Catalytic Effect of Cationic Gemini Micelles on the Rate of Condensation between Glycyl-DL-Aspartic Acid and Ninhydrin in the Absence and Presence of Organic Solvents

The reaction between glycyl-dl-aspartic acid (Gly-dl-Asp) and ninhydrin has been investigated in cationic gemini surfactants [alkanediyl-alpha,omega-bis (dimethyltetradecylammonium bromide)] (14-m-14). The study was carried out as functions of [Gly-dl-Asp], [ninhydrin], solvent (v/v %) and [surfactant] at pH = 5.0 and 70 A degrees C. The reaction followed first-order kinetics in [Gly-dl-Asp] and fractional-order kinetics in [ninhydrin]. The reaction is catalyzed by TTABr/14-m-14. Addition of an organic solvent at fixed [surfactant] increases the absorbance as well as the rate of formation of Ruhemann's purple. The results obtained in micellar media are treated quantitatively in terms of pseudophase and Piszkiewicz kinetic models. The Eyring equation is valid for the reaction over the range of temperatures used and different activation parameters have been evaluated. The kinetic data have been used to calculate the micellar binding constants K (S) for Gly-dl-Asp and K (N) for ninhydrin.