Water-Catalyzed Hydrolysis of 1-Acyl-1,2,4-triazoles in the Presence of Surfactant-Polymer Mixed Micelles. Substrate Dependence of the Effect of Polymer on the Micellar Inhibition

Article abstract of DOI:10.1021/jo00201a010

The water-catalyzed hydrolysis of 1-benzoyl-1,2,4-triazole (1) is inhibited by SDS micelles.Addition of poly(vinylalcohol)-poly(vinyl acetate) copolymers (17percent and 26percent acetate, respectively) leads to a decreased inhibition.As supported by conductivity measurements, the rate effects are attributed to the formation of SDS-copolymer mixed micelles.Ultrafiltration experiments indicate increased binding of the substrate to the mixed micelles.Therefore the copolymer-induced rate accelerations can be best reconciled with an increase in the micropolarity at the substrate binding sites in the mixed micelles relative to unperturbed SDS micelles.With the aid of a computer, all kinetic data can be fitted into a kinetic scheme assuming hydrolysis of 1 in bulk water and in SDS and SDS-copolymer micellar pseudophases.Hydrolysis in SDS-poly(N-vinylpyrrolidone) (PVP) mixed micelles at low SDS concentrations (3-10 mM) was studied with the more hydrophobic substrate 3-phenyl-1-benzoyl-1,2,4-triazole (3).Now the SDS-induced inhibition is further increased by the polymer.Kinetic analysis shows that 3 is less strongly bound to mixed SDS-PVP micelles than to SDS micelles but that the rate constants in both micellar pseudophases are rather similar.It is argued that the different behavior of 1 and 3 in the mixed micelles primarily reflects the large propensity of 3 for stabilization by hydrophobic interactions.