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 K_d′ 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.