# Oxidation of Aromatic Side Chains

## Oxidation of Aromatic Side Chains: Eperimental Procedure

In most cases, oxidations with KMnO4 are carried out in a two-phase system. Since KMnO4 is insoluble in non-polar hydrocarbons, is achieved by adding a few moles of a transfer catalyst (crown ether or tetraalkylammonium salts) to the system.

To an aqueous solution of phase-transfer catalyst (0.5 $mL$) and sodium carbonate is added the alkyl-substituted aromatic compound and the oxidizing reagent potassium permanganate in a ratio of 1:7. Proper cautionary steps should be taken because under certain conditions the reaction might be strongly exothermic The mixture is heated under reflux until disappearance of the permanganat color (ca. 45 $min$). After filtration of manganese dioxide, the carboxylic acid is recrystallized. Impurities caused by excess manganese dioxide can be removed by treatment with hydrogen sulfite or oxalic acid.

Fig.1

A possible, alternative methodology using nitric acid as oxidizing agent (see lower reaction) practically is of no importance.

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