超(近)临界水中的有机合成反应

作为一种环境友好的化学工艺过程,以超(近)临界水作有机合成反应介质越来越受到人们的关注。人们考察了在超(近)临界水中的许多有机反应,并获得了预期的结果。综述了近年来超(近)临界水中的有机合成反应的研究进展。     

临界溶剂化作用对水解反应动力学的影响

用过渡态及Kirkwood介电模型考察近临界水中醋酸甲酯(MeAc)水解动力学.实验结果表明,临界溶剂化作用使本体系在623K附近出现反应活化体积(ΔV^≠)极负值现象,同时反应表观活化能降低至(23.5±8.29)kJ/mol.利用lnkc与反应场的线性关系可修正压力因素对水解动力学的影响,并证实了近临界水介质中MeAc水解S_N2反应机理的可靠性.     

超(近)临界水在有机化学反应中的应用

处于临界点及其附近的水可以作为环境友好的溶剂和催化剂应用于化学反应.本文概述了近年来超(近)临界水在重要有机化学反应中的应用.     

在氟溶剂中的绿色酯化反应

以全氟壬烯为氟溶剂, 对物质的量的羧酸和醇的酯化反应进行了系统研究. 在不移走生成物的条件下, 酯与全氟壬烯能形成氟两相体系而脱离酯化可逆反应体系, 促进反应平衡右移, 使收率提高10%～47%, 氟溶剂通过冷却和简单的相分离, 就可回收并直接套用. 氟溶剂在有机相中的损失小. 在氟溶剂中的酯化反应回流温度有较大幅度的下降.     

4-(2-(4′-吡啶)乙炔)苯基重氮盐的光化学反应动力学及其自组装单分子膜的表征

以4-(2-(4′-吡啶)乙炔)苯基芳香重氮盐为研究对象,在紫外光(250W,245nm)照射下,利用紫外-可见吸收光谱对该芳香重氮盐的乙腈溶液以及自组装单分子膜室温光解反应动力学进行了研究,确定了两种状态下的光解过程都符合一级反应动力学规律,并且溶剂极性使该重氮盐更容易发生光解反应.通过X射线光电子能谱(XPS)和电化学表征证实了4-(2-(4′-吡啶)乙炔)苯基芳香重氮盐经光解反应实现对石英片和氧化铟锡导电玻璃(ITO)表面的组装修饰,得到了通过共价键与基底联结的4-(2-(4′-吡啶)乙炔)苯自组装单分子膜,从而为其后基于有机-金属层层自组装技术构筑新型功能超薄膜奠定了基础.     

超(近)临界水中的化学反应

水作为自然界最常用的绿色介质在化学反应中已经得到广泛应用.近年来,随 着超临界技术的发展,人们对超(近)临界水的认识逐渐深入,以超(近)临界水为介质进 行化学反应的研究引起了人们的极大兴趣,开展了许多卓有成效的工作.本文在介绍超(近)临界水性质的基础上,主要对近年来超(近)临界水中的有机合成、无机化学反应、生物质的转化反应及聚合物的降解等方面的研究进展进行了回顾总结.     

双金属氰化络合物催化环氧丙烷和邻苯二甲酸酐共聚

采用双金属氰化络合物 (DMC)催化环氧丙烷 (PO)和邻苯二甲酸酐 (PA)共聚 ,探讨了共聚合特征 ,并用IR、1 H NMR和GPC对共聚物的结构和分子量进行了表征 .发现DMC催化剂对该共聚反应速度快 ,转化率高 ,是该反应的有效催化剂 ,催化剂浓度为 6 0mg kg时 ,90℃下 ,以THF作溶剂共聚反应 3h ,转化率可达94 0 % .聚合速度甚至比DMC催化PO均聚还快 .该共聚反应可在多种溶剂中进行 ,极性溶剂更有利于共聚合 ,溶液聚合温度比本体共聚低 ,合适的溶液共聚温度在 90～ 10 0℃之间 .共聚产物的分子量受催化剂用量、反应温度和体系中水份含量的影响 ,数均分子量在数百至数千之间 .考察该共聚体系的动力学表明 ,该共聚反应速率对单体浓度呈一级关系     

氮氧自由基的研究——Ⅷ.关于溶剂极性经验参数的讨论

作者测定了有机溶剂-水二元混合溶剂体系中2,2,6,6-四甲基哌啶-1-氧自由基(TMPO)的ESRa_N 值.这类混合溶剂体系中 a_N-m 关系可归属有机二元混合溶剂体系的四种典型线型关系.比较了几种溶剂极性经验参数,说明各种经验极性参数-m 关系图的差异是特定模型反应中溶剂分子与溶质分子间相互作用不同的反映.对二元混合溶剂体系而言,a_N-E_T(30),a_N-Z 一般不具有线性关系,认为溶剂极性经验参数是溶剂(包括溶剂混合物)对模型化合物溶剂化能力的标度,给出了在各种溶剂体系中的 a_N 测定值,作为溶剂对中性偶极分子相对溶剂化能力的经验标度.     

