Micellar effects on the reduction of <i>p</i>-nitroso-N,N-dimethylaniline by sulphite ions

Abstract

Micellar effects on the rate of reduction of <i>p</i>-nitroso-N,N-dimethylaniline by sulphite ions in a buffer medium of <i>p</i>H 6.5 have been investigated. A nonionic surfactant, polyoxyethylene (23) dodecanol (Brij-35, 1 x 10^-² <i>M</i>), catalyses the reaction and increases the rate by 34 times whereas the same concentration of a cationic surfactant cetyltrimethylammonium bromide (CTAB) catalyses the reduction by 11 times. Anionic surfactant sodium dodecyl sulphate (SDS) has little effect on the reduction rate. Catalytic effects have been attributed to the hydrophobic and electrostatic interactions between the substrate, reductant and micelles. Micelle-substrate binding constants have been found to be 470 and 759 <i>M^-1 </i> for CTAB and Brij-35 catalysed reactions respectively. Influence of micelles on the activation parameters of the reaction has been discussed.