Stoicheiometry, kinetics, and mechanism of the oxidation of hyponitrous acid by iodine in acetate buffers

Abstract

The reaction of hyponitrous acid with iodine occurs as (i) in the pH range 4–6 and at [I–] H2N2O2+ I2+⅙H2O → 2HI +½N2O +⅔NO +⅓HNO3(i) < 0.025 mol dm–3. One of the identified intermediates is HNO2 which is the main source of NO. Several reactions involving HNO2, H2N2O2, and iodide may follow. The decomposition of H2N2O2 is very significant at pH < 4 and [I–] > 0.025 mol dm–3, and the stoicheiometry Δ[H2N2O2]/Δ[I2] changes from 1 :1 to 2:1 or even 6:1. The rate law (ii) applies where Kd′ is the first acid-–d[I2]T/dt=KK′d[H2N2O2]T[I2]T/[H+](1 +K[I–])(ii) dissociation constant of H2N2O2 and K is the equilibrium constant for the formation of I3–; k was found to be (2.1 ± 0.1)× 104 dm3 mol–1s–1at 35 °C employing K′d= 6.3 ×10–8 mol dm–3 and K= 549 dm3 mol–1.