Reactivity in Quaternary Water in Oil Microemulsions. 2. Different Distribution of the Reagents Changing from Three- to Four-Component Microemulsions

Abstract

A study was carried out on the nitrosation of piperazine (PIP) and N-methylbenzylamine (MeBzAm) by N-methyl-N-nitroso-p-toluenesulfonamide (MNTS) at 25 °C in quaternary tetradecyltrimethylammonium bromide (TTABr)/1-hexanol/isooctane/water microemulsions, ensuring that the relationship [1-hexanol]/[TTABr] = 4 remained constant. In order to interpret the experimental results, we extended the formalism of the micellar pseudophase to microemulsions thereby considering the distribution of the alcohol throughout the pseudophases of the microemulsion and the change in the volume of the interface. The volume of the interface, calculated from the molar volumes of the surfactant and the alcohol, was included in the kinetic model to quantify the dilution of the reagents associated at the interface. The application of the developed kinetic model to the two systems studied has shown that the presence of alcohol in the continuous medium increases its hydrophilicity. Hence, unlike in the case of the tertiary AOT/isooctane/water microemulsions, it is necessary to bear in mind that the piperazine is distributed between the three pseudophases of the microemulsion. A comparison of the results obtained in TTABr/1-hexanol/isooctane/water microemulsions with those of AOT/isooctane/water shows that the incorporation of the alcohol into the interface increases its hydrophobicity by displacing water molecules and hence reducing the bimolecular rate constant for the reaction at the interface.