Chloraminometric and bromaminometric oxidation of sulfanilic acid in alkaline medium: A comparative kinetic and mechanistic study

Abstract

AbstractThe kinetics of oxidation of sulfanilic acid (SAA) by chloramine‐B (CAB) and bromamine‐B (BAB) has been investigated in alkaline medium at 35 ± 0.1°C. The oxidation reaction follows identical kinetics in the case of both the oxidants with first‐order dependence on each [oxidant]o and [SAA]o and an inverse first‐order dependence on [OH−]. The variation of ionic strength, dielectric constant of the medium, addition of the reaction product (benzenesulfonamide), and halide ions showed no significant influence on the reaction rate. Proton inventory studies made in H2O–D2O mixtures for CAB and BAB have been utilized to calculate the isotopic fractionation factor. The reaction has been studied at different temperatures, and activation parameters for the composite reaction have been computed from the Arrhenius plots. N‐Hydroxylaminobenzene‐4‐sulfonic acid was identified as the oxidation product of SAA from IR and GC‐MS analysis. A mechanism consistent with the kinetic results is proposed in which PhSO2NHX (X = Cl or Br) interact with the substrate in the rate‐limiting step. A suitable rate law is derived. The rate of oxidation of sulfanilic acid is about fourfold faster in BAB compared to CAB. The oxidation of SAA brought about by CAT and BAT was also investigated under identical experimental conditions, and the overall rate of oxidation of SAA increases in the order: BAB > BAT > CAB > CAT. This may be attributed to the difference in electrophilicities of Cl+ and Br+ ions and also the van der Waal's radii of chlorine and bromine. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 48–56, 2006