Kinetics and Mechanism of the BrO3(1-)-SCN(1-)-H(1+) Reaction

Article abstract of DOI:10.1021/j100182a037

The reaction of BrO3(1-) with SCN(1-) in dilute HClO4 is investigated in both batch and flow reactor modes.The stoichiometry of the reaction is BrO3(1-) + SCN(1-) + H2O -> HSO4(1-) + HCN + Br(1-) when SCN(1-) is in excess and 7BrO3(1-) + 5SCN(1-) + 2H(1+) -> 5BrCN + Br2 + 5SO4(2-) + H2O when BrO3(1-) is in excess.There is a two-stage induction period in the batch mode when BrO3(1-) is in excess before the occurrence of a third stage in which Br2 finally accumulates.The end of the first stage corresponds to the consumption of SCN(1-), and the end of the second corresponds to the consumption of CN(1-).Both of these species react rapidly with Br2.Bromine accumulates during the third stage as a result of the reaction of Br(1-) with BrO3(1-).A large range of feed-stream concentrations and flow rates was investigated in CSTR mode.No periodic or quasiperiodic oscillations were found that could not be eliminated by substituting gravity feeding for a peristaltic pump.However, the system is very sensitive to environmental perturbation and thus very noisy at low flow rates.The reaction is simulated on the basis of a mechanism proposed here.The agreement between experiments and simulations is very good.Simulations at low flow rates show a very rapid change with flow rate of steady-state along a line connecting the three stages mentioned above with BrO3(1-) in excess.This is likely the source of the experimental sensitivity to perturbation.