六甲基磷酰胺在有机合成中的应用

综述了近20年来六甲基磷酰胺(HMPA)作为溶剂对有机反应的显著影响, 并着重总结HMPA所发生的化学反应及其在有机合成中的应用．     

水相有机反应研究新进展

近年来,以水作为溶剂的有机合成已成为一个研究热点.随着越来越多水相反应催化剂的发现,不断有相关的水相有机反应被报道.综述了近五年水相有机反应的最新进展.     

Comparison and optimisation of biodiesel production from <Emphasis Type="Italic">Jatropha curcas</Emphasis> oil using supercritical methyl acetate and methanol

In this study, biodiesel has been successfully produced by transesterification using non-catalytic supercritical methanol and methyl acetate. The variables studied, such as reaction time, reaction temperature and molar ratio of methanol or methyl acetate to oil, were optimised to obtain the optimum yield of fatty acid methyl ester (FAME). Subsequently, the results for both reactions were analysed and compared via Response Surface Methodology (RSM) analysis. The mathematical models for both reactions were found to be adequate to predict the optimum yield of biodiesel. The results from the optimisation studies showed that a yield of 89.4 % was achieved for the reaction with supercritical methanol within the reaction time of 27 min, reaction temperature of 358°C, and methanol-to-oil molar ratio of 44. For the reaction in the presence of supercritical methyl acetate, the optimum conditions were found to be: reaction time of 32 min, reaction temperature of 400°C, and methyl acetate-to-oil molar ratio of 50 to achieve 71.9 % biodiesel yield. The differences in the behaviour of methanol and methyl acetate in the transesterification reaction are largely due to the difference in reactivity and mutual solubility of Jatropha curcas oil and methanol/methyl acetate.     

Kinetic analysis for hydrothermal depolymerization of nylon 6

We investigated the influences of reaction temperature, time and water density. We also investigated the reaction rate and reaction scheme which is necessary to industrialize this process from the result of hydrolysis of nylon 6 in sub- and supercritical water. The reactions were carried out at temperatures between 573 and 673 K under the estimated pressures of up to 35 MPa (water amount charged in a reactor 0.83-3.79 g/5 cm³ - reactor) for reaction times of 5-60 min. The main products of hydrolysis of nylon 6 by sub- and supercritical water are ?-caprolactam and ?-aminocaproic acid. Based on our experimental results, the reaction scheme of nylon 6 decomposition is represented. Nylon 6 was decomposed into ?-aminocaproic acid by hydrolysis followed by cyclodehydration to ?-caprolactam or decomposition further to lower molecules. At each reaction conditions, the k₁ and k₂ values were determined and the activation energy was calculated.     

Two-step preparation for catalyst-free biodiesel fuel production

Biodiesel fuel was prepared by a two-step reaction: hydrolysis and methyl esterification. Hydrolysis was carried out at a subcritical state of water to obtain fatty acids from triglycerides of rapeseed oil, while the methyl esterification of the hydrolyzed products of triglycerides was treated near the supercritical methanol condition to achieve fatty acid methyl esters. Consequently, the two-step preparation was found to convert rapessed oil to fatty acid methyl esters in considerably shorter reaction time and milder reaction condition than the direct supercritical methanol treatment. The optimum reaction condition in this two-step preparation was 270°C and 20 min for hydrolysis and methyl esterification, respectively. Variables affecting the yields in hydrolysis and methyl esterification are discussed.     

脂肪酸在超临界甲醇中的酯化反应研究

超临界甲醇中的酯化和酯交换反应是利用植物油、动物油或废油脂制备生物柴油的新工艺.它的最大特点是不需要添加催化剂,超临界甲醇既是反应媒介,又是反应物.     

