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

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=OCH₃,CH₃,H,Cl,NO₂)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:ΔH_dl-meao= - 18.02 kJ/mol, ΔS_dl-meao= - 26.51 J/mol·K, ΔH^≠ = 151.78 kJ/mol, ΔS^≠ = 71.64 J/mol·K.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.

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

The kinetics were studied for the thermal isomerization of meso-diethyl 2,3-dicyano-2,3-di (p-Xsubstituted phenyl) succinates (X = H) in melten state and the EPRspectra 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 Kreduced as the rise of the reaction temperature.The active parameters were found to be ΔH_dl-meao= - 18.02 kJ/mol, ΔS_dl-meao= - 26.51 J/mol·K, ΔH^≠ = 151.78 kJ/mol, ΔS^≠ = 71.64 J/mol·K.dl-Isomer is more stable than the corresponding meso-iscmer.