【作者】 李智；

【导师】 何静；

【作者基本信息】 北京化工大学 ， 化学工程与技术， 2011， 硕士

【摘要】 脯氨酸及其衍生物是最重要的一类有机小分子催化剂之一。如何实现脯氨酸类催化剂对直接不对称Aldol反应的高效催化更是不对称催化领域的研究热点。近年来,脯氨酸多相化后催化直接不对称Aldol反应备受关注,然而多相脯氨酸催化剂催化不对称Aldol反应效率普遍较低。本论文设计制备了一种具有亲疏水周期交替分布孔壁的介孔材料负载脯氨酸多相催化剂,研究了多相催化剂对不对称Aldol反应的催化性能,并以疏水孔壁和亲水孔壁的介孔材料负载脯氨酸多相催化剂为对比催化剂,研究了多相催化剂表面性质对催化性能的影响。通过XRD和N2吸脱附等手段表征了介孔载体的有序结构并通过元素分析、FT-TR等手段证明了均相脯氨酸在介孔材料内表面的负载,用29Si NMR、动态水分吸附等手段表征了催化剂载体的不同表面性质。最后以环己酮和对硝基苯甲醛在无有机溶剂条件下的直接不对称Aldol反应为评价反应,研究了催化剂表面性质和孔道内反应微环境对催化剂催化不对称Aldol反应的影响。我们的研究证明：1.多相催化剂表面性质影响催化活性,多相催化剂介孔孔壁促进有机反应物靠近催化剂活性中心,有效的提高了反应转化速率。不同亲疏水表面的催化剂对反应底物的吸附能力不同,孔壁疏水性越强,催化剂对反应速率的促进越明显。亲疏水交替催化剂能有效催化无溶剂条件下均相脯氨酸不能催化的直接不对称Aldol反应。2.当反应在水溶剂条件下进行时,催化剂孔壁富集反应底物进入孔道,反应速率相对于无溶剂时更大,且孔道内有效的油水界面能够进一步提高催化剂催化活性。相对于疏水催化剂孔道内形成的连续凹形油水界面和亲水催化剂孔道内不能形成有效油水界面,亲疏水交替催化剂孔道内形成的不连续凸形油水界面对反应速率的促进更大。3.相对于脯氨酸及其衍生物的均相催化,多相催化剂孔道限域效应导致不对称Aldol反应主要产物构型反转。对于三种不同表面性质的多相催化剂,活性中心在孔道内的存在位置不同,但三种载体都能够通过限域效应抑制反应醛底物从re面进攻anti-酮烯胺,从而提供产物的不对称选择性,造成主要产物构型反转。亲疏水交替催化剂相对于疏水催化剂和亲水催化剂限域效应更大,产物不对称选择性更高。4.界面协同提高不对称Aldol反应不对称选择性。孔道内有效油水界面的存在有利于界面自由羟基通过氢键吸引反应底物或者参与过渡态促进底物醛从si面进攻syn-酮烯胺,增大反应速率的同时提高产物不对称选择性。催化剂不同的表面性质能够影响孔道内油水界面的存在形式。相对亲疏水交替催化剂孔道内形成的不连续凸形油水界面,疏水催化剂孔道内形成的连续凹形油水界面阻碍底物醛从si面进攻syn-酮烯胺,降低反应的不对称选择性。更多还原

【Abstract】 Proline and its derivatives are one class of the most important small organic-catalysts. How to achieve their highly efficient catalysis in direct asymmetric Aldol reactions becomes a hot spot in the field of asymmetric reaction. In recent years, heterogeneous proline catalyst has been followed with enormous interest in the catalytic to direct asymmetric Aldol reactions. However, the catalysis of heterogeneous proline in asymmetric Aldol reaction has generally low efficiency and/or enantioselectivity.We prepared a heterogeneous catalyst that proline immobilized on mesoporous silica with with periodically alternating hydrophobic and hydrophilic blocks. The catalysis of heterogeneous catalyst to the asymmetric Aldol reaction were studied, for comparison, the heterogeneous catalysts with hydrophobic surface and hydrophilic surface were prepared. The effect of the surface properties of heterogeneous catalysts to the catalytic properties was studied. The ordered structure of mesoporous materials were characterized by the measures of XRD, N2 adsorption-desorption, and so on. The immobilized of proline on mesoporous materials were characterized by the measures of elemental analysis and FT-IR, et al. The surface properties of the different catalysts were characterized by the measures of Si NMR and dynamic moisture sorption. The Aldol reaction of p-nitrobenzaldehyde and cyclohexanone without organic solvents was performed to research the catalytic ability of the heterogeneous catalysts. Our studies have shown that:1. The surface properties of the heterogeneous catalysts affect the catalytic activity. The pore walls of mesoporous heterogeneous catalysts promote the organic reactants near the active sites of catalysts, thereby effectively improving the conversion rate of the Aldol reaction. The heterogeneous catalysts with different surface have different adsorption capacity to reaction substrate. The more hydrophobic of the pore walls, the improvment of catalyst to the reaction rate is more evident. The periodically alternating hydrophobic and hydrophilic catalyst can effectively catalyze the direct asymmetric Aldol reaction in solvent-free condition which can not be catalyzed by homogeneous proline.2 When the reaction progressed in aqueous media, the pore walls of the catalysts enriched the reaction substrates into the channels, the reaction was much faster than the reaction progressed in solvent-free condition. The effective oil-water interface in the channels of catalysts can further improved the catalytic activity. Compared to the concave continuous oil-water interfaces in the channels of hydrophobic catalyst and the invaid oil-water interface in the channels of hydrophilic catalyst, the convex discontinuous oil-water interfaces in the channels of the periodically alternating hydrophobic and hydrophilic catalyst have more powerful improve to the reaction rate.3 Compared to the homogeneous catalysis of proline and its derivatives, the catalysis of heterogeneous catalysts had an configuration inversion of the major product for the asymmetric Aldol reaction due to the confinement effect. The active sites presence in different positions in the channels of three different heterogeneous catalysts, but the pore walls of three class of heterogeneous catalysts all hindered the aldehyde re attack on anti-enamine, leading to the favored production of inverse isomers. The catalyst with periodically alternating hydrophobic and hydrophilic surface has more powerful confinement effect than the catalysts with hydrophobic and hydrophilic surface, leading to higher enantioselectivity.4 The oil-water interface in the channels of catalysts enhance the enantiomer excess of the reaction. When there was an effective oil-water interface in the channels of catalysts, the si attack on syn-enamine is supposed to be further favored due to the hydrogen bonds of the free OH group of the interfacial water with the reactants and transition state, giving good yield and high enantioselectivity. The properties of the surfaces of catalysts affect the shape of the oil-water interface. In the channels of hydrophobic catalyst forming a concave continuous oil-water interface, and in the channels with with periodically alternating hydrophobic and hydrophilic surface forming a convex intermittedt oil-water interface. The continuous concave interface lowers the stability of the transition state for (2R, 1’S) isomer due to the interaction of phenyl ring with water, leading to the decrease of the enantioselectivity.更多还原