超临界流体中L-脯氨酸催化Aldol反应的研究

【作者】 刘玲；

【导师】 刘昭铁；

【作者基本信息】 陕西师范大学 ， 应用化学， 2009， 博士

【摘要】 近年来,脯氨酸及其衍生物等手性有机小分子催化剂在不对称合成中发挥着越来越重要的作用,受到人们越来越多的关注。其催化的不对称直接羟醛缩合反应（Aldol）都是在有机溶剂中进行的,反应中使用高沸点的溶剂（如DMF和DMSO）有利于提高产物的对映选择性,但产品的分离和纯化过程处理复杂,且有机溶剂的使用不利于环境保护。从绿色化学的角度出发,使用无毒,不易燃,可回收的物质作为反应溶剂,是绿色化学发展的一项重要目标。超临界流体如超临界二氧化碳（scCO₂）作为一类绿色溶剂越来越受到化学工作者的青睐。超临界流体与一般的有机液体溶剂相比,在传质、传热方面具有明显优势。scCO₂能使反应更高效、更清洁、易调控、绿色化进行,有利于减小或消除环境污染。基于超临界流体的溶剂效应可通过温度和压力有效调控的特性,以及scCO₂体系在手性不对称催化反应中的研究实践,并结合脯氨酸在催化手性不对称反应中,溶剂在其中发挥极其重要作用的研究结果,本论文考察了L-脯氨酸在超临界流体中的溶解行为,并以超临界流体为反应介质考察了L-脯氨酸催化丙酮与芳香醛的不对称直接Aldol反应的催化性能,具体开展了以下三方面的工作:1.本论文首先测定了scCO₂和1,1,1,2-四氟乙烷（HFC-134a）流体在不同温度和不同压力下的密度,并与P-R方程计算结果进行比较。结果表明,流体的密度与温度和压力的关系为非线性关系,scCO₂和HFC-134a流体的密度在压力一定时随着温度的升高而降低,温度一定时随着压力的升高而增加,表明流体的温度和压力是决定流体密度的重要因素,因此流体密度可通过温度和压力的改变来调节。固体溶质在超临界流体中的相平衡一直是超临界流体科学与技术研究的热点和难点。本论文对固体溶质L-脯氨酸在超临界流体中的相平衡进行了比较系统的研究。本论文采用静态法与重量分析法相结合测定了L-脯氨酸在HFC-134a和scCO₂流体中的溶解度,此法操作简便、除压力容器外不需要其他特殊装置。考察了压力、温度对溶解度的影响。测定了303～328 K,10～30 MPa下L-脯氨酸在scCO₂及HFC-134a流体中的溶解度。大大丰富了超临界流体相平衡基础数据。本论文用Chrastil方程关联计算了L-脯氨酸在scCO₂中的溶解度数据,实验值与计算值吻合良好。超临界流体中L-脯氨酸溶解度的测定为其在超临界流体中的催化反应奠定了基础。2.首次实现了超临界流体中L-脯氨酸催化的丙酮与芳香醛的不对称直接Aldol反应,ee值达到84%,本方法具有反应分离一体化的特点,简化了反应的后处理过程,实现了β-羟基酮的绿色合成,为类似有机合成反应的绿色化提供了很好的借鉴。以scCO₂流体为反应介质,考察了反应温度、压力、催化剂用量、反应时间、添加剂等因素对超临界流体中L-脯氨酸催化的丙酮与芳香醛的不对称直接Aldol反应的影响。结果表明,在scCO₂中的最佳反应条件为40℃,25 MPa,催化剂用量15 mol%,反应时间24 h,醛酮摩尔比1:15。以HFC-134a为反应介质时,考察了温度和压力对L-脯氨酸催化的Aldol反应的影响,并与在scCO₂中的结果进行了比较,结果表明,以HFC-134a为反应介质时,对映选择性较低。3.以叔丁氧羰基（Boc）保护的脯氨酸和取代的三氮唑为原料,合成了催化剂（S）-5-脯氨酰胺基三氮唑,以丙酮与对硝基苯甲醛的不对称直接Aldol反应为模板反应,考察了其催化Aldol反应的催化性能。考察了溶剂[聚乙二醇400（PEG-400）、曲拉通X-100（TX-100）、乙腈,N,N-二甲基甲酰胺（DMF）、四氢呋喃（THF）、二甲基亚砜（DMSO）、二氯甲烷（CH₂Cl₂）、氯仿（CHCl₃）]、催化剂用量（5-25 mol%）、反应温度（室温,0℃,-20℃）以及不同底物对催化剂催化Aldol反应的影响。实验结果表明,此催化剂在室温无溶剂、催化剂的用量为15 mol%条件下催化效果较好,Aldol产物的ee值最高达80%。为了进一步提高反应的对映选择性,本论文还考察了添加剂（如甲酸,L-苹果酸,L-酒石酸）对反应对映选择性的影响。催化剂是在室温无溶剂条件下完成催化反应的,避免了有机溶剂的使用,这使得反应在绿色条件下进行,在绿色化学迅速发展的今天,相信此催化剂将会得到更广泛的应用。更多还原

