The Effects of Inorganic Salts and Urea on the Miceliar Structure of Nonionic Surfactant using Keto-enol Tautomerisrn of Benzoylacetanilide

Abstract

It is known that the tautomerism of benzoylacetanilide (BZAA) shifts to the ketonic form in aqueous phase, but lies on the enolic form in nonaqueous media or in the micelle of sur-factant. This phenomenon can be used to study the effects of inorganic salts and urea on the mode of packing of the micelle of nonionic surfactants. The increase in the packing of sur-factant molecules in the micelle makes the inside of the micelle behave like a nonpolar solvent and causes an enhancement in the intensity of absorption spectra of the enolic form. Using the keto-enol tautomerism of BZAA, it was shown that the micelle of a homogeneous hepta- ethylene glycol dodecl ether (7 ED) increased in the compactness with the addition of KNO₃, KBr, KC1, and K₂, SO₄, and decreased with the addition of KSCN and urea. Furthermore, the change in the cloud point of 7 ED by the addition of salts and urea was found to corres-pond fairly well to the degree of enolization, consequently to the change in the packing of 7 ED monomers in the micelle. These results coincided with those obtained by the charge-transfer interaction between the nonionic surfactant and 7, 7, 8, 8-tetracyanoquinodimethane in a solubilized system.