SECONDARY VALENCE FORCE CATALYSIS .9. CATALYSIS OF HYDROLYSIS OF PARA-SUBSTITUTED BENZALDEHYDE DIETHYL ACETALS BY SODIUM DODECYL SULFATE

The acidic hydrolysis of substituted benzaldehyde diethyl acetals is subject to catalysis by dilute aqueous solutions of sodium dodecyl sulfate. Second-order rate constants for these reactions are independent of surfactant concentration below the critical micelle concentration, then increase rapidly with increasing surfactant concentration, level off, and finally decrease slightly with further increases. Second-order rate constants for the reactions in aqueous solution and in the presence of optimal concentrations of the surfactant are well correlated by Hammett σ constants. Values of ρ of -3.3 and -4.1 were obtained for the purely aqueous medium and the surfactant solutions, respectively. Thus, catalysis of hydrolysis of benzaldehyde diethyl acetals by sodium dodecyl sulfate is more important for those substrates possessing electron-donating substituents than for those possessing electron-withdrawing substituents. The maximum rate increase observed with the p-nitro substrate is only 17-fold while that observed with the p-methoxy substrate is 146-fold.