Dichloramine decomposition in the presence of excess ammonia

Abstract

The decomposition of aqueous dichloramine in the presence of excess ammonia was studied to verify a proposed decomposition mechanism. Experiments were conducted under conditions in which the three significant reactions were isolated from others that could potentially complicate interpretation of results. The decomposition of dichloramine, producing primarily nitrogen gas and monochloramine, was initiated by mixing solutions of dichloramine and monochloramine under varying experimental conditions of pH, phosphate concentration, and initial dichloramine and monochloramine concentration. The chloramine concentrations were then monitored titrimetrically with time. Rate constants characterizing the reactions were determined using nonlinear least squares regression analysis and the reaction stoichiometry determined by comparing dichloramine loss to monochloramine formed. Phosphate did not catalyze the decomposition which suggests that the mechanism does not involve general base catalysis. A mechanism including a direct reaction of monochloramine was indicated based on both kinetic and stoichiometric considerations. The experimental results obtained at a high initial ratio of dichloramine to monochloramine could be reasonably predicted with the proposed mechanism and one set of rate constants. However, the constants were somewhat dependent on the initial dichloramine ratio. This discrepancy may be due to the existence of another reaction(s) not included in the proposed mechanism.