HPMC effect on catalyzed hydrolysis of α-naphthyl acetate in cationic micellar systems

Abstract

Micelle formation is an important property of surfactants. Micellar solutions of cetyltrimethylamonium bromide (CTAB) have been found to accelerate the hydrolysis of α-naphthyl acetate (α-NA) by o-iodosobenzoic acid (IBA), a strong nucleophile. Critical micelle concentration (CMC) of CTAB was determined in the absence and presence of various concentrations and grades of hydroxypropylmethyl cellulose (HPMC) using surface tension measurement. Reaction under pseudo-first-order condition was utilized for rate constant determination. The aggregation of CTAB in the polymer solution started at higher concentration than in the absence of the polymer. The observed rate constants for the degradation of α-NA in the presence of various concentrations of CTAB with and without HPMC were calculated. The presence of HPMC retarded the reaction rate. However, there was no obvious difference in the observed rate constant among the different grades of HPMC (Methocel E50 ®, Methocel E4M ®, Methocel E10M ®) while the higher the polymer concentration the lower the rate constant.