Kinetic and mechanistic studies of the oxidation of mandelic acid and nine monosubstituted mandelic acids by benzimidazolium dichromate (BIDC) in dimethyl sulfoxide are discussed with an emphasis on correlation of structure and reactivity. The reactions were of first order with respect to BIDC. However, Michaelis-Menten type kinetics were observed with respect to hydroxy acids. The reactions are catalysed by protons. The deuterium isotope effect for the oxidation of mandelic acid (kH/kD = 5.91 at 298 K) indicated an α-C-H bond cleavage in the rate-determining step. An analysis of the solvent effect showed that the role of cationsolvation is major. The reaction showed an excellent correlation with the Hammett σ values, the reaction constant being negative. Based on the kinetic data, analysis of the solvent effect and results of structure-reactivity correlation along with some non-kinetic parameters, a mechanism involving rate-determining oxidative decomposition of the complex through hydride-ion transfer via a cyclic transition state to give the corresponding oxoacid is suggested.

中文翻译：

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苯并咪唑鎓重铬酸盐氧化某些α-羟基酸的反应动力学及相关性分析

讨论了苯并咪唑重铬酸盐 (BIDC) 在二甲基亚砜中氧化扁桃酸和九种单取代扁桃酸的动力学和机理研究，重点是结构和反应性的相关性。反应是关于 BIDC 的一级反应。然而，观察到关于羟基酸的 Michaelis-Menten 型动力学。反应由质子催化。扁桃酸氧化的氘同位素效应 (kH/kD = 5.91 at 298 K) 表明在速率决定步骤中发生了 α-CH 键断裂。溶剂效应的分析表明，阳离子溶剂化的作用是主要的。该反应与哈米特 σ 值显示出极好的相关性，反应常数为负。根据动力学数据，