Synthesis and evaluation of new imidazolium‐based aromatic ether functionalized cationic mono and gemini surfactants

Abstract

Synthesis of a novel series of imidazolium-based surfactants, [(ROArCH2MIm)Br] with aromatic ether functionalized hydrophobic tail of varying chain lengths and also their gemini counterparts were conducted in the present work. Synthesis involves initial conversion of 4-hydroxy benzoic acid to its methyl ester followed by its O-alkylation with long chain fatty alcohols, which was subsequently reduced and brominated to get 4-alkyloxy benzyl bromide. For the synthesis of monocationic surfactant, 4-alkyloxy benzyl bromide is quaternized with N-methylimidazole. Gemini surfactants are synthesized by initial coupling of imidazole to 4-alkyloxy benzyl bromide followed by its quaternization with dibromoalkane. The surface properties of all the synthesized surfactants were determined using surface tensiometry. Within the same homologous series, expected decrease in critical micelle concentration (cmc) with the increase in hydrophobicity was observed for shorter chain homologs. However, the deviation in cmc value from regularity was observed when the number of carbon atoms in the hydrophobic chain exceeded a certain number. The cmc values of the geminis were found to be remarkably low compared to their monomeric counterparts.