Synthesis and Surface Active Properties of Long Chain Alkylthiobetaines

Abstract

Long chain alkylthiobetaines, CnH2n+1S+ (CH3) CH2COO-, where n is 10, 11, 12, 14, or 16, were synthesized and their zwitterionic structures were confirmed by IR and NMR spectra in aqueous solutions. The critical micelle concentrations (cmc) were determined by surface tension and light scattering method and they were in good agreement with each other. The relations between the logarithm of cmc and the number (n) of carbon atoms in the alkyl chain were as follows;log cmc=3.27-0.50n by surface tension method at 30°Clog cmc=3.53-0.52n by light scattering method at 21°COn the other hand, a linear relationship was found between the logarithm of the aggregation number (m) of micelles and the alkyl chain length. It was expressed as follows; log m=0.14n+0.29 (n=1012) These results were discussed by comparison with other amphoteric surfactants such as N-alkylbetaine and N-alkylsulfobetaine.