【Abstract】 In recent year,proline and its derivatives have been successfully used as chiral organocatalysts in asymmetric synthesis and have received extraordinary attentions.Most of the L-proline-catalyzed aldol reactions have been carried out in organic media such as DMF or DMSO. Purification process of products is very complex.Large amounts of organic solvents are used in chemical reactions,most of which are volatile,toxic,and flammable.From the viewpoint of greener processes,the use of non-hazardous and renewable materials is one of the most important goals of green chemistry.Supercritical carbon dioxide（scCO₂） is the most popular solvent among SCFs.The advantages of supercritical fluids（SCF） compared with conventional liquid solvents include low surface tension,high diffusivity,low viscosity and high compressibility.The reactions can carry out by a more efficient,clean,green method in scCO₂,which can reduce or eliminate environmental pollution.A number of physical parameters of supercritical fluid such as temperature and pressure can be effective regulated and controlled.Most research findings proved that solvent plays an important role in L-proline-catalyzed asymmetric aldol reactions,and some chiral asymmetric catalysis reactions were carried out in scCO₂ system.Based on these reasons,a static method coupled with gravimetric analysis was developed for measuring the solubility of L-proline in scCO₂ or HFC-134a,and L-proline-catalyzed asymmetric aldol reactions between ketones and aromatic aldehydes were carried out in scCO₂ or HFC-134a.This dissertation has undertaken the following work:1.The P-R equation is derived.Density of scCO₂ or HFC-134a at different temperatures and pressure was determined,and the results between derived by P-R equation and measured by experiment were compared.The results show that relationship between the fluid density and temperature or pressure is non-linear.The density of scCO₂ or HFC-134a decreased with the increasing of temperature and increased with the increasing of pressure.The temperature and pressure of fluids are important factors for density.The density of fluid can be adjusted by changing temperature and pressure of fluids.The equilibrium of solid in supercritical fluid is always indispensable to the development of supercritical fluid science and technology.Therefore,some works have been carried out.A static method coupled with gravimetric analysis was developed for measuring the solubility of L-proline in scCO₂ or HFC-134a.The appealing feature of this technique is its simplicity,and it requires no specialized equipment other than a suitable pressure cell.The effects of temperature and pressure on the solubility of L-proline were studied.The solubilities of L-proline in scCO₂ or HFC-134a were measured at condition of 303～328 K,10～30 MPa.In this paper,Chrastil equation was used to calculate the solubilities of L-proline in supercritical CO₂,experimental values are in good agreement with the calculated values.2.In this dissertation,the direct asymmetric aldol reaction between 4-nitrobenzaldehyde and acetone catalyzed by L-proline was successfully carried out in supercritical CO₂.The enantioselectivity of 84%ee to the targeted product was achieved.This offers a method for reaction-separation integration,and also the method simplifies the treatment process after the reaction.This provides a good foundation for the green organic synthesis.The effects of reaction temperature,pressure,the loading of catalyst,reaction time,additives and other factors on the L-proline-catalyzed asymmetric direct aldol reaction between acetone and aromatic aldehydes in scCO₂ or HFC-134a were investigated.The best reaction conditions in scCO₂ were at 40℃, 25 MPa,15 mol%amount of catalyst,the appropriate reaction time for 24 h,1:15 for molar ratio of aldehydes and ketones.However,HFC-134a as a reaction medium,the lower enantioselectivity was obtained due to the hydrogen bonds between F atoms and carboxyl in proline.3.Based on Boc-protected proline and substituted triazole as raw materials,a new catalyst （S）-5-prolylamide-triazole was synthesized and applied as catalysts for the direct asymmetric intermolecular aldol reaction.The effects of solvents,pressure,the loading of catalyst,additives, and reaction temperature on the asymmetric direct aldol reaction between acetone and aromatic aldehydes were studied.The experimental results show that the aldol reactions catalyzed by （S）-5-prolylamide-triazole carried out without solvent.The enantioselectivity of 80%ee to the targeted product was achieved at the 15 mol%catalyst loading.The addition of additives reduce catalytic performance of（S）-5-prolylamide-triazole.The reactions were finished without solvent at room temperature,which make reactions carried out in a green manner.We believe that this catalyst will be used widely.更多还原