Homogeneous oxidation of alkanes: Role of rhodium–alkyl complexes

Abstract

Catalytic systems RhCl₃–KI–NaCl and RhCl₃–Cu(OAc_f)₂–NaCl in aqueous perfluorinated carboxylic acids (CF₃COOH, C₃F₇COOH) are effective in coupled oxidation of alkanes and carbon monoxide with dioxygen. In their presence, predominant is the outer-sphere oxidation of alkanes into respective esters (alcohols) with involvement of peroxo rhodium species as an oxidant (mechanism A). The process occurs partially by the inner-sphere mechanism B involving Rh–alkyl intermediates. Mechanism B is supported by (a) formation of alkyl chlorides, (b) synthesis of acetic acid in conversion of methane, and (c) positional selectivity in oxidation of propane.