离子液体/季铵盐辅助氯过氧化物酶促氧化合成聚酚

Enzymatic Polymerization of Phenols Catalyzed by Chloroperoxidase in the Presence of Ionic Liquids/Quaternary Ammonium Salts

基于氯过氧化物酶(CPO)催化氧化苯酚衍生物单体,建立了一个聚酚的绿色合成体系.以对苯基苯酚、对甲基苯酚、4-乙基苯酚、对羟基肉桂酸、对异丙基苯酚和邻甲基苯酚等6种底物为考察对象,以聚合物的产率、聚合度及热稳定性为评价指标,研究了体系中引入离子液体(ILs)或季铵盐(QAS)以及底物结构和反应微环境等对聚合反应和聚合物性质的影响.结果表明,引入少量咪唑类ILs或QAS可有效提高产物收率,其中ILs/QAS的阳离子基团越大和疏水链越短,越有利于酶催化聚合反应的进行;而ILs/QAS添加量的影响则呈现"钟罩"型规律.同时,苯酚对位取代远比邻位取代有利于聚合反应进行;而对位取代基中烷基类给电子基团比芳香基取代更有优势,所得聚合物的聚合度和热稳定性相对增大,但随着取代基团的增大,其空间位阻不利于聚合物产率的提高;反应体系的p H应控制在弱酸性至近中性,以避免竞争性的副反应的发生;而氧化剂H_2O_2则需要采用间歇式加入以抑制瞬时过浓导致CPO活性中心卟啉环的氧化损伤.基于CPO的活性中心结构分析了聚合机理.

A green enzymatic approach for the synthesis of phenol polymersfrom substituted phenols monomer by chloroperoxidase（ CPO）-catalyzed H2O2-oxidation was proposed in this paper. The yield and thermal stability of polymers of p-methyl phenol,p-ethyl phenol,p-propyl phenol,p-phenyl phenol and p-hydroxy-cinnamic acid were studied based on the presence of imidazolium-based ionic liquids（ ILs） or quaternary ammonium salts（ QAS）,the effect of structure of the substrates and the reaction microenvironment. The results showed that the introduction of little amount of ILs/QAS can improve the production of polymerization of phenols efficiently,in which ILs/QAS with bigger cation group and shorter hydrophobic chain was much more effective,while the influence of ILs/QAS amount on polymerization of phenols showed a ＂ball type＂pattern. Moreover,it was found that p-substituted phenol and electron-donating group were more beneficial to the increase of yield and thermal stability of phenol polymers compared to o-substituted phenol and electron-withdrawing group.However,the steric hindrance was increased with the increasing size of substituent group,which was not beneficial to the polymerization of phenols. The p H value should be controlled as weak acid or even near-neutral to avoid competitive side reaction,while the adding of H2O2 should be in a batch type to suppress the oxidative damage of heme caused by the instantaneous concentrated H2O2. The mechanism of polymerization was also analyzed and proposed based on the characteristics of structure of CPO active site.