维生素A醋酸酯热处理下结构变化研究

Structure stability of vitamin A acetate in heating

通过模拟生产工艺及存储条件,考察维生素A醋酸酯在避光、无氧时热处理条件下的变质情况,研究产物的可能结构及副产物类型.结果表明,维生素A醋酸酯主要发生由热引发的异构化和Diels-Alder环合二聚反应,通过GPC、HPLC-DAD、LC-MS分析检测得到产物结构.利用TS方法计算并比较各维生素A醋酸酯异构体进行二聚反应所需的活化能,得到Diels-Alder反应生成二聚物的环合反应过程为:一分子全反式维生素A醋酸酯经异构化为顺式异构体,该异构体作为亲双烯体与作为双烯体的另一分子全反式维生素A醋酸酯进行反应生成二聚体.利用含微扰效应的分子前沿轨道理论计算区域选择性不同的二聚体的生成微扰能变化值,得到最可能的6种二聚体结构.

The heat-induced degeneration products of vitamin A acetate and the plausibl analyzed under oxygen-free and light-free condition that vitamin A acetate was processed e mechanism were stored and used. GPC,HPLC-DAD and LC-MS results showed that two reactions, namely isomerization and Diels-Alder reaction, were predominated in this process. The activation energy of the Diels-Alder reaction between various vitamin A acetate isomers was calculated with the transition state theory. Results showed that the dimers were mainly produced by the Diels-Alder reaction between trans-vitamin A acetate （act as diene） and cis-vitamin A acetate （act as dienophile）, where cis-vitamin A acetate was the isomerization product of trans-vitamin A acetate. The most probable structures of the six dimers were presented by comparing the energy change in perturbational molecular orbital theory for different regioselectivity of the Diels-Alder reaction.