Synthesis of Rapeseed Biodiesel Using Short-Chained Alkyl Acetates as Acyl Acceptor

In this study, we conducted experiments using a response surface methodology to determine the optimal reaction conditions for the enzymatic synthesis of biodiesel from rapeseed oil and short-chained alkyl acetates, such as methyl acetate or ethyl acetate, as the acyl acceptor at 40 °C. Based on our response surface methodology experiments, the optimal reaction conditions for the synthesis of biodiesel were as follows: methyl acetate as acyl acceptor, catalyst concentration of 16.50%, oil-to-methyl acetate molar ratio of 1:12.44, and reaction time of 19.70 h; ethyl acetate as acyl acceptor, catalyst concentration of 16.95%, oil-to-ethyl acetate molar ratio of 1:12.56, and reaction time of 19.73 h. The fatty acid ester content under the above conditions when methyl acetate and ethyl acetate were used as the acyl acceptor was 58.0% and 62.6%, respectively. The statistical method described in this study can be applied to effectively optimize the enzymatic conditions required for biodiesel production with short-chained alkyl acetates.     

Green and mild oxidation: from acetate anion to oxalate anion

Abstract

A novel reaction system for the preparation of oxalate anion from cupric acetate and 2-(1H-imidazol-1-yl)-1,10-phenanthroline under green and mild reaction conditions is reported herein, namely, the methyl group from the acetate anion has been oxidized into a carboxyl group by air in the presence of Cu^II ion and 2-(1H-imidazol-1-yl)-1,10-phenanthroline at 0 to 30?°C. In the reaction, the Cu^II complex was formed with 1,10-phenanthrolin-2-ol and oxalate as ligands, in which 1,10-phenanthrolin-2-ol comes from the hydrolysis of 2-(1H-imidazol-1-yl)-1,10-phenanthroline and oxalate from the oxidation of acetate. The reaction system functions similarly to those of fungi.

The reaction system reported herein can oxidize methyl group into oxalate anion undergreen and mild reaction condition.     

纤维素在超临界水中的反应

纤维素是一种非常有价值的可再生资源,通过其反应可以获得多种有用的物质。对纤维素在超临界水中的反应进行了综述。在没有催化剂的情况下,纤维素在超临界水中水解生成葡萄糖、果糖、低聚物等;对纤维素水解的设备、产物分布以及纤维素水解反应机理进行了阐述。采用Ni,Pt,Ru,KOH等作催化剂,纤维素在超临界水中发生气化反应,生成的气体产物主要为H2,CO2和CH4;介绍了纤维素及其主要水解产物葡萄糖的制氢反应过程。对纤维素超临界水反应技术的发展前景进行了展望.     

Mechanisms and kinetics of noncatalytic ether reaction in supercritical water. 2. Proton-transferred fragmentation of dimethyl ether to formaldehyde in competition with hydrolysis

Noncatalytic reaction pathways and rates of dimethyl ether (DME) in supercritical water are determined in a tube reactor made of quartz according to liquid- and gas-phase 1H and 13C NMR observations. The reaction is studied at two concentrations (0.1 and 0.5 M) in supercritical water at 400 degrees C and over a water-density range of 0.1-0.6 g/cm3. The supercritical water reaction is compared with the neat one (in the absence of solvent) at 0.1 M and 400 degrees C. DME is found to decompose through (i) the proton-transferred fragmentation to methane and formaldehyde and (ii) the hydrolysis to methanol. Formaldehyde from reaction (i) is consecutively subjected to four types of redox reactions. Two of them proceed even without solvent: (iii) the unimolecular proton-transferred decarbonylation forming hydrogen and carbon monoxide and (iv) the bimolecular self-disproportionation generating methanol and carbon monoxide. When the solvent water is present, two additional paths are open: (v) the bimolecular self-disproportionation of formaldehyde with reactant water, producing methanol and formic acid, and (vi) the bimolecular cross-disproportionation between formaldehyde and formic acid, yielding methanol and carbonic acid. Methanol is produced through the three types of disproportionations (iv)-(vi) as well as the hydrolysis (ii). The presence of solvent water decelerates the proton-transferred fragmentation of DME; the rate constant is reduced by 40% at 0.5 g/cm3. This is caused by the suppression of low-frequency concerted motion corresponding to the reaction coordinate for the simultaneous C-O bond scission and proton transfer from one methyl carbon to the other. In contrast to the proton-transferred fragmentation, the hydrolysis of DME is markedly accelerated by increasing the water density. The latter becomes more important than the former in supercritical water at densities greater than 0.5 g/cm3.     

Chemical Reactions of Coumarins and Furocoumarins on Thin-Layer Chromatoplates

Most of the reaction achieved in this work were conducted with coumarin and furocoumarin. The reactions were performed on inert thin-layer chromatoplates under controlled conditions and the products of the reactions were compared as usual with the expected substances on the same chromatogram. The reactions performed were: mineral acid hydrolysis, methylation, acetylation, benzoylation, nitration and Schiff's bases on silica gel chromatoplates.