活化硼氢化钠在有机合成中的应用

介绍了有机合成反应中NaBH4与添加剂共同作用的反应,其中包括烯烃和炔烃的还原,羧酸的还原,氨基酸及其衍生物的还原,羧酸酯的还原,酰胺的还原,腈基的还原,酰氯的还原,硝基化合物的还原,醛酮的还原等。与LiAIH4的还原相比较,其反应条件更温和,反应过程更安全、易操控、易放大。     

二碘化钐参与水相反应的研究现状

在水、胺以及四氢呋喃存在下二碘化钐参与的还原酮、亚胺以及α,β不饱舜口酯的反应能够在瞬间完成.这个速率要比在HMPA/醇催化体系要快100倍.这种新的还原体系被认为是取代有毒的六甲基磷酸三胺(HMPA)/醇催化还原体系的极好的方法.     

重氮还原法合成酮基布洛芬

以苯胺为原料,经酰化、环化、苯甲酰化,制得5-(苯甲酰基)-3-甲基苯-吲哚酮(2),化合物(2)在氢氧化钡溶液中开环、重氮化、次磷酸还原,一锅制得酮基布洛芬(1),总收率31.1%.     

表面活性剂介入酵母细胞催化芳香酮的对映选择性还原

以酵母细胞催化4'-氯苯乙酮合成(S)-1-4'-氯苯基乙醇为模型反应,研究了十六烷基三甲基溴化铵、十二烷基硫酸钠和壬基酚聚氧乙烯醚系列表面活性剂对酵母细胞催化4'-氯苯乙酮对映选择性还原反应的影响。结果表明,向反应体系中加入表面活性剂可明显提高4'-氯苯乙酮的转化率,而对产物(S)-1-4'-氯苯基乙醇对映体过量值的影响极小,壬基酚聚四氧乙烯醚(NP-4)是最合适的添加剂。此外,还考察了NP-4对酵母细胞催化系列芳香酮对映选择性还原反应的影响,结果表明,NP-4对产物(S)-1-芳基乙醇的对映体过量值几乎没影响,但对底物芳香酮转化率均有明显的提高,同时还发现底物转化率的提高幅度与芳香环上取代基的电子效应有关,取代基供电子能力越强越有利于底物转化率的增加。     

离子液体-水体系中二芳基甲醇合成研究

以离子液体—水体系为反应介质,硼氢化钾为还原剂,二芳基甲酮还原合成了二芳基甲醇。考察了不同离子液体对反应的影响及离子液体循环使用性能。还研究了不同取代基的二芳基甲酮的还原反应过程。反应在室温下进行、时间短、收率高、后处理简单,且疏水性离子液体可以方便地回收和多次循环使用,对反应的效果无明显降低,对环境友好。     

1-（2，4-二氯苯基）-2-（1-咪唑基）乙醇的合成工艺改进

2,4,ω-三氯苯乙酮与咪唑进行N-烷基化反应制得a-（1-眯唑基）-2．4-二氯苯乙酮（2）：2经硼氢化钾还原得1-（2,4-二氯苯基）-2-咪乙醇。     

(R,S)-(1-羟基-2-异丙氨基)甲磺酰苯胺盐酸盐的合成及工艺改进

以对销基苯乙酮为原料经还原反应，甲磺化反应，溴代反应，与异丙胺的亲核取代和酮氢化钠还原，异丙醇精制而得经工艺改进，各部收率均有较大的提高，总收率达36．02％。     

全反式替普瑞酮的化学全合成研究

以香叶醇和乙酸香叶酯为原料,香叶醇经溴化和亚磺酰化两步反应合成香叶基砜（3）,乙酸香叶酯经氧化、还原和溴化3步反应合成中间体6,化合物3和6偶联的产物在锂胺溶液中脱除砜基得到香叶基香叶醇（8）,化合物8经溴化、烷基化和脱羧3步反应合成全反式替普瑞酮（10）。     

3,5-二羟基戊苯的新合成方法研究

以3,5-二羟基苯甲酸为起始原料,经苯甲酰化羟基后,用二氯亚砜氯代得到酰氯衍生物。酰氯与有机锌试剂C4H9Zn Br反应生成相应的酮,酮经水合肼还原生成3,5-二苯甲酸酯基戊苯,水解脱保护得产物3,5-二羟基烷基苯。     

