Effects of anionic micelles on the intramolecular general-base-catalysed hydrazinolysis and hydrolysis of phenyl salicylate. Evidence for a porous cluster micelle

Abstract

The hydrazinolysis of phenyl salicylate has been studied in the presence and absence of micelles of sodium dodecyl sulphate (SDS) at 30 °C. The nucleophilic reaction of hydrazine with ionized phenyl salicylate (PS–) involves intramolecular general-base catalysis while the probable intramolecular general-acid catalysis could not be detected in the reaction of non-ionized phenyl salicylate (PSH) with hydrazine. Kinetic data for both hydrolysis and hydrazinolysis of phenyl salicylate are explained in terms of the pseudophase model of micelles. The rate constants for hydrolysis and hydrazinolysis of PS– in micellar pseudophase are either insignificant or significantly smaller compared with the corresponding rate constants in aqueous pseudophase. This is attributed largely to considerably low water activity in the specific micellar environment where micellar bound PS– molecules exist. The micellar bound reactants (PSH and PS–) and products (non-ionized and ionized phenol and N-hydrazinylsalicylamide) appear to exist in the micellar environments of different water activity. The rate constants, Kobs′ increase ca. fivefold with increased [NaOH] from 0.001 to 0.040 mol dm–3 at 0.2 mol dm–3 SDS and 0.08 mol dm–3 NH2NH2. This is attributed to an increase in [PS–] with increase in [NaOH]. These observations favour the porous cluster micellar structure. The values of Kobs remain unchanged with increased concentration of 1,4-diazabicyclo[2.2.2]octane from 0.06 to 0.60 mol dm–3 at 0.3 mol dm–3 SDS, 0.05 mol dm–3 NaOH, and 37 °C. This shows that the presence of SDS micelles does not change the reaction mechanism of aqueous pseudophase hydrolysis and aminolysis of PS–.