Original scientific paper

Spontaneous Hydrolyses in Sulfobetaine Micelles. Dependence of Micellar Charge Effects Upon Mechanism

Clifford A. Bunton ; Department of Chemistry and Biochemistry, Universitj of California, Santa Barbara, California, 93106, USA
Nicholas D. Gillitt ; Department of Chemistry and Biochemistry, Universitj of California, Santa Barbara, California, 93106, USA
Marutirao M. Mhala ; Department of Chemistry and Biochemistry, Universitj of California, Santa Barbara, California, 93106, USA
John R. Moffatt ; Department of Chemistry and Biochemistry, Universitj of California, Santa Barbara, California, 93106, USA

Abstract

Rate constants of spontaneous hydrolyses in zwitterionic micelles of N-hexadecyl-N,N-dimethyl-3-ammonio-propanesulfonate (SB3-16) are compared with those in cationic (n-C₁₆H₃₃NMe₃X, X = Cl, Br, OMes; CTAC1, CTABr, CTAOMes) and anionic (n-C₁₂H₂₅OSO₃Na, SDS) micelles. Substrates are methyl benzenesulfonate, 2-adamantyl and pinacolyl 4-nitrobenzenesulfonate, 4-bromo- and 4-nitrobenzoyl chloride, phenyl and 4-nitrophenyl chloroformate and bis(4-nitrophenyl) carbonate. Hydrolyses are micellar inhibited, except for the nitro substituted acid chlorides. Reactions with extensive bond-breaking in the transition state (S_N1 hydrolyses) are faster in SDS than in cationic and sulfobetaine micelles, but the other hydrolyses, which involve significant bond-making, are slower in SDS. Rate constants are similar in cationic and sulfobetaine micelles. These micellar charge effects are ascribed to interactions of the polar transition states with the asymetrically charged interfacial region which complement effects of the lower polarities of micelles relative to water.

Keywords

hydrolysis; deacylation; S_N1-S_N2 reactions; sulfonyl chlorides; surfactants; pseudophase treatments

Hrčak ID:

131862

URI

https://hrcak.srce.hr/131862

Publication date:

1.8.2001.

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