OXIDATION OF ALPHA-HYDROXYACIDS BY N-BROMOPHTHALIMIDE - DEPENDENCE OFMECHANISM ON PH OF THE MEDIUM

The oxidation of alpha-hydroxyacids, namely mandelic acid, lactic acid , malic acid, benzilic acid and atrolatic acid and N-bromophthalimide to give the corresponding carbonyl compounds, has been carried out. It was of interest to determine whether: the alcoholic OH or the carboxy lic OH is involved in the oxidative decarboxylation of alpha-hydroxy a cids which have bifunctional groups. A study of the dependence of rate on the pH of the medium was expected to differentiate between these t wo routes. Further, the alpha-hydroxyacids may react as simple alcohol s and undergo oxidation involving a C-H bond cleavage to give keto aci ds which may subsequently undergo decarboxylation. A comparative study of mandelic acid and mandelic acid-alpha(d) indicates the absence of primary kinetic isotope effect, ruling out the above possibility. It i s likely that acyl hypobromite is a precursor for oxidation at higher pH and the involvement of alkyl hypobromite cannot be ruled out at low er pH. The NBP and NBS oxidations of alpha-hydroxyacids are found to b e well correlated.