydrogen peroxide. A significant yield of oligomers also is obtained from the ozonolysis of a 1,2-alkyl substituted ethene. The ozonolysis of trans-hex-2-ene in pentane yields oligomers containing up to four structural units and are predicted to be mainly cyclic.     

Direct measurement of Criegee intermediate (CH2OO) reactions with acetone, acetaldehyde, and hexafluoroacetone

Criegee biradicals, i.e., carbonyl oxides, are critical intermediates in ozonolysis and have been implicated in autoignition chemistry and other hydrocarbon oxidation systems, but until recently the direct measurement of their gas-phase kinetics has not been feasible. Indirect determinations of Criegee intermediate kinetics often rely on the introduction of a scavenger molecule into an ozonolysis system and analysis of the effects of the scavenger on yields of products associated with Criegee intermediate reactions. Carbonyl species, in particular hexafluoroacetone (CF(3)COCF(3)), have often been used as scavengers. In this work, the reactions of the simplest Criegee intermediate, CH(2)OO (formaldehyde oxide), with three carbonyl species have been measured by laser photolysis/tunable synchrotron photoionization mass spectrometry. Diiodomethane photolysis produces CH(2)I radicals, which react with O(2) to yield CH(2)OO + I. The formaldehyde oxide is reacted with a large excess of a carbonyl reactant and both the disappearance of CH(2)OO and the formation of reaction products are monitored. The rate coefficient for CH(2)OO + hexafluoroacetone is k(1) = (3.0 ± 0.3) × 10(-11) cm(3) molecule(-1) s(-1), supporting the use of hexafluoroacetone as a Criegee-intermediate scavenger. The reactions with acetaldehyde, k(2) = (9.5 ± 0.7) × 10(-13) cm(3) molecule(-1) s(-1), and with acetone, k(3) = (2.3 ± 0.3) × 10(-13) cm(3) molecule(-1) s(-1), are substantially slower. Secondary ozonides and products of ozonide isomerization are observed from the reactions of CH(2)OO with acetone and hexafluoroacetone. Their photoionization spectra are interpreted with the aid of quantum-chemical and Franck-Condon-factor calculations. No secondary ozonide was observable in the reaction of CH(2)OO with acetaldehyde, but acetic acid was identified as a product under the conditions used (4 Torr and 293 K).     

Effects of the substituents on the reactivity of carbonyl oxides. A theoretical study on the reaction of substituted carbonyl oxides with water

The reactions between fifteen carbonyl oxides and water have been investigated with the aim of contributing to a better understanding of the effects of the substituents in the reactivity of carbonyl oxides. We have employed density functional theory and large scale ab initio methods (CCSD(T), CASSCF, and CASPT2), combined with transition state theory, to investigate the addition of water to carbonyl oxide and, for those carbonyl oxides having a methyl substituent in syn, the hydrogen transfer from the methyl group to the terminal oxygen of carbonyl oxide. In this case, the water acts as a catalyst and this reaction can contribute to the atmospheric formation of a hydroxyl radical. Carbonyl oxides with electron withdrawing substituents and zwitterionic character have low energy barriers and react fast, whereas carbonyl oxides with electron releasing substituents have high energy barriers and react slowly. The position of the substituents plays also an important role and carbonyl oxides having a hydrogen atom substituent in syn react faster than carbonyl oxides having a hydrogen atom substituent in anti. The differences in the reactivity of different substituted carbonyl oxides raise up to ten orders of magnitude and the branching ratios for the two different reactions investigated are also reported.     

First Exclusive Regioselective Fragmentation of Primary Ozonides Controlled by Remote Carbonyl Groups and a New Method for Determining the Regiochemistry of Carbonyl Oxide Formation

