Analysis of cationic and amphoteric surfactants: III. Structural analysis of imidazolinium cationic surfactants

Determination of the homologous distribution of imidazolinium cationic surfactants and their structural analysis have been inves-tigated. These surfactants were hydrolyzed under aqueous alkaline media, followed by acid hydrolysis to afford fatty acids and poly-amines. The resulting fatty acids were esterified with methanol, and then analyzed by gas chromatography (GC) in order to determine their homologous distribution. The obtained distribution agrees well with that of original fatty acid. Therefore, this method should be applicable to the determination of the homologous distribution of imidazolinium surfactants. The resulting polyamines were acetylated with acetic anhydride in the presence of pyridine. These acetates were analyzed by GC and isolated by preparative thin layer chroma-tography on silica gel. The structures of these isolates were identi-fied by means of 1 H-NMR and 1R spectrometry. These structural analyses demonstrated that quaternization of an imidazoline ring selectively occurred at the nitrogen at the 3-position of an imida-zoline ring, which was the kinetically favored position in terms of the steric hinderence and the stability of product.