Kinetic investigation of the reaction of pertechnetate with thiourea in a hydrochloric acid solution

Reactions of pertechnetate ion with thiourea (tu) in a hydrochloric acid solution have been investigated by spectrophotometry. Two consecutive reactions were observed for the formation of a technetium-thiourea complex. The intermediate is considered to be a Tc(V)-tu complex ([TcO(tu)₄]³⁺). The observed reaction rates of these two reactions were found to be second order with respect to the concentration of thiourea. The rate-determining step in the 1st step was concluded tobe the reduction of Tc(VII) to Tc(V) and that in the 2nd step to be the reduction of Tc(V) to Tc(III).