Kinetics and mechanism of oxidation of iron(II) by N-chloro-p-substituted-benzenesulfonamides

The kinetics of oxidation of Fe-II by N-chloro-N-sodiobenzenesulfonamide (c hloramine-B, CAB), N-chloro-N-sodio-p-methylbenzenesulfonamide (chloramine- T. CAT or CAMB), N-chloro-N-sodio-p-ethylbenzenesulfonamide (CAEB), N-chlor o-N-sodio-p-chlorobenzenesulfonamide (CACB), N-chloro-N-sodio-p-bromobenzen esulfonamide (CABB) and N-chloro-N-sodio-p-iodobenzenesulfonamide (CAIB) in aqueous sulfuric acid medium have been investigated. The observed kinetics of first order in [oxidant], fractional order each in [Fe-II] and [SO42-], and inverse fractional order in [H+] have been explained by a mechanism in volving the formation of an intermediate by the direct interaction between the oxidising species ArSO2NH2Cl+ and [Fe-II], which subsequently undergoes disproportionation in the rate-determining step leading to Fe-III, respect ive sulfonamide and Cl-. The related rate law has been deduced. The activat ion parameters have also have computed. The constancy of the free energies of activation may signal the operation of similar mechanism in all the case s.