Oxidation of butane-1,3-, butane-1,4-, 2-methyl pentane-2,4- and 3-methyl pentane-2,4-diols by cerium(IV) in aqueous acidic medium catalyzed by rhodium(III)

The oxidation kinetics of butane-1,3-diol, butane-1,4-diol, 2-methyl pentane-2,4-diol and 3-methyl pentane-2,4-diol with cerium(IV) catalyzed by rhodium(III) in aqueous sulfuric acid showed a peculiar nature with respect to the variation in oxidant concentration, such that the reaction follows first-order kinetics in Ce(IV)] at low Ce(IV)] and then reaches a maximum with increasing Ce(IV)], beyond which further increase in the oxidant concentration retards the rate. The rate shows direct proportionality with respect to diol] at low concentrations, becoming independent of diol] at higher concentrations. The rate is first order in catalyst. Retarding effects are observed when H⁺] and Ce(III)] are increased, while Cl⁻] and hence ionic strength have a positive effect on the rate. Spectroscopic studies confirmed that the primary hydroxyl groups in butane-1,3-diol and butane-1,4-diol resulted in the formation of 3-hydroxy butanal and 4-hydroxy butanal, respectively. In the case of oxidation of the secondary hydroxyl groups in 2-methyl pentane-2,4-diol and 3-methyl pentane-2,4-diol, the products of oxidation were 4-hydroxy-4-methyl pentan-2-one and 4-hydroxy-3-methyl pentan-2-one, respectively.