Effects of nonionic, cationic, and mixed nonionic-cationic surfactants on the acid-base behavior of phenyl salicylate

The effects of Brij 35 micelles, CTABr micelles, and mixed Brij 35-CTABr micelles on the acid-base behavior of phenyl salicylate (PST) have been studied in aqueous solution containing 2% v/v acetonitrile, The apparent pK(b) (pK(b)(app)) of PST is decreased by 1.5 pK units with the increase in [Brij 35] from 0 to 0.02 M which is attributed to micellar medium effect. The values of pK(b)(app) remain almost independent of [CTABr] within its range 0.01-0.03 M. The increase in [CTABr] from 0 to 0.03 M in aqueous solution containing 0.02 M Brij 35 has not resulted in a change in pK(b)(app). This shows that the characeristic structural features of nonionic Brij 35 micelles remain essentially unchanged on addition of CTABr under the present experimental conditions. (C) 1999 Academic Press.