Pulsed-accelerated-flow (PAF) and stopped-flow techniques are used to study the kinetics of HNC12 and CH3NC12 reactions with sulfite. Pseudo-first-order rate constants with excess sulfite at p [H+] 3.7-6.4 are measured from 35-45000 sI (25.0'C, p= 0.50). Acid suppresses the rate because S0, H-is much less reactive than SO,,-. The rate expression is-d [RNCl,]/dr= kI [RNCl2][SO,"], where kl (MI sI) is 5.8 X 106 for HNCI, and 2.4 X IO'for CH, NCl2. The ...