Kinetics of oxidation of 3-aminopropan-1-ol and related compounds by silver(III) species

Abstract

The oxidation of 3-aminopropan-1-ol (3-AP) and certain diamines by diperiodatoargentate(III) (DPA) has been studied by stopped-flow spectrophotometry at pH 8.0. The kinetics of the reaction of 3-AP consist of three steps—an induction period, then a fast decay, which is followed by a slower decay. The initial step involves the axial binding of the substrate to the silver(III) species; this rearranges during the induction period (0.2 s) and takes up another ligand in the following step with a second-order rate constant of 4 × 10³ dm³ mol⁻¹ s⁻¹ to yield [Ag^III(H₂IO₆)(3-AP)₂]. The silver(III) centre in this complex is reduced by 3-AP in the rate-determining step with a rate constant of 0.50 × 10² dm³ mol⁻¹ s⁻¹. Both of these processes show inverse dependence on [IO₄⁻] and [OH⁻]. The kinetics of the oxidation of diamines by silver(III) follow a different kinetic behaviour. The rates of their complexation and oxidation follow the order 1,2-diaminoethane > 1,3-diaminopropane > 1,4-diaminobutane. Separation of the two functional groups by an additional CH₂ in the studied substrates reduces the rates of both the steps. In case of the diamines, the formation of a cyclic complex involving silver(III) and the substrate prior to its oxidation is suggested. The mechanisms of these reactions are being analysed.