Meso-2,3-二氰基-2,3-二苯基丁二酸二乙酯熔融相热异构化反应动力学及中间体EPR测定

Kinetics of Thermal Isomerization of meso-Diethyl 2,3-Dicyano-2,3-Diphenyl Succinate and the EPR Spectra of the Intermediate in Melten State

测定了2,3-二氰基-2,β-二苯基丁二酸二乙酯meso-异构体熔融相的热异构化反应动力学及苯环对位为X(X=OCH_3,CH_3,H,Cl,NO_2)的相应二乙酯反应中间体自由基的EPR谱,自由基的结构由计算机模拟确定.结果表明,在实验温度范围内,平衡常数随温度的升高而降低.热力学数据为:.反应机理是内消旋体的中心碳-碳键发生均裂,生成α-氰基-α-乙氧甲酰基-P-X取代苄基自由基,再重新结合时发生异构化,生成dl-异构体.

The kinetics were studied for the thermal isomerization of meso-diethyl 2,3-dicyano-2,3-di (p-X substituted phenyl) succinates (X = H) in melten state and the EPR spectra of the intermediates (X = OCH3, CH3, H, Cl, NO2) were observed. The central carbon-carbon bond of the five isomers was homolysed to give ethyl α-cyano-α-ethoxycarbonyl-p-substituted benzyl radicals. The structures of the intermediates were determined by compute simulation. The kinetic results indicate that the equilibrium constant K reduced as the rise of the reaction temperature. The active parameters were found to be ΔHdl-meao = - 18. 02 kJ/mol, ΔSdl-meao = - 26. 51 J/mol f33K, ΔH≠ = 151. 78 kJ/mol, ΔS≠ = 71. 64 J/mol · K. dl-Isomer is more stable than the corresponding meso-iscmer.