Kinetics of Hypobromous Acid Disproportionation

Abstract

The kinetics of aqueous hypobromous acid disproportionation are measured at 25.0 degrees C from p[H(+)] 0.2 to 10.2. The reactions are second order in HOBr with a maximum rate at pH 3-8. The rate of disproportionation decreases significantly above pH 8 as OBr(-) forms. Another suppression observed below pH 3 is attributed to the reversibility of initial steps in the decomposition. The rate expression is given by -d[Br(I)]/dt = n{(c/(c + [H(+)])k(1a) + k(B)[B])[HOBr](2) + k(1b)[OBr(-)](2)}, where k(1a) = 2 x 10(-)(3) M(-)(1) s(-)(1), k(B)[B] is a general-base-assisted pathway, k(1b) = 6 x 10(-)(7) M(-)(1) s(-)(1), n is a stoichiometric factor that ranges from 2 to 5, and c is a ratio of rate constants that is equal to 0.03 M. Decomposition is catalyzed by HPO(4)(2)(-) (k(B) = 0.05 M(-)(2) s(-)(1)) and by CO(3)(2)(-) (k(B) = 0.33 M(-)(2) s(-)(1)). Above pH 8, the first observable product is BrO(2)(-) (initially n = 2). Below pH 4, n = 5 due to Br(2) and BrO(3)(-) formation. From pH 4 to 7, n varies from 5 to 3. A detailed mechanism is presented.

Enhanced Bromate Formation during Chlorination of Bromide-Containing Waters in the Presence of CuO: Catalytic Disproportionation of Hypobromous Acid

“…Bromate concentrations increase slowly within the first 15 min, implying that a build-up of an intermediate, probably bromite, is necessary before bromate is formed. 15 After 15 min the concentration of bromate started to increase until most of the HOBr was depleted.…”

“…15,16 The disproportionation of HOBr is the reaction in which HOBr (i.e., Br(+I)) reacts with itself, leading to a reduced species (Br − , Br(−I)) and to oxidized species (BrO 2 − , Br(+III), BrO 3 − , Br(+V)). …”

Energy cycle based on a high specific energy aqueous flow battery and its potential use for fully electric vehicles and for direct solar-to-chemical energy conversion

“…The kinetics of the bromine disproportionation (8) has been studied mostly in near-neutral media (4≤pH≤ 8) [58,59] where the rates of various steps fall in the range convenient for experimental measurements. The process is rather complex (the corresponding reactions for chlorine being even more complex) [60][61][62][63] [73,74].…”

“…The chlorine disproportionation in basic solutions also follows a general base catalysis route, first order in Cl 2 and in the general base, while the reverse comproportionation reaction is first order in HOCl, Cl − , and in the general acid [79]. The hypobromite formed in (10) and (11) can undergo a further disproportionation which is strongly pH dependent [59]. At a low pH, bromine and bromate are formed:…”

Enhanced formation of bromate and brominated disinfection byproducts during chlorination of bromide-containing waters under catalysis of copper corrosion products

“…, while no further reaction proceeds between HOCl and HOBr (Kumar and Margerum, 1987;Beckwith and Margerum, 1997;Margerum and Huff Hartz, 2002). Although the disproportionation of HOBr still occurs, bromate (BrO 3 À ) formation during chlorination of Br À -containing waters is usually insignificant because of the slow reaction rate (<10 À2 M À1 s À1 ) (Liu et al, 2012).…”