The first exclusive regioselective fragmentation of primary ozonides controlled by remote carbonyl groups on ozonolysis of norbornene derivatives and reaction of final ozonides with triethylamine as a new probe for determining the regiochemistry of carbonyl oxide formation from primary ozonide fragmentation are reported. Ozonolysis of the endo adducts 3a-d and the deuterated compounds 8a and 8b in CDCl(3) at -78 degrees C gave the final ozonides 4a-d, 9a, and 9b as the sole products (>95%), respectively. No detectable amount of the isomeric final ozonides 5, 10, 11, and 12 was obtained. A mechanism is proposed to account for the exclusive regioselective fragmentation of the primary ozonides. Ozonolysis of 3a-d, 8a, and 8b in CH(2)Cl(2) at -78 degrees C followed by treatment with triethylamine exclusively gave the convex tetraquinane oxa cage compounds 16a-d, 19a, and 19b in 85-90% yields, respectively. No detectable amount of the other regioisomers 17a-d, 20a, and 20b was obtained. Ozonolysis of 3a-d, 8a, and 8b in CH(2)Cl(2) at -78 degrees C followed by reduction with dimethyl sulfide gave the tetraacetal tetraoxa cage compounds 21a-d, 23a, and 23b in 85% yields, respectively. The difference in function between triethylamine and dimethyl sulfide in reaction with final ozonide is demonstrated. Ozonolysis of the endo adducts 24a and 24b in CDCl(3) at -78 degrees C exclusively gave the final ozonides 27a and 27b, respectively. The order of the preference of various remote carbonyl groups to control the fragmentation of the primary ozonides formed by ozonolysis of norbornene derivatives is investigated. Ozonolysis of the endo esters 32a-c in CH(2)Cl(2) at -78 degrees C followed by reduction with dimethyl sulfide gave the new tetraacetal oxa cages 35a-c, with an alkoxyl group directly on the skeleton, and the novel triacetal oxa cages 36b and 36c, respectively. The structures of triacetal oxa cages are proven for the first time by X-ray analysis of the crystalline compound 36c.     

Direct observation of the gas-phase Criegee intermediate (CH2OO)

Carbonyl oxide species play a key role in tropospheric oxidation of organic molecules and in low-temperature combustion processes. In the late 1940s, Criegee first postulated the participation of carbonyl oxides, now often called "Criegee intermediates," in ozonolysis of alkenes. However, despite decades of effort, no gas phase Criegee intermediate has before been observed. As a result, knowledge of gas phase carbonyl oxide reactions has heretofore been inferred by indirect means, with derived rate coefficients spanning orders of magnitude. We have directly detected the primary Criegee intermediate, formaldehyde oxide (CH2OO), in the chlorine-initiated gas-phase oxidation of dimethyl sulfoxide (DMSO). This work not only establishes that the Criegee intermediate is formed in DMSO oxidation also but opens the possibility for explicit kinetics studies on this critical atmospheric species.     

Solvent effects on ozonolysis reaction intermediates

Solvent effects on relative stability, electronic and molecular structure of ozonolysis reaction intermediates are analyzed with the help of ab initio MP2/6-31+G^** calculations. A continuum model is employed to account for solute–solvent electrostatic interactions. The results show that there are large effects on the structure and relative stability of carbonyl oxide by substantially favoring its zwitterionic character. A complex formed by carbonyl oxide and formaldehyde is shown to be stable in the gas phase and in solution. This complex can be involved in solvent cage reactions leading to secondary ozonides. Thermodynamically, primary ozonide decomposition is favored by the solvent.     

An Efficient Method for Preparing the α-Deuterated-α,β-Unsaturated Carbonyl Compounds by Reaction of Stable Phosphonium Ylides with Carbonyl Compounds in Deuterium Oxide

Carbonyl compounds reacted with stable phosphonium ylides in D₂O to give α-deuterated-α,β-unsaturated carbonyl compounds in the same flask. The chemical yield and deuterium incorporation are excellent under our procedure. The fragile group like ozonide was compatible with our reaction condition.     

A theoretical study of the reactions of carbonyl oxide with water in atmosphere: the role of water dimer

Carbonyl oxide is a well-known intermediate formed in gas-phase reactions of ozone with alkenes. Secondary reactions of carbonyl oxide are suggested to lead to the formation of HO, H₂O₂ and organic peroxides in the atmosphere. We performed a theoretical study of reactions of carbonyl oxide with water and a water dimer. Using CCSD(T)/6-311+G(2d,2p)//B3LYP/6-311+G(2d,2p) calculations we found that the most energetically favourable channel is the formation of hydroxymethyl hydroperoxide (HMHP) as the result of reactions of carbonyl oxide with the water dimer. The potential importance of water dimer reactions in the chemistry of the troposphere is discussed herein.     

Silylketenes under Kulinkovich conditions: alkene/ketene exchange versus nucleophilic addition. Application to the stereoselective preparation of vinylcyclopropanols

Silylketenes react under Kulinkovich conditions through two competitive pathways: alkene/ketene exchange versus nucleophilic addition. In both cases, the organotitanium intermediate reacts with an aldehyde to yield an adduct which can undergo an elimination to yield a vinylcyclopropanol or an α,β-unsaturated carbonyl compound.