SYNTHESIS AND PROPERTIES OF PIPERAZINE DERIVATIVES AND THEIR QUATERNARY AMMONIUM AMPHIPHILIC SALTS

A series of long-chain piperazine derivatives, N-alkyl-N'-methyl piper azine and their amphiphilic salts, N-alkyl-N'-ethyl-N'-methyl piperazi nium bromide, and the related N-alkyl-N,N'-dimethyl piperazinium bromi de were synthesized and characterized by H-1 and C-13 NMR and FTIR spe ctroscopy. Under the experimental conditions used, the NMR data showed unequivocally that quaternarization of N-alkyl-N'-methyl piperazine b y the reaction with ethyl bromide occurred exclusively at the nitrogen atom bearing the methyl group due to the steric hindrance of the long -chain alkyl group attached to the other nitrogen atom. Critical micel le concentration (cmc) and surface-active properties of the amphiphile s were investigated. Plots of surface tension, gamma, against log conc entration were presented. At cmc, the number of molecules adsorbed at the air-water interface was found to decrease with increasing chain le ngth. This was attributed to the increase in electrostatic repulsion w ithin the adsorption layer as suggested by Lunkenheimer et al. (Colloi ds Surf. A 101, 197 (1995)). (C) 1996 Academic Press, Inc.