ACID-HYDROLYSIS OF P-METHOXYBENZALDEHYDE O-ACYLOXIME IN 1-BUTANOL-MODIFIED MICELLES OF SODIUM DODECYL-SULFATE

Rates of acid hydrolyses of p-methoxybenzaldehyde 0-acyloximes (p-MeOC 6H4HC=NOCOR, AMB and OMB, R = CH3 and n-C7H15, respectively) in micell es of 0.05 M sodium dodecyl sulfate (SDS) with 0.05-0.8 M HCI are redu ced by 1-butanol (BuOH). Reaction in aqueous HCI is slightly slowed by BuOH. Several factors contribute to the inhibition by BuOH in SDS mic elles: (i) BuOH reduces the transfer of H+ and AMB from the aqueous to the micellar pseudophase, but OMB is essentially fully micellar-bound ; (ii) BuOH increases the volume of the reaction region in the micella r pseudophase and decreases reactant concentrations in that region. In dilute HCI, competition between H+ and Na+ and the overall kinetics f it the pseudophase ion-exchange equation (PIE) and second-order rate c onstants in the micellar pseudophase are similar to those of AMB in Bu OH-H2O mixtures. In moderately concentrated HCI, e.g., 0.5 and 0.7 M, the PIE treatment underpredicts the concentration of H+ at the micella r surface and the overall rate constants. Modifications of the PIE whi ch allow for an increase in the concentration of H+ at the micellar su rface with an increase in the total [HCl] fit the data. In one treatme nt the local concentration of H+ at the micellar surface is assumed to increase linearly with [HCl]; in another it follows equations of the form of Langmuir isotherms. The treatments are compared.