Abstract
We have examined micelle formation of a long chain alkyl quaternary ammonium salt with a ferrocenyl group introduced at the end of the hydrophobic chain, (11-ferrocenyl) undecyltrimethylammonium bromide (FTMA), and the effect-of oxidation of the ferrocenyl group on the solubilization of benzene derivatives by FTMA micelles.
Determinations of the critical micelle concentration (cmc) of FTMA by the surface tension method revealed that the reduced form (FTMA+) has a cmc value of 7 x 10-5 mol/L while the oxidized form (FTMA2+) exhibits its cmc at 1 x 10-3 mol/L, about 15 times higher than that for the reduced form. At 50% oxidation of FTMA+, the cmc was 6 x 10-4 mol/L, an intermediary value of those for FTMA+ and FTMA2+. The changes in cmc caused by the oxidation were confirmed by electroconductivity measurements, thus demonstrating that the cmc shifts towards the higher concentration side with proceeding oxidation of the ferrocenyl group.
Investigations were then made of the solubilization in aqueous FTMA solutions of three benzene derivatives with different solubilities in water, ethylbenzene (EtBz), 2-phenylethylalcohol (PEA), and benzyl acetate (BA). The maximum amount solubilized was found to decrease for all solutes with progressive oxidation of FTMA. Similarly, a decrease was also found in the number of moles of solute per mole of surfactant constituting micelles (solubilizing capacity) with rising degree of oxidation. This was ascribed to a decrease not only in the number of FTMA molecules forming micelles but also in the number of sites of the solubilization in micelles as the oxidation proceeded. Examination of the effect of oxidation of the ferrocenyl group on the solubilization equilibrium constant of solute showed that FTMA oxidation makes it difficult for all three aromatic compounds to be solubilized.
