Micellar Charge Effects upon Hydrolyses of Substituted Benzoyl Chlorides. Their Relation to Mechanism

Abstract

Micellar rate effects on hydrolyses of substituted benzoyl chlorides, 1, depend on headgroup charge and electron donation or withdrawal by substituents. Micellized sodium dodecyl sulfate, SDS, inhibits hydrolyses, and first-order rate constants in the micellar pseudophase, k‘M, decrease, relative to those in water, k‘W, over a range of ca. 10, but in cetyl trimethylammonium chloride, CTACl, k‘M/k‘W > 1 for hydrolyses of 1,3,5-(NO2)2 and 1, 4-NO2, and decreases steeply with electron-donating substituents in the following sequence: 1,4-Cl ≈ 4-Br > 4-H > 4-Me > 4-OMe, over a range of >103. Cetyl trimethylammonium bromide and mesylate behave like CTACl. Fits to the Hammett equation give ρ ≈ 1 in SDS and ρ ≈ 4 in CTACl. Anionic micelles have higher interfacial polarities than cationic micelles, but micellar and solvent effects do not correspond because over a range of solvents, H2O to H2O−MeCN, 1:1 w/w plots of log k‘W against σ go through minima with positive ρ for 1, 3,5-(NO2)2, and 4-NO2 and negative for t...