Micellar Effects upon the Reaction of Betaine Esters with Hydroxide Ion

Article abstract of DOI:10.1021/j150614a034

The reaction of hydroxide ion with methyl N,N,N-trimethylglycinate (1a) is inhibited by cationic micelles of C14H29NMe3Cl and C16H33NMe3Cl (MTACl and CTACl) besause 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 reaction 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 effents 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.