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The effect of the different binary aqueous organic solvents viz. 1,4-dioxane, acetonitrile, dimethylsulfoxide, ethylene glycol, and methanol, on the micelle formation and thermodynamics of a cationic surfactant cetyl triphenyl phosphonium bromide has been studied conductometrically at 298-318 K. From the conductivity data critical micelle concentration, degree of counter ion dissociation (a) and thermodynamic parameters of micellization have been determined. It is observed that micellization tendency of the surfactant decreases in the presence of binary aqueous solvents. The entropies of micellization are all positive, and they compensate the enthalpies of the process.

Nucleophilic substitution reaction of p‐nitrophenyl acetate (PNPA), p‐nitrophenyldiphenyl phosphinate, and pesticide parathion with different α‐nucleophiles [I] have been studied at 27 °C in different pH in the presence of a novel cationic surfactant. The kinetic study was performed spectrophotometrically under pseudo‐first order conditions with the α‐nucleophile in excess. The pKa of nucleophiles have also been determined by kinetic method. In the presence of surfactant, the rate constant increased with increasing surfactant concentration up to a limiting value. This behavior has been analyzed in quantitative terms on the basis of pseudo‐phase model of micellar catalysis. Finally the nucleophilic reactivity of hydroxamate ions has been compared with other α‐nucleophiles, like oxime, hydroxybenzotriazole, and 2‐iodosobenzoic acid (IBA). The order of cleavage of electrophilic centers, that is, CO, PO, and PS have also been discussed. Copyright © 2008 John Wiley & Sons, Ltd.

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