QUANTITATIVE TREATMENT OF KETAL HYDROLYSIS IN AQUEOUS-SOLUTIONS CONTAINING POLYMER SURFACTANT COMPLEXES USING A PSEUDOPHASE KINETIC-MODEL

The acid-catalyzed hydrolysis of 2-(p-methoxyphenyl)-1,3-dioxolane and benzaldehyde di-tert-butyl acetal has been studied in the presence an d absence of poly(ethylene oxide)-sodium dodecyl sulfate (PEO-SDS) sol utions. The kinetic data were interpreted in light of the pseudophase ion-exchange (PPIE) formalism by assuming that reaction can occur in t hree pseudophases, namely, aqueous, micellar, and PEO-SDS complex. The degree of ionization (a) for PEO-SDS complexes was determined from th e ratio of the slopes of conductivity against [SDS] above and below th e critical aggregation concentration (cac) by the application of Evans equation. Values of 0.25 and 0.41 for SDS micelles and PEO-SDS comple xes, respectively, were found. Free micelles are shown to be better ca talysts than PEO-SDS complexes because of (i) the lower a value of fre e micelles and because (ii) second-order rate constants for the acid h ydrolysis reactions in SDS micelles are higher than in PEO-SDS complex es.