用吡嗪鎓氯铬酸盐进行的醇类氧化反应及其动力学研究

On the kinetics and oxidation reaction of alcohols using pyrazinium chlorochromate

在6MHCl溶剂中,用吡嗪和三氧化铬合成出吡嗪翰氯铬酸盐(PyzCc),并用IR、EA、ICP 证实其结构。在酸催化的N．N-二甲基甲酰胺溶剂中,用PyzCc有效地氧化苄醇及其衍生物(P-CH3、 H、m-Br、m-NO2)。本实验中,吸电子基使反应速度减小,而供电子基使反应速度增加。Hammett反 应常数P值为-0．68(308K时)。由此可知,利用PyzCc的醇氧化反应经历先生成铬酸酯的过程后在定速 步骤发生质子转移的反应历程。

Pyrazinium chlorochromate (PyzCc ) is synthesized by the reaction of pyrazine with chromium (VI) trioxide in 6M HC1. Its structure is verified by IR, EA and ICP. In the presence of hydrochloric acid (HC1) , PyzCc oxidizes benzyl alcohol and its derivatives (P - CH3, H, m - Br, m - NO2) smoothly in N, N - dimethyl-formamide solvent. Electron - donating subsistent accelerates the reaction, whereas elctron - withdrawing groups retarded the reaction. The Hammett reaction constant, ρ is -0. 68 at 303K. The results show that the proton transfer occurs after the prior formation of a chromate ester in the rate - determining step.