Ion-pair aggregation of a long-chain carboxylic acid and an amine in benzene studied by induced circular dichroism

Abstract

Association of the ion-pairs from 2-(4-alkylbenzoyl)benzoic acids and (–)-(R)-amphetamine or (+)-(R)-N-cetyl-α-phenylethylamine in benzene was investigated by i.c.d. In non-polar solvents, such as benzene and carbon tetrachloride, the ion-pairs of (–)-(R)-amphetamine and (+)-(R)-N-cetyl-α-phenylethylamine with 2-(4-alkylbenzoyl)benzoic acids where the alkyl group consists of a hydrocarbon chain with more than six carbon atoms, exhibited association phenomena in solutions of salt concentrations <10^–3M; these produced large increases in the magnitude of the i.c.d. effect. Aggregation did not occur in relatively polar solvents such as tetrahydrofuran, acetonitrile, and methanol. The aggregates are assumed to be spherical micelles with the polar groups in the core thus giving polar space. The core of the micelles containing (+)-(R)-N-cetyl-α-phenylethylamine is a large asymmetric space which results in the large i.c.d. on the chromophore of the guest molecule.