The method of oxidizing organic compounds, such as 1,3,5-trichlorobenzene, in an aqueous system of pH not more than about 4, the method comprising oxidizing the organic compound by contacting the compound with an oxidizing agent, such as air, in the aqueous system in the presence of a catalytic amount of a cocatalyst system, is improved by using as the cocatalyst system a catalytic combination of nitrate ions, at least one of either bromide ions or iodide ions, and transition metal ions of at least one transition metal having two or more oxidation states, such as vanadium ions. This cocatalyst system enhances the rate of oxidation of the organic compounds.