NONMETAL REDOX KINETICS - OXIDATION OF BROMIDE ION BY NITROGEN TRICHLORIDE

Bromide ion reacts with NCl3 to generate NBrCl2 with the rate expressi on d[NCl3]/dt = 12[B ($) over bar r][NCl3] (M (s-1) at 25.0 degrees C, mu = 0.50 M). The NBrCl2 intermediate subsequently reacts with B ($) over bar r to give N-2, Br-2, and Cl- with the rate expression -d[NBrC l2]/dt = (0.05 + 5.3[B ($) over bar r])[NBrCl2]. The overall stoichiom etry from pH 3.2 to 6.5 corresponds to 2NCl(3) + 6B ($) over bar r --> N-2 + 3Br(2) + 6Cl(-). Rate constants for NCl3 reactions show extreme sensitivity to nucleophilic strength with SO32- > CN- > I- much great er than B ($) over bar r. Aqueous absorption spectra are determined fo r NCl3 with maxima at 336 nm (epsilon 190 M(-1) cm(-1)) and 220 nm (ep silon 5320 M(-1) cm(-1)) and for NBrCl2 with a maximum at 228 nm (epsi lon 4800 M(-1) cm(-1)). Spectral bands for NCl3, NBrCl2, NBr2Cl, and N Br3 shift systematically with the number of bromine atoms from 220 to 256 nm. The rate constants for the reactions of NHCl2 with Br-2, HOBr, and B ($) over bar r are much larger than that for the reaction of NC l3 with B ($) over bar r.