ACYCLIC MECHANISM IN THE CLEAVAGE OF BENZILS WITH ALKALINE HYDROGEN-PEROXIDE

被引:69
作者
SAWAKI, Y [1 ]
FOOTE, CS [1 ]
机构
[1] UNIV CALIF LOS ANGELES, DEPT CHEM, LOS ANGELES, CA 90024 USA
关键词
D O I
10.1021/ja00515a023
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
The reaction of benzii with alkaline hydrogen peroxide in aqueous methanol gives benzoic acid and methyl benzoate; the yield of ester increases to 69% when H2O2is added gradually. The reaction in the presence of dimethyl sulfoxide gives the maximum yield (81%), close to that (87%) from the reaction of benzoic anhydride under the same conditions but in the absence of H2O2. These results rule out a dioxetane mechanism as the main pathway for the reaction of benzii but suggest that an anhydride is intermediate. 18O-Labeled hydrogen peroxide could be conveniently prepared by the t-BuOK-catalyzed autoxidation of benzhydrol in the presence of 18O2. The reaction of p-methoxy-and 2,4,6-trimethylbenzil with H218O2showed that one oxygen atom is incorporated in the carboxylic acid product but none in the ester. These results clearly eliminate a proposed epoxide mechanism but support a Baeyer-Villiger-type acyclic mechanism involving the migration of an acyl group with formation of an intermediate anhydride. Some of the anhydride appears to react with H2O2to form peroxy acid, which in turn oxidizes more benzii in a path which does not lead to ester. This reaction is blocked by the reduction of peracid by Me2SO. which accounts for the high ester yields when Me2SO is present. © 1979, American Chemical Society. All rights reserved.
引用
收藏
页码:6292 / 6296
页数:5
相关论文
共 36 条