Kinetics and Mechanism of Nucleophilic Displacement Reactions of Y-Substituted Phenyl Benzoates with Z-Substituted Phenoxides

Bulletin of the Korean chemical society

Se Won Min¹  Ik Hwan Um¹  Jin A Seo¹ 

关键词: Acyl-group transfer;    Aryl benzoates;    Br©ªnsted-type plot;    Concerted mechanism;    Yukawa-Tsuno plot;   

DOI  :  

学科分类：化学（综合）

来源: Korean Chemical Society

【 摘 要 】

Second-order rate constants have been measured for two series of nucleophilic displacement reactions, i.e., reactions of 4-nitrophenyl benzoate with Z-substituted phenoxides and those of Y-substituted phenyl benzoates (1a-h) with 4-chlorophenoxide (4-ClPhO^-) in 80 mol% H₂O/20 mol% DMSO at 25.0 �? 0.1�?. The Br┆nsted-type plot for reactions of 4-nitrophenyl benzoate with Z-substituted phenoxides exhibits an excellent linear correlation with �?_nuc = 0.72. Reactions of 1a-h with 4-chlorophenoxide result in also a linear Br┆nsted-type plot with �?_lg = -0.62, a typical �?_lg value for a concerted mechanism. The Hammett plots correlated with ヲo and �?- constants show many scattered points for reactions of 1a-h with 4-chlorophenoxide. In contrast, the corresponding Yukawa-Tsuno plot exhibits an excellent linear correlation with ヱY = 2.26 and r = 0.53, indicating that expulsion of the leaving group occurs at the rate-determining step (RDS) either in a concerted mechanism or in a stepwise pathway. However, a stepwise mechanism with leaving group departure being the RDS is excluded since the leaving Y-substituted phenoxide is less basic and a better nucleofuge than the incoming 4-ClPhO^-. Thus, the reactions have been concluded to proceed through a concerted mechanism, in which bond formation between the nucleophile and electrophilic center is more advanced than expulsion of the leaving group in the transition state on the basis of the magnitude of モnuc and モlg values.

【 授权许可】

Unknown