Micellar Catalysis of Organic-Reactions. XXI. A Comparison of the Catalytic Activity of Micelles of Cetyltrimethylammonium Bromide and Sulfate on Ester, Amide and Carbamate Hydrolyses

Abstract

The basic hydrolyses of phenyl acetate, N,4-dimethyl-N-(3′- nitrophenyl ) benzamide , methyl N-methyl-N-(4′-nitrophenyl) carbamate and methyl N-(3′,5′-dinitrophenyl)-N-methylcarbamate have been studied in cationic micelles of cetyltrimethylammonium bromide (ctab) and sulfate (ctas). Hydrolysis of phenyl acetate and the 4′-nitro carbamate, which involve rate-determining hydroxide attack, exhibit weak catalysis by both micelles, and the observed rates in each micelle are similar. The hydrolysis of the benzamide and the 3′,5′-dinitro carbamate, which involve rate determining C-N bond breaking, show larger catalysis, and, furthermore, micelles of ctab are more effective than micelles of ctas. The observed rates can be explained by the pseudo-phase kinetic model.

For reactions involving rate-determining hydroxide attack, the calculated second-order rate constants in micelles of ctab and ctas are similar and much less than those for reaction in water. For reactions involving rate-determining C-N bond breaking the calculated second-order rate constants in micelles of ctab are greater than in micelles of ctas, and similar to those for reaction in water.