Chromic Acid Oxidation of Lactic Acid Catalysed by Manganese(II)

B ak o re and N a r a in 1 studied the kinetics of the oxidation of a-hydroxy acids by chromium(VI) and found that addition of Mn(II) decreases the rate of oxidation to one half of that in absence of Mn(II), when the hydrogen ion concentration is in the range 0.1 to 0.4 M. They attributed this to the disproportionation of Cr(IV) by Mn(II) ions. K em p and W a t e r s 2 observed Mn(II) catalysis in the oxidation of a-hydroxy isobutyric acid by Cr(VI), when concentration of sulphuric acid exceeds 1.0 M. Recently S u n d a r a m and V e n k a t a su b r a m a n ia n 3 reported Mn(II) catalysis in chromic acid oxidation of hydroxy acids. Unfortunately they have not mentioned the pH range in which they have observed the catalysis and this prevents verification of their conclusions. In view of the conflicting reports, it was considered desirable to investigate the role of Mn(II) in the oxidation of a-hydroxy acids by Cr(VT) under well defined conditions of acidity. The present report deals with the effect of Mn(II) in the oxidation of lactic acid by chromium (VI).