草酸二乙酯与苯酚酯交换反应的热力学分析

针对草酸二乙酯与苯酚酯交换反应过程,采用Benson基团贡献法,计算了草酸二乙酯与苯酚酯交换反应中各反应物的标准摩尔生成焓、标准摩尔熵和摩尔等压热容;采用Trouton经验规则计算得到了乙基苯基草酸酯和草酸二苯酯沸点下的蒸发焓;计算了草酸二乙酯与苯酚酯交换反应的焓变、熵变、吉布斯自由能变和平衡常数。计算结果表明,草酸二乙酯与苯酚酯交换反应为吸热反应,升高温度有利于草酸二苯酯的生成;草酸二乙酯与苯酚酯交换反应的平衡常数很小,必须及时移出副产物乙醇打破平衡限制,提高草酸二苯酯的收率;中间产物乙基苯基草酸酯歧化反应的平衡常数要比乙基苯基草酸酯与苯酚反应的平衡常数大很多,故草酸二苯酯主要是由乙基苯基草酸酯歧化生成。

Thermodynamic Analysis of Transesterification of Phenol with Diethyl Oxalate

Thermodynamic data for transesterification of phenol with diethyl oxalate(DEO),namely standard molar formation enthalpy,standard molar entropy and molar heat capacity of the reagents under constant pressure were evaluated by Benson group contribution method.Vaporization enthalpies of ethyl phenyl oxalate(EPO) and diphenyl oxalate(DPO) at boiling points were calculated by Trouton rule.The changes of enthalpy,entropy and Gibbs free energy,and equilibrium constant of transesterification of phenol with DEO could be obtained.The results indicated that the transesterification is endothermic.Raising of reaction temperature will be propitious to synthesis of DPO.Equilibrium constant of the transesterification is relatively small,for improving the yield to DPO,the by-product enthanol must be distilled out right away from the system to break the equilibrium state and move the reaction forward.Equilibrium constant of the disproportionation of EPO into DPO is much larger than that of transesterification of EPO with phenol,so DPO mainly produces via disproportionation of EPO.