Oxidation of p-Toluic Acid in Molten Potassium Hydroxide with Various Metal Oxides

Studies on the Oxidation of Toluic Acids in Molten Potassium Hydroxide. III

Abstract

The oxidation of p-toluic acid in molten potassium hydroxide was studied with various metal oxides under an normal pressure of air. It was found that p-toluic acid is oxidized to terephthalic acid with silver (I) oxide, vanadium (V) oxide, iron (III) oxide, mercury (II) oxide, molybdenum (VI) oxide, cobalt (III) oxide, thallium (III) oxide, copper (II) oxide, copper (I) oxide and potassium chromate.
The oxidation is mainly performed with the decrease of the oxidation number of the metals in the potassium salts of metallic acids which are formed from metal oxides dissolving in molten potassium hydroxide.
A higher yield of terephthalic acid was obtained by the use of the metal compound in higher oxidation state. In general, terephthalic acid was formed in higher yield with a metal compound of smaller standard oxidation reduction potential (E^O_B) in alkaline medium such as MnO₄^2-→MnO₂, Ag₂O→Ag and PbO₂→PbO.
From this general rule one can expect what substance is effective in this oxidation process. As an example, oxygen (E^O_B = -0.401 volt) can be used under an initial pressure of 30 kg/cm² to give terephthalic acid in 83 mol % yield from p-toluic acid. Thus it can be used as a new oxidation method of organic compounds.