title: The action of chloride peroxidase on 4-chloroaniline. N-oxidation and ring halogenation.
abstract: Chloride peroxidase catalyses both the ring halogenation and N-oxidation reactions of 4-chloroaniline by H2O2 and either KCl or KBr. In the absence of any halide salt only the N-oxidation reaction was observed, with the resulting conversion of 4-chloroaniline into 4-chloronitrosobenzene. The N-oxidation reaction proceeded even more rapidly in the presence of Cl- or Br-, in spite of the fact that ring halogenation was also a rapid reaction. The enhancement of N-oxidation was highly dependent on the pH of the media and displayed an optimum in the region of pH 3.5-4.0. No rate enhancement was observed above pH 5.5. KF partially inhibited the rate of N-oxidation in a pH-dependent manner. On the basis of calculated catalytic-centre activity the N-oxidation reaction was the major reaction at pH 3.5 or higher, whereas the ring-halogenation reaction became the major reaction below pH 3.5. In the presence of high concentrations of 4-chloroaniline relative to H2O2 the reaction intermediate, 4-chlorophenylhydroxylamine, was detected for the first time in a chloride peroxidase-catalysed reaction with this arylamine substrate. These findings were interpreted on the basis of current knowledge concerning the mechanism of action of chloride peroxidase.
mesh_terms: D000814:Aniline Compounds / Q000378:metabolism*; D001665:Binding Sites; D001965:Bromides / Q000494:pharmacology; D002711:Chloride Peroxidase / Q000378:metabolism*; D002712:Chlorides / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000378:metabolism*; D011485:Protein Binding
chemical_list: D000814:Aniline Compounds; D001965:Bromides; D002712:Chlorides; D010544:Peroxidases; D002711:Chloride Peroxidase; C004658:4-chloroaniline