Kinetic and mechanistic study of bromination of sulfanilic acid with N-bromosuccinimide in alkaline medium

The sulfanilic acid (p-amino benzene sulfonic acid) (SNA) is an important and interesting compound which finds a number of applications in the syntheses of organic dyes. The amide of sulfanilic acid (sulfanilamide) and certain related substituted amides are of considerable medicinal importance as the sulfa drugs. The kinetics of bromination of SNA with N-bromosuccinimide (NBS) in NaOH medium has been studied at 308 K. The experimental rate law obtained is -d[NBS]/dt =[NBS][SNA](x)[OH-] where x is less than unity. The reaction was subjected to changes in concentration of succinimide, the reduction product of NBS, concentration of added neutral salt, as well as to dielectric permittivity and ionic strength of the medium. Solvent isotope effect has been studied using D2O. The stoichiometry of the reaction has been determined, and the products were identified and characterized. Activation parameters for the overall reactions have been computed using the Arrhenius plot. OBr- has been postulated as the reactive species of NBS. The reaction fails to induce polymerization of added acrylonitrile. The proposed mechanism and the derived rate law are consistent with the observed kinetic data.