Synthesis, Characterization, and Evaluation of Surface Properties of Cyclohexyloxyoxoethylbipyridinium Gemini Amphiphiles, and a Comparison with Single-Tailed Amphiphiles

Cyclohexyloxyoxoethylbipyridinium gemini amphiphiles have been synthesized in a two-step methodology. In the first step, cyclohexanol was esterified with chloroacetic acid or bromoacetic acid to get cyclohexyl-2-chloro (or bromo) ethanoates (3a/3b). These esters in the second step were reacted with either 4,4'-bipyridine or 2,2'-bipyridine to get the respective bipyridinium salts. The structure of these amphiphiles has been established by infrared (IR) spectroscopy, nuclear magnetic resonance (NMR), and mass spectroscopy. The interfacial parameters like counterion binding (beta), maximum surface excess concentration (Gamma(max)), minimum area per molecule (A(min)) of gemini amphiphiles have been evaluated and compared with single-tailed amphiphiles. A comparison of the critical micelle concentration (CMC) value of these gemini amphiphiles with corresponding single-tailed amphiphiles indicates that the geminis have CMC values 10-fold less than that of the single-tailed amphiphiles. The corresponding hexafluorophosphate and tetrafluoroborate gemini amphiphiles were also prepared. The melting points of monomeric and gemini amphiphiles has also been compared.