Micellar Catalysis and Product Stabilization in Hydrazone Formation Reactions and Micellar-Modified Determination of Hydrazine and Phenylhydrazine
摘要:
Kinetics and equilibria of condensation reactions of hydrazine and phenylhydrazine with p-(dimethylamino)benzaldehyde in micellar sodium dodecyl sulfate solutions were studied spectrophotometrically. The reaction with hydrazine involves consecutive reversible addition of two aldehyde molecules. The reaction rate under conditions of high excess of aldehyde is determined by the acid-catalyzed attack of aldehyde by hydrazinium cation. The reaction with phenylhydrazine proceeds slower and is characterized by a much smaller equilibrium constant as compared to the reaction with hydrazine. Micelles strongly enhance the observed rate (ca. 10(2) times) and equilibrium (ca. 10(4) times) constants of the reaction with hydrazine and exert more modest (20-30 times) enhancement of the respective parameters of the reaction with phenylhydrazine. The binding constants of reactants and reaction products to surfactant micelles as well as the intrinsic rate constants of the reactions in the micellar pseudophase were calculated from dependencies of observed rate constants and reaction yields on surfactant concentration. Spectrophotometric and kinetic methods of hydrazine determination based on its interaction with p-(dimethylamino)benzaldehyde in micellar medium are suggested, which avoid additions of concentrated acids and organic solvents, use ca. 100 times more diluted reagent solution, and can be performed in a shorter time as compared to the traditional procedure.