Oxidation of 1,2-hydroxyketones

Only one kinetic study has been reported. The oxidation of 3-hydroxy-3-methyl-butane-2-one is second-order with a rate maximum at pH 8 (Bunton and Shiner ). The same authors carried out an experiment at pH 8 which shows that the C-OH bond is not broken, as in the oxidation of 1,2-diols. The mode of attack on the carbonyl group is probably nucleophilic at the carbon atom, as in the oxidation of 1,2-diketones. 

Phenol itself is only oxidised slowly by periodate (Adler and Magnusson ) but many substituted phenols are oxidised rapidly. Sklarz has reviewed the extensive work done on the stoichiometry of the oxidations of the latter. Few kinetic studies have been carried out. Kaiser and Weidman found second-order kinetics (first with respect to each reactant) for the oxidation of quinol and its monomethyl ether at 15° and 25 °C, i.e. 

Increase of pH in the range 0-4 decreases the rate. The pH dependence can be accounted for quantitatively by assuming different reactivities for HsIOg and a periodate monoanion. Kaiser and Weidman later studied the oxidation of catechol using a stopped-flow apparatus, and showed that the reaction proceeded via an intermediate. The formation of the latter was second order, and at pH 1.0 the second-order rate coefficient is expressed by (from measurements at 15° and 25 °C) 

The activation parameters are similar to those for the overall reactions of quinol and its monomethyl ether (above). The pH dependence of 2 shows a gradual increase in the range pH 1-4, then a more rapid increase to a maximum at pH 8.5, followed by a rapid decrease. Kaiser and Weidman accounted for this quantitatively by assuming reactions of catechol with HsIOg and a periodate monoanion, and either reaction of catechol with or reaction of the 

The decomposition of the intermediate in the catechol oxidation is first-order and is subject to catalysis by hydrogen ions, viz. 

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