Chlorination of amides: Kinetics and mechanisms of formation of N-chloramides and their reactions with phenolic compounds

Amides are common constituents in natural organic matter and synthetic chemicals. In this study, we investi-gated kinetics and mechanisms of the reactions of chlorine with seven amides, including acetamide, N-meth-ylformamide, N-methylacetamide, benzamide, N-methylbenzamide, N-propylbenzamide, and N-(benzoylglycyl) glycine amide. Apparent second-order rate constants for the reactions of the amides with chlorine at pH 8 are in the range of 5.8 x 10-3 -1.8 M- 1s- 1 and activation energies in the range of 62-88 kJ/mol. The second-order rate constants for the reactions of chlorine with different amides decrease with increasing electron donor character of the substituents on the amide-N and N-carbonyl-C in the amide structures. Hypochlorite (-OCl) dominates the reactions of chlorine with amides yielding N-chloramides with species-specific second-order rate constants in the range of 7.3 x 10-3 - 2.3 M- 1s- 1. Kinetic model simulations suggest that N-chlorinated primary amides further react with HOCl with second-order rate constants in the order of 10 M- 1s- 1. The chlorination products of amides, N-chloramides are reactive towards phenolic compounds, forming chlorinated phenols via electrophilic aromatic substitution (phenol and resorcinol) and quinone via electron transfer (hydroquinone). Meanwhile, N-chloramides were recycled to the parent amides. At neutral pH, apparent second-order rate constants for the reactions between phenols and N-chloramides are in the order of 10-4-0.1 M- 1s- 1, comparable to those with chloramine. The findings of this study improve the understanding of the fate of amides and chlorine during chlorination processes.