Hydroxy-ketones a-ketols, acyloins

The oxidation of acetoin by Fe(ni) perchlorate follows the stoichiometry 2Fe(rrr)+CH3COCH(OH)CH3 = 2Fe(f[)+CH3COCOCH3+2H and the rate law 

The two terms correspond to oxidation by Fe and Fe(OH) which exist in a hydrolytic equilibrium. A radical intermediate CH3COC(OH)CH3, which suffers rapid oxidation by a second ferric ion, is proposed. 

Ferricenium ion oxidation of acetoin in acidic aqueous ethanol (50 % v/v) involves rate-determining enolisation , producing a zero-order decay of oxidant. The oxidation rate approximates to that of deuteration under similar conditions. 

Several studies have been made of oxidations of ketols by Cu(II). Simple cupric salts deposit cuprous oxide, but this has been overcome by using a citrate complex of Cu(II) or a 1 1 (mole) pyridine-water mixture. A recent detailed account is that of Wiberg and Nigh ° , who found the stoichiometry and rate law for the oxidation of a-hydroxyacetophenone by Cu(II) acetate to be, respectively, 

The first term was found to correspond to the rate of enolisation (measured by an NMR study of hydrogen-deuterium exchange at the methylene group). The second term predominates at [Cu(II)] 10 M and is characterised by a primary kinetic isotope effect of 7.4 (25 °C) and a p value of 1.24. Addition of 2,2 -bipridyl (bipy) caused an increase in 2 up to a bipy Cu(II) ratio of 1 1 but at ratios greater than this 2 fell gradually until the enolisation term dominated. The oxidation of a-methoxyacetophenone is much slower but gives a similar rate 

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