Kinetics of Oxidation of 3- and 5-formylsalicylic Acids with Potassium Permanganate in Alkaline Medium

The kinetics of oxidation of 3-formylsalicylic acid (3-fsa) and 5-formylsalicylic acid (5-fsa) with potassium permanganate in alkaline medium (pH ∼ 12) have been studied spectrophotometrically. The oxidation involved the formyl group converting it to the corresponding carboxylic group. The oxidation products have been isolated and characterized by IR and Mass spectra. The reaction showed a first order with respect to permanganate and a fractional first order with respect to the two acids. The formation of short-lived hypomanganate (V) and manganate (VI) intermediates has been confirmed spectrophotometrically. The activation parameters have been determined. Quantum chemical calculations through density functional theory (DFT) at the B3LYP/6–31G(d) level predict an easy oxidation of 5-fsa than 3-fsa which agreed with the experimental results and a mechanism for the reaction is suggested.