Effect of CHAPS and CPC micelles on Ir(III) catalyzed Ce(IV) oxidation of aliphatic alcohols at room temperature and pressure

Abstract

Kinetics of cerium(IV) oxidation of aliphatic alcohols: ethanol, propanol, propan-2-ol, 1-butanol and 2-butanol were studied at 30°C in the presence and absence of surfactants in acidic medium. The reaction was studied under pseudo-first-order conditions, [alcohol]T≫[Ce(IV)]T. Ir(III)-salt used as catalyst had a significant effect on reaction rate. Cationic surfactant CPC (N-cetylpyridinium chloride) inhibits the reaction rate but zwitterionic surfactant CHAPS (3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate) catalyzes the oxidation reaction significantly. CMC value of CHAPS was determined by a spectrofluorometer. The reaction rate increased with increase in the acid concentration of the medium. NMR and FTIR spectra confirmed the oxidized products. The aggregation of surfactants in the reaction condition was studied through Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM). Dynamic light scattering (DLS) was used to characterize the shape changes of the aggregates. The variations of the reaction rates for the different alcohols in the presence of surfactants and metal ion catalyst are discussed qualitatively in terms of Berezin's model, nature of surfactants, and charge of surfactants. Ir(III) in association with CHAPS micellar catalyst exhibited ~500–2000fold rate enhancements compared to the uncatalyzed reaction path.