Structure of micellar head-groups and the hydrolysis of phenyl chloroformate - The role of perchlorate ion

Spontaneous hydrolysis of phenyl chloroformate is inhibited by micelles, but inhibition by SDS (n-C12H25OSO3Na) micelles is much greater than inhibition by cationic or sulfobetaine micelles (n-C16H33NR3X: CTAX, CTEAX, CTBAX, R = Me, Et, Bu, respectively, X = Cl, Br, OMs; n-C14H29N+R2(CH2)(3)SO3-: SB3-14, SBP3-14, R = Me, Pr, respectively, and n-C14H29N+Me2(CH2)(n)SO3-: SB4-14, SB5-14, n = 4 and 5, respectively). - Inhibition by cationic micelles increases with increasing head-group bulk and affinity of the counterion for cationic micelles, while addition of NaClO4 to sulfobetaines inhibits reaction strongly. Values of k(obs) relative to reactivity in water, for cationic micelles, are 0.64 (CTACl) and 0.32 (CTBABr); sulfobetaines behave similarly, but the corresponding values for SDS and sulfobetaine/ClO4- mixtures are ca. 0.06. These head-group and counterion effects indicate that depletion of water in the interfacial region complements the charge effect in controlling reactivity in micelles.