NONMETAL REDOX KINETICS - REACTIONS OF SULFITE WITH DICHLORAMINES AND TRICHLORAMINE

Pulsed-accelerated-flow (PAF) and stopped-flow techniques are used to study the kinetics of HNCl2 and CH3NCl2 reactions with sulfite. Pseudo-first-order rate constants with excess sulfite at p[H+] 3.7–6.4 are measured from 35–45 000 s−1 (25.0 °C, μ = 0.50). Acid suppresses the rate because SO3H− is much less reactive than SO32−. The rate expression is −d[RNCl2]/dt = k1[RNCl2][SO32−], where k1 (M−1 s−1) is 5.8 × 106 for HNCl2 and 2.4 × 107 for CH3NCl2. The initial nitrogen product is RNHCl, which reacts further with sulfite. Trichloramine reactions with sulfite are measured by the PAF method under second-order conditions with unequal concentrations (25.0 °C, μ = 0.50) from p[H+] 3.8 to 4.6. The rate expression is −d[NCl3]/dt = (k1[SO32−] + k2[SO3H−])[NCl3], where k1 is 4.5 × 109 M−1 s−1 and k2 is 1.4 × 107 M−1 s−1. The initial nitrogen product is HNCl2, which reacts further with sulfite. A Cl+-transfer mechanism is proposed for all the reactions with sulfite to give ClSO3− as an initial product that hydrolyzes to give Cl− and SO42−. The relative reactivities of active chlorine species with SO32− are NCl3 ≫ HNCl2 ≫ NH2Cl ≪ OCl−, where the NCl3 and HNCl2 reactions are suppressed by acid whereas the NH2Cl and OCl− reactions are acid assisted. © 1990, American Chemical Society. All rights reserved.