The kinetics of oxidation of benzylic acid (HLH) to benzophenone by cerium (IV) has been studied in several media using the stopped-flow technique. In HClO4-Na2SO4-NaClO4 media, which allow for the variation and control of the concentrations of the various Ce(IV) species at constant [H+] and ionic strength, the rate data suggest CeSO42+ as the kinetically relevant species. In HClO4 the observed first-order rate constants, tetrad, first increase with increasing HLH concentration, then decrease slightly at higher substrate concentrations suggesting the intermediacy of two complexes: a reactive [Ce(IV)HL] and a [Ce(IV)(HL)2] which resists reaction. The rate law which best describes the observed kinetics in HClO4 media is given by [formula ommitted] where K7 ′ and K8′ are H+-dependent equilibrium constants for the formation of the 1:1 and 1:2 complexes, respectively. The kinetic parameters kα and kβ are the rate constants for the intramolecular redox reaction of the 1:1 and 1:2 complexes, respectively. The rates in H2SO4 are much slower than those in HClO4 and do not reflect strong complex formation before electron transfer. Whereas H+ had an inhibiting effect in the above-mentioned media, catalysis by H+ was manifest in HClO4-HOAc media, possibly through decreasing acetato complexation of Ce(IV). © 1977, American Chemical Society. All rights reserved.



International Standard Serial Number (ISSN)

1520-6904; 0022-3263

Document Type

Article - Journal

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© 2023 American Chemical Society, All rights reserved.

Publication Date

01 Jun 1977

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