Manganese(II) Catalysed Oxidation of Aromatic Amines by Hydrogen Peroxide and lts Application to the Chelatometric Determination of Manganese

Abstract

Manganese(II)catalyses the hydrogen peroxideoxidation of aromatic amines such as phenetidine, P-anisidine, o-anisidi ne, etc, in aqueous carbonate so1utions, Cgbalt(II) and copper(ll) catalyse also the reaction in sodium bicarbonate (pH 8.4) and in ammonium carbonate solution (pH 9.3), respectively. This catalytic reaction was utilized to indicate the end'point of titration in the determinationof Mn(II)with EDTA.The optimum of the catalytic action of manganese(II)ion was found to be limited to relatively high carbonate concentration (O.4 mol/1) and narrow pH ranges (between 8 and 9.5), The recommended procedure for manganese determination was as follows to about 50 ml portion of O.4 mol/l carbonate solution containing known amounts of EDTA, add 3 ml'of O.2% P phenetidine (or P-anisidine) and 1 ml of 3% hydrogen peroxide. Titrate the solution with manganese(ll) solution. At the end point, the solution turned deep orange immediately by the formation of quinoneimines.this catalytic titration method was applied to determine zinc, cadmium, mercury and lead by'back-titrationof excess of EDTA with standard manganese(II)solution. The results were in good agreement with those obtained by the titrimetric method using BT or XO as metal indicator.The catalytic titration of manga: nese(II)with o-dianisidine and o-tolidine was also investigated.