有机碱催化天然磷脂制备L-α-甘油磷脂酰胆碱（GPC）酯交换反应的研究

【作者】 李红亚；

【导师】 张小里；

【作者基本信息】 西北大学 ， 化学工程， 2013， 博士

【摘要】 L-α-甘油磷脂酰胆碱(简称GPC)作为一种重要的神经递质和磷脂前体,可通过各种方式参与人体生物化学代谢,对神经系统、生殖系统、内分泌系统等均有重要作用,具有提高人类认知能力、抵抗肌肉萎缩、抗衰老、加快因手术所引起的脑损伤恢复等功效。GPC作为一种医药保健品及功能性食品,其最可靠的制备方法是天然磷脂(天然来源的磷脂酰胆碱(PC))酯交换脱脂肪酰基法,但是传统的无机碱催化酯交换反应过程存在副反应多、乳化现象严重、产物分离困难、原料品质要求苛刻、废水产生量大等缺点。本文利用有机碱催化剂作用条件温和,易于获得等优点,探索采用其催化天然PC酯交换脱脂肪酰基制备GPC,系统地研究催化剂种类和反应条件,分析反应过程的竞争关系,归纳反应的动力学、热力学规律,为工业应用提供预测反应过程的参考,同时为深入地认识此类反应提供理论支持。探索将低沸点有机胺用于催化天然PC酯交换脱脂肪酰基反应制备GPC的过程中,筛选出了正丙胺、异丙胺和叔丁胺三种催化活性较高的低沸点胺,系统研究了其催化酯交换制备GPC的工艺条件。研究发现叔胺类催化剂的活性较差,且对于同分异构体而言,支链胺比直链胺的活性高；对于直链胺,其催化活性随碳原子数的增多而降低。在正丙胺、异丙胺和叔丁胺催化酯交换反应制备GPC的过程中表现出基本类似的规律：当体系中催化剂用量为2.4%,磷脂酰胆碱浓度为0.05-0.10mol/L,反应温度为60℃,反应时间为260分钟时,PC转化率和GPC收率均较高,其中异丙胺催化反应时活化能最小。此外优选的低沸点胺催化剂可以与甲醇一起蒸馏回收,再次循环使用时仍具有较高的活性。通过GC和1HNMR分析发现所得产物纯度较高,且过程中无副反应发生。研究了低沸点胺催化酯交换反应制备GPC的反应机理及动力学,发现胺引发烷氧基进攻羰基碳的机理能较好地描述该反应过程,同时依此所推导出的二级动力学与实验结果吻合良好。研究季铵碱相转移催化剂催化酯交换反应制备GPC,探索发现了氢氧化胆碱作为催化剂的良好性能,并对氢氧化四丁基铵和氢氧化胆碱催化反应的工艺条件进行了比较研究。在搅拌速率为500rpm、氢氧化四丁基铵用量为0.015mol/L、反应温度为40℃、反应物料比为30：1、反应时间120分钟时,PC转化完全,反应效果较好。在其他条件相同的情况下,若要达到类似的反应效果,氢氧化胆碱的用量仅需0.012mol/L。该类催化剂不仅降低了反应温度,缩短了反应时间,而且氢氧化胆碱本身作为食品中常用的添加剂,即使在产物中有少量残留也不会影响其安全使用。对季铵碱相转移催化酯交换反应制备GPC的反应机理及动力学进行了探讨,其中相转移催化过程可由Starks萃取模型描述,而拟一级动力学能较好关联实验数据,在氢氧化四丁基铵和氢氧化胆碱的催化下反应活化能分别为32.0和30.5kJ/mol。探索研究季铵碱相转移催化剂的固载化,以C1-C4的直链叔胺与氯甲基聚苯乙烯季铵化反应制备得到系列固载化季铵碱催化树脂,并尝试用于催化天然PC酯交换反应制备GPC。优化了催化剂的制备条件和酯交换反应的工艺条件。在以1,4-二氧六环为溶剂、三乙胺为胺化剂、60℃下反应180分钟得到的固载化季铵碱树脂TEABR具有较好的催化活性。在搅拌速度为675rpm、催化剂用量为80g/L、反应温度为60℃、PC浓度为0.15mol/L、反应时间210分钟时,TEABR催化酯交换反应的PC转化率可达到99%,同时GPC收率可达88.3%。固载化季铵碱催化树脂不仅简化了GPC的制备工艺,改善了均相催化中产物分离和催化剂回收困难等问题,而且其活性及稳定性良好,在酯交换制备GPC过程中重复使用10次后其活性基本未现衰减。对PC与甲醇酯交换反应过程的热力学行为进行了模拟。结果表明,第一步由PC酯交换脱脂肪酰基生成溶血磷脂酰胆碱(LPC)的反应为吸热反应,升高温度有利于反应的进行；同时该步反应△Gθ(T)为正值,不能自发进行。而第二步由LPC再次脱脂肪酰基生成GPC的反应为放热反应,降低温度有利于反应的进行,△Gθ(T)为负值,此步反应可自发进行。酯交换脱脂肪酰基生成GPC的两步反应中,升温、增加醇浓度启动第一步反应为全过程进行的关键。对负载季铵碱催化剂TEABR树脂催化磷脂酰胆碱与甲醇酯交换的多相反应动力学进行了研究,并分别建立了以甲醇吸附、表面反应和产物脱附为控制步骤的动力学模型。通过对模型参数的估计和实验数据的模拟发现：以表面反应为控制步骤的模型能较好地描述反应过程,理论计算与实验数据比较吻合。该研究结果可为GPC的工业化生产提供重要的理论指导。更多还原