糖醇在食品中的作用

糖醇是由碳、氢、氧三元素组成的化合物,按其结构可分为单糖醇(如赤藓糖醇、木糖醇、山梨糖醇、甘露糖醇)、双糖醇(如麦芽糖醇、乳糖醇、异麦芽酮糖醇)。糖醇是糖的醛基、酮基或半缩醛羟基(还原性双糖)被还原为羟基所形成的多元醇化合物。     

基于机器学习的二氧化碳电化学还原制备甲酸盐研究

系统研究了不同双金属中心催化剂催化二氧化碳电化学还原制备甲酸盐。借助机器学习,确定了反应中心金属原子序数、电负性和电离能等特征对双金属中心催化剂表面二氧化碳还原具有主要的影响。基于这些特征,通过高通量机器学习快速预测了105种双金属中心催化剂二氧化碳电还原制甲酸盐及其主要竞争反应的Gibbs自由能变,筛选出29种双金属中心催化剂更倾向于二氧化碳还原得到甲酸盐,是潜在的转化二氧化碳为甲酸盐的高性能催化材料。运用类似的方法预测了105种双金属中心催化剂表面二氧化碳还原中间体的结构,发现中间体吸附能与其吸附构型具有显著的相关关系。     

Chemical transformations of poly(arylene ether ketones) containing side functional groups

Conditions for chemical transformations of poly(arylene ether ketones) containing side carboxyl and phthalimidine functional groups have been investigated. The reason why the chemical modification of poly(arylene ether ketones) with side acid chloride groups leads in some cases to the formation of insoluble products is established. Ionogenic and comb-shaped poly(arylene ether ketones) with hydrophobic fragments in side branches are obtained through chemical transformations of previously synthesized polymers containing side carboxyl, hydroxyl (alcohol), and phthalimidine groups. The properties of poly(arylene ether ketones) can be varied in a wide range via chemical reactions of side reactive groups.     

Application of Tethered Ruthenium Catalysts to Asymmetric Hydrogenation of Ketones,and the Selective Hydrogenation of Aldehydes

An improved method for the synthesis of tethered ruthenium(II) complexes of monosulfonylated diamines is described, together with their application to the hydrogenation of ketones and aldehydes. The complexes were applied directly, in their chloride form, to asymmetric ketone hydrogenation, to give products in excess of 99% ee in the best cases, using 30 bar of hydrogen at 60 °C, and to the selective reduction of aldehydes over other functional groups.     

Amino acid derived amides and hydroxamic acids as ligands for asymmetric transfer hydrogenation in aqueous media

Amides and hydroxamic acids derived from α-amino acids were evaluated as ligands in combination with rhodium and iridium half-sandwich complexes in asymmetric transfer hydrogenation (ATH) of ketones. The reactions were performed in aqueous media using lithium formate as hydride source. The catalyst systems turned out to be highly efficient and ee's up to 90% were obtained.     

Low temperature water gas shift: Type and loading of metal impacts forward decomposition of pseudo-stabilized formate over metal/ceria catalysts

A similar degree of surface shell reduction of ceria was obtained for a series of metal/ceria catalysts. Surface formate species were generated by reaction of CO with bridging OH groups associated with the Ce³⁺ defects. Forward decomposition of the pseudo-stable formates was followed in flowing H₂O, leading to the production of surface carbonate species. The forward formate decomposition rate was enhanced changing the promoter from Au to Pt, and by increasing the promoter loading (from 0.5 to 2.5%). Results suggest that formate CH bond breaking is not only facilitated by H₂O, but it is further enhanced by type and loading of metal promoter. From earlier kinetic isotope effect and isotopic tracer studies, the rate-limiting step of the forward formate decomposition (WGS reaction) was considered to be associated with CH bond rupture of the formate. The results can explain the promotion in the WGS rates observed for these samples by changing from Au to Pt and by increasing the promoter loading.     

