Oxidation of Indigo Carmine by <i>N</i>-Haloarenesulfonamidates: A Kinetic Study

Abstract

Abstract Kinetics of oxidation of indigo carmine (IC) by sodium N-haloarenesulfonamidates (RNXNa, where R=CH3C6H4SO2− or C6H5SO2− and X=Cl or Br) chloramine T (CAT), bromamine T (BAT), chloramine B (CAB), and bromamine B (BAB) in alkaline buffer (pH 9–11) has been followed spectrophotometrically at λmax=610 nm. Rate law, –d[IC]/dt=k[OX]0[IC]0[OH−]x where x&amp;lt;1, is obeyed. The reaction products, benzenesulfonamide and toluenesulfonamide retard the rate. Sulfonated anthranilic acid formed was quantitatively determined. Variation of ionic strength or dielectric constant of medium and addition of halide ions have no effect on the reaction. A two pathway mechanism is proposed in which the hypohalous acid (HOX) and the anion of N-haloamine RNX− interact with the substrate in rate limiting steps. The rate increases in the order: BAT&amp;gt;BAB&amp;gt;CAT&amp;gt;CAB, which is attributed to the difference in electrophilicities of halogen cations Br+ and Cl+ involved in the oxidation process and the ease with which these species are formed in reactions.