Influence of the addition of alcohol on the reaction methyl-4-nitrobenzenesulfonate + Br − in tetradecyltrimethylammonium bromide aqueous micellar solutions

Abstract

The reaction methyl-4-nitrobenzenesulfonate + Br − was studied in tetradecyltrimethylammonium bromide (TTAB) aqueous micellar solutions in the absence and in the presence of various amounts of n-hexanol, n-pentanol, and n-butanol. Kinetic micellar effects provoked by the addition of the linear alcohols can be rationalized by using simple pseudophase kinetic models. The equilibrium binding constants of the methyl-4-nitrobenzenesulfonate molecules to the cationic micelles decreases when [alcohol] increases. The ( k 2 m / V m ) values found are practically the same for the different TTAB–alcohol micellar solutions studied, independent of the nature and concentration of the alcohol present in the reaction medium. This has been explained by considering the balance of two factors operating on reactivity in opposite ways: (1) an increase in the volume of the micellar interfacial region upon increasing alcohol concentration, and (2) a decrease in the polarity of the interfacial region as the amount of alcohol present in the micellar solutions increases.