Kinetics and mechanism of the oxidation of some alpha-hydroxy acids by tetrachloroaurate(III) in acetic acid-sodium acetate buffer medium

The kinetics of oxidation of some neutralized alpha-hydroxy compounds such as glycolic (CA), lactic (LA), alpha-hydroxyisobutyric(IB), mandelic (MA) a trolactic (AL), and benzilic (BA) acids by tetrachloroaurate(III) have been studied. The substrates are oxidized to give formaldehyde, acetaldehyde, a cetone, benzaldehyde, acetophenone, and benzophenone for the respective rea ctions. The rate of the reaction increases with increasing [substrate] and pH but decreases with increase in [Cl-]. Temperature influence is quite mar ked in ail these reactions. A mechanism involving the formation of an unsta ble complex, which decomposes to give the respective reaction products, is proposed. The reactivity of the alpha-hydroxy acids towards gold(III) are a s follows: AL > MA >. BA > IB > LA > GA. (C) 1999 John Wiley & Sons, Inc.