Reduction of Carbonyl to Methylene: Organosilane-Ga(OTf)<Subscript>3</Subscript> as an Efficient Reductant System

Abstract  

Direct carbonyl reduction to methylene has been achieved by mild reductant system obtained from the combination of organosilane and gallium (III) trifluoromethanesulfonate {Ga(OTf)₃}, a water tolerant, recyclable, catalyst. Among a series of organosilanes studied, dimethylchlorosilane (Me₂SiHCl, DMCS) showed the highest efficiency. Both aromatic and aliphatic ketones were effectively reduced to the corresponding methylene products with high functional groups tolerance, under very mild conditions in a relatively short period of time with good to excellent yields.     

Volatile products from mild oxidation of methyl linoleate. Analysis by combined mass spectrometry-gas chromatography

The volatile products from autoxidation of methyl linoleate have been analyzed by combined mass spectrometry-gas chromatography. The principal components were pentanal, hexanal, amyl formate, methyl octanoate, and substituted dioxolanes. Minor components included esters, alcohols, ketones, aldehydes, hydrocarbons, and acetals. Certain unsaturated carbonyl compounds, previously reported, were not detected. A laboratory of the W. Utiliz. Res. Devel. Div., ARS, USDA.     

Low temperature water–gas shift: Differences in oxidation states observed with partially reduced Pt/MnOX and Pt/CeOX catalysts yield differences in OH group reactivity

The Pt–ceria synergy may be described as the dehydrogenation of formate formed on the surface of the partially reducible oxide (PRO), ceria, by Pt across the interface, with H₂O participating in the transition state. However, due to the rising costs of rare earth oxides like ceria, replacement by a less expensive partially reducible oxide, like manganese oxide, is desirable. In this contribution, a comparison between Pt/ceria and Pt/manganese oxide catalysts possessing comparable Pt dispersions reveals that there are significant differences and certain similarities in the nature of the two Pt/PRO catalysts. With ceria, partial reduction involves reduction of the oxide surface shell, with Ce³⁺ at the surface and Ce⁴⁺ in the bulk. In the case of manganese oxide, partial reduction results in a mixture of Mn³⁺ and Mn²⁺, with Mn²⁺ located at the surface. With Pt/CeO_X, a high density of defect-associated bridging OH groups react with CO to yield a high density of the formate intermediate. With Pt/MnO_X, the fraction of reactive OH groups is low and much lower formate band intensities result upon CO adsorption; moreover, there is a greater fraction of OH groups that are essentially unreactive. Thus, much lower CO conversion rates are observed with Pt/MnO_X during low temperature water–gas shift. As with ceria, increasing the Pt loading facilitates partial reduction of MnO_X to lower temperature, indicating metal–oxide interactions should be taken into account.     

The use of sodium formate for the recovery of precious metals from acidic base metal effluents

Zinc was used for the reduction of the platinum group metals (PGMs) in acidic effluents. Due to the increasing cost of zinc, sodium formate was investigated as an alternative reductant. In a base metal‐containing acidic effluent, called diethylenetriamine barren, sodium formate was used to precipitate the PGMs. This effluent was the filtrate obtained after a precipitation procedure had been used to remove rhodium and iridium. It was found that pH 1.5 was the optimum starting pH for sodium formate reduction. The pH increased to approximately 4.5 after the addition of sodium formate. The optimum concentration of sodium formate was found to be 30 g dm^?3 at a temperature of 100 °C where the process time was 6 h. Platinum and palladium were the most effectively reduced PGMs, both exhibiting an average precipitation efficiency of greater than 99%. Difficulty was experienced with the precipitation of iridium (average precipitation efficiency of 76%). The precipitated PGMs readily dissolved in hydrochloric acid (6 M ) and sodium chlorate (2%). A reduction in costs resulted from the discontinuation of the use of zinc for reduction purposes. An additional advantage was that zinc was no longer introduced into the PGM refinery circuits. © 2001 Society of Chemical Industry     

酮类化合物的不对称还原

近年来选择性还原在有机化学领域中越来越引起众多学者的关注,由酮类化合物不对称还原为醇类化合物成为有机合成化学的前沿领域,发展迅速,并取得了许多成就。本文综述了近几十年来酮类化合物的不对称还原研究进展,对各种不对称还原反应进行了分别介绍。