诱导效应指数在多相催化中的应用——Ⅰ.醇类分子结构与其脱水反应速度的关系

APPLICATION OF THE INDUCTIVE-EFFECT INDEX TO HETEROGENEOUS CATALYTIC REACTIONS——I. THE RELATION BETWEEN MOLECULAR STRUCTURE OF ALCOHOLS AND THE RATE OF CATALYTIC DEHYDRATION

关于诱导效应指数在多相催化中的应用问题还很少有人讨论,我们设想,只要严格保持一定的条件,例如在同一催化剂上,反应控制步骤相同,动力学型式相同,诱导效应为反应的主导因素等,诱导效应指数的一些基本规律也应该适用于多相催化反应,我们试借醇类多相催化脱水反应的研究以证明这种设想,并由诱导效应指数与催化活性的关系,讨论醇类在辉县黑干土催化剂上的反应机理.

The kinetics of the catalytic dehydration of ethyl,n-propyl,n-butyl,iso-butyl,sec-butyl,and tert-butyl alcohols on the catalysts made of black earth of Hui-Hsien,Honan Province have been studied.All these reactions are of first order.Their energies of activation were evaluated.When the inductive effect indices of R in ROH were plotted against the logarithms of rate constants,good straight lines were obtained.Both the slopes and intercepts of these lines for each temperature were linearly related to the reciprocal of absolute temperature.Linear relationship was also obtained between the inductive effect indices of R in ROH and the energies of activation.The plot of percentage conversion against the inductive-effect indices gave an S-shaped curve.Linear relationship was also obtained for the inductive-effect indices and the energies of activation of the dehydration reaction of various alcohols on AlOcatalysts.This indicates that for the same catalyst with the same rate-controlling steps and the same type of kinetic scheme,and when the inductive effect plays a leading role in the reactivity,the general principle of inductive-effect index is also applicable to heterogeneous catalytic reactions.Based on the principle of the inductive-effect index a probable mechanism of the dehydration reaction of alcohols on the catalyst used was deduced,that is,the C-O bond breaks first on the surface of the catalyst.