【Abstract】 As an important neurotransmitter and phospholipid precursor, L-a-glycerophosphocholine (GPC) can support human health through a variety of mechanisms, it has important roles in the nervous system, reproductive system and endocrine system, et al. GPC has myriad functions for improving people’s cognitive ability, resisting muscle atrophy and aging, speeding up the recovery of brain damage caused by surgery. As a medicine product and functional food, the most acceptable method for preparing GPC is to remove fatty acyl from natural lecithin (natural source of phosphatidylcholine (PC)) by transesterification. However, there are many problems existed in the conventional inorganic base-catalyzed transesterification, such as the more side reactions, serious emulsification, difficulties in separation, high quality requirement for the materials, and the large amount of wastewater produced during the processes. In this paper, the organic base catalysts were used instead of the inorganic ones to prepare GPC, because these catalysts were accessible, and the reactions could performed under mild conditions. The reaction conditions were studied in details for each kind of catalyst, and the competition in the process, the reaction kinetics and thermodynamics rules were analyzed, in order to provide a reference for predicting reaction process for industrial applications and a theoretical support for in-depth understanding of such reactions.Series of low boiling point organic amines were used in the catalytic transesterification of natural PC for preparing GPC, the n-propylamine, isopropylamine and tert-butylamine with better activities among the amines were selected and used in the deacylation reaction. It was found that the activity of tertiary amines were poor; and for the isomers, the branched amines showed better activity than the normal amines; for normal alkylamines, the activity decreased with the increase of carbon numbers. The n-propylamine, isopropylamine and tert-butylamine showed similar laws in the deacylation process:when the amount of catalyst was2.4%, concentration of phosphatidylcholine (PC) was0.05-0.10mol/L, reaction temperature was60℃, reaction time was260minutes, both the conversion of PC and yield of GPC were higher, and the reaction activation energy was minimum catalyzed by isopropylamine. In addition, the low boiling point amines can recovered by distillation combined with the recovery of methanol, they could get similar effect to the fresh catalyst after repeatedly used. GC and1H NMR were used to analyze the product, it was indicated that the product had high purity and there was no side reaction between the catalyst and other materials. The mechanism and kinetics of the transesterification catalyzed by the low boiling point amines were studied. It was find that the reaction can be better described by the alkoxy anion mechanism, and the second-order kinetics model deduced from the mechanism was in good agreement with the experimental results.The transesterification catalyzed by quaternary ammonium base phase transfer catalyst was studied, and the choline hydroxide showed good performance in the process, then the reaction conditions of the transesterification catalyzed by tetrabutylammonium hydroxide and choline hydroxide were studied comparatively. With tetrabutylammonium hydroxide, PC reacted completely after260minutes under a stirring speed of500rpm, catalyst amount of0.015mol/L, reaction temperature of60℃, and molar ratio of methanol to PC was30:1. With the same conditions, when choline hydroxide used as catalyst, PC could react completely under the catalyst amount of0.012mol/L. This kind of catalyst reduced the reaction temperature and shortened the reaction time, especially for choline hydroxide, which used as a food additive, it can not affect the safe use of GPC even a small amount of residue in the product. The mechanism and dynamic model of the transesterification catalyzed by quaternary ammonium base phase transfer catalyst were discussed, it was found that the catalysis process can be described by the Starks extraction model, and the pseudo-first-order kinetics model associated with the experimental data well, the reaction activation energies were32.0and30.5kJ/mol respectively with tetrabutylammonium hydroxide and choline hydroxide.The immobilization of quaternary ammonium base phase transfer catalyst was researched, and a series of quaternary ammonium base resins were prepared from chloromethyl polystyrene and different tertiary amine, the resins were attempted to be used in the catalytic transesterification for preparing GPC from natural PC. Both the resin preparation conditions and the reaction conditions of the transesterification were optimized. The results demonstrated that the resin had better catalytic activity under the conditions of:1,4-dioxane as solvent, triethylamine as aminating agent, temperature was60℃and amination time was3h. With the prepared TEABR resin, the conversion of PC can reach99%, while the yield of GPC was88.3%with the conditions of:the stirring speed was675rpm, amount of catalyst was80g/L, reaction temperature was60℃, concentration of PC was0.15mol/L, and reaction time was210minutes. The use of quaternary ammonium resin as a promising heterogeneous catalyst simplified the craft and minimized the problems existed in the homogeneous catalytic process, and the activity and stability of the catalyst were almost invariant after repeated10times.Thermodynamic behavior of the transesterification between PC and methanol was carried out. The results showed that the first step of the transesterification for generating lysophosphatidylcholine (LPC) was endothermic, and higher temperature favored the progress of the reaction; while this step did not occur spontaneously because the AGθ(T) was positive. The second step for generating GPC from LPC was exothermic, and lower temperature favored this reaction; while the AGeθ(T) was negative, this step can be carried out spontaneously. Elevating the reaction temperature to start the first reaction was the key step during the transesterification, so higher temperature and alchols concentration favored the formation of GPC.The heterogeneous reaction kinetics of the transesterification catalyzed by TEABR resin was studied, and the kinetic model was proposed respectively when methanol adsorption, surface reaction and product desorption as the rate-determining step. From the models the kinetic parameters were estimated, the results demonstrated that the experimental data fit the model better than others when the surface reaction was the rate-determining step, and this model was reliable enough to provide an important guidance for the industrial production of GPC.更多还原