Micellar effects upon the reaction of betaine esters with hydroxide ion

The reaction of hydroxide ion with methyl N,N,N-trimethylglycinate (1a) is inhibited by cationic micelles of C₁₄H₂₉NMe₃Cl and C₁₆H₃₃NMe₃Cl (MTACl and CTACl) because the substrate is largely in the aqueous pseudophase which is depleted in OH^- by the cationic micelles. Added Cl^- displaces OH^- from the micelles and decreases micellar inhibition. The corresponding reaction of methyl N-dodecyl-N,N-dimethylglycinate (1b) is catalyzed by both MTACl and CTACl which bind both reactants, but this catalysis is reduced by NaCl. Self-micellization of methyl N-hexadecyl-N,N-dimethylglycinate (1c) speeds reactions with OH^-, and the rate constants reach plateau values with increasing substrate concentration and are independent of OH^-. But addition of either CTACl or NaCl slows reaction because Cl^- displaces OH^- from the micelle. These diverse rate effects can be accounted for quantitatively in terms of the pseudophase ion-exchange model, which considers reactions in both the aqueous and micellar pseudophases and the distribution of both reactants between the pseudophases.