Iron(II)-chloramine-T reaction

When a large excess of the oxidant is used in the iron(II)-chloramine-T reaction at pH 2.56-5.6 the amount of oxidant consumed is well above the stoichiometric amount required to oxidize iron(II) to iron(III). This has been attributed to the formation and subsequent behaviour of free radicals during the reaction. The formation of free radicals has been experimentally demonstrated. They apparently dimerize to give products of the type R-NCl-NCl-R (R = CH(3)C(6)H(4)SO(2)), which are further oxidized by chloramine-T. The dimerized species liberate iodine very slowly from acidified potassium iodide. This explanation satisfactorily accounts for the observed extent and rate of destruction of excess of chloramine-T in presence of small amounts of Fe(II) or bromide at pH 2.65-4.70. The storage of chloramine-T in metal containers might cause extensive destruction of the oxidant by a similar free radical mechanism and should be avoided.