Synthesis and surfactant properties of symmetric and unsymmetric sulfosuccinic diesters, Aerosol-OT homologues

The synthesis and surfactant behaviour of two series of sulfosuccinic diesters, AOT-related compounds, are described [Aerosol-OT 1: sodium bis(2-ethylhexyl) sulfosuccinate]. The first family contains unsaturated, racemic or enantiopure, 2-ethylhex(en)yl chains with various positions of the double bond. These compounds are readily prepared from the corresponding unsaturated alcohol by the standard two-step procedure; their critical micelle concentrations are higher than those of normal AOT and depend on the position of the double bond. The second series consists of nonsymmetric homologues with two different substituents: various unsymmetrical sulfosuccinic diesters with two enantiopure saturated or unsaturated chains of opposite configuration, or with two different substituents like methyl and 2-ethylhexyl, hydrogenated and deuterated chains as well as saturated and unsaturated chains are described. These unsymmetrical sulfosuccinic diesters are readily obtained in a three-step synthetic procedure involving the regiospecific sulfonation of maleic monoester in aqueous medium. The structure of the sodium 4-alkyl-2-sulfosuccinic acid key intermediate is unambiguously resolved by NMR comparative analysis of the hydrogenated and deuterated derivatives. The surfactant behaviour of some unsymmetrical compounds is studied.