Chloramines VII: Chlorination of Alanylphenylalanine in Model Solutions and in a Wastewater

Products of the 30-min chlorination of the dipeptide alanylphenylalanine were determined at pH 7.0 in model solutions. At Cl 2 /peptide mole ratios ≤1, N -chloroalanylphenylalanine ( I ) is the only product. I is very stable at 23 °C ( t 1/2 = 111 ± 8.8 h). At mole ratios ≥2, N, N -dichloroalanylphenylalanine ( II ) is the only product. II decomposes in model solutions ( t 1/ 2 = 4.1 ± 0.2 h) at pH 7.0 to form a compound identified as the N -chloroketimine N -[2-( N ‘-chloroimino)propanoyl]phenylalanine ( III ). The structure of III was identified by converting it to N -pyruvylphenylalanine tert -butyl ester by reduction, hydrolysis, and esterification and correlating the mass spectrum and GC retention time of this derivative with those of an authentic sample. III is unusually stable and decomposes slowly ( t 1/2 = 125 ± 6.5 h) to phenylalanine. In order to monitor the reactions of the dipeptide at low concentrations in a wastewater, alanyl- p -[ 3 H]-phenylalanine was synthesized. A primary wastewater (TKN = 19.82 mg/L; [NH 3 ] = 19.79 mg/L) was inoculated with the radiolabeled dipeptide and chlorinated to seven different chlorine concentrations spanning the breakpoint curve of the wastewater. Products identical to those observed in model solutions were formed. The stabilities of the tritiated analogs of II and III in the wastewater were similar to those determined in model solutions. Time studies of the decomposition of N, N- dichloroalanyl- p -[ 3 H]-phenylalanine revealed the formation of an intermediate ( A ) not previously recognized. Modeling of the reactions of II suggested that A was a decomposition product of III in the formation of phenylalanine and was probably either an isocyanate or a carbamic acid formed from hydrolysis of an isocyanate intermediate.