New pathways for chlorine dioxide decomposition in basic solution

The product distribution from the decay of chlorine dioxide in basic solution changes as the ClO2 concentration decreases. While disproportionation reactions that give equal amounts of ClO2- and ClO3- dominate the stoichiometry at millimolar or higher levels of ClO2, the ratio of ClO2- to ClO3- formed increases significantly at micromolar ClO2 levels. Kinetic evidence shows three concurrent pathways that all exhibit a first-order dependence in [OH-] but have variable order in [ClO2]. Pathway 1 is a disproportionation reaction that is first order in [ClO2]. Pathway 2, a previously unknown reaction, is also first order in [ClO2] but forms ClO2- as the only chlorine-containing product. Pathway 3 is second order in [ClO2] and generates equal amounts of ClO2- and ClO3-. A Cl2O4 intermediate is proposed for this path. At high concentrations of ClO2, pathway 3 causes the overall ClO3- yield to approach the overall yield of ClO2-. Pathway 2 is attributed to OH- attack on an oxygen atom of ClO2 that leads to peroxide intermediates and yields ClO2- and O2 as products. This pathway is important at low levels of ClO2.