REACTIONS OF MONOCHLORAMINE WITH BR-2, BR-3(-), HOBR, AND OBR- - FORMATION OF BROMOCHLORAMINES

Pulsed-accelerated-flow and stopped-flow spectroscopies are used to measure rate constants for the reactions of NH2Cl with Br-2, Br-3(-), HOBr,and OBr-: NH2Cl+Br-2->(NHBrCl)-N-kBr2+Br-+H+;(NHCl)-Cl-2+Br-3(-)->(NHBrCl)-N-kBr3+ 2Br(-)+H+;NH2Cl+HOBr->(kHOBr) NHBrCl+H2O; NH2Cl+OBr-->(kOBr) NHBrCl+OH-, Rate constants (25.0 degrees C) are k(Br2)=(4.18 +/- 0.05) X 10(8) M-(1)s-(1), k(Br3)=(3.07 +/- 0.24) X 10(7)M(-1)s-(1), k(HOBr)=(2.86 +/- 0.06) X 10(5)M(-1) s(-1), and k(OBr)=(2.20 +/- 0.06) x 10(4)M(-1)s(-1). In each reaction, nucleophilic attack of the nitrogen lone electron pair facilitates a Br+ transfer from the bromine species to form the mixed haloamine NHBrCl, which decomposes slowly relative to its rate of formation. With the bromine species in excess, NBr2Cl forms rapidly and subsequently decays with a half-life of similar to 5 min at pH 6.2. Aqueous molar absorptivities for NBr2Cl are estimated as 4400 M(-1) cm(-1) at 242 nm and 550 M(-1) cm(-1) at 300 nm.