Kinetic study of the reduction of bromate ion by neptunium(V) in perchlorate solution

Abstract

The empirical form of the rate law for the reaction 4Np(V) + Br(V) = 4Np(VI) + Br(I) at 25°in perchloric acid-lithium perchlorate solutions is -d[Br(V)] /dt = k0 [Br(V)]2 [H+]1 •51. This expression adequately correlates the kinetic data from 10 to 90% reaction over a large range of initial reactant concentrations. At least one induction period is observed. A complex reaction scheme is proposed in which the rate parameter is identified as [fca2[H+]2/4&Co]/[l + (&Cl/fcCo)[H*] ], where k& is the rate constant for the reaction between brómate ion and a bromous acid intermediate, and kC(¡ and kc are rate constants of parallel paths for the disproportionation of the same intermediate. Comparisons with other systems in which brómate ion is reduced by weak one-electron reductants are made.H202 ,17 and Br~,7 however, the sole fate of the bromous acid appears to be reduction to hypobromous acid.Clearly, the demonstration of the validity of the full reaction scheme (a)-(c) proposed for these intriguing systems will require considerable additional investigation. The present study, because of its apparent simplicity, will hopefully provide a foundation on which further results can be added.

Bromate Oxidation of Ammonium Salts: In Situ Acid Formation for Reservoir Stimulation

“…Interestingly, kinetics similar to the bromate-ammonium system have previously been observed between ferrocyanide and BrO 3 – in acidic medium, where the bromide-bromate couple dominates the kinetic behavior . It has been shown that the direct reaction between BrO 3 – and a reducing agent (Red) is slow and does not contribute to the reaction rate. , However, BrO 3 – and Br – in the presence of H + can form HOBr and HBrO 2 or vice versa. − Therefore, a more complex reaction scheme for bromate’s oxidation of NH 4 + (Red) may be realized as BrO 2 · is formed and reacts with NH 4 + (Scheme ) as it has been described in generalized form and as in a recent example by Olangunju and Simoyi . Consistent with this proposed scheme is the fact that the p K a of isoelectronic HClO 2 is 1.92.…”

“…44 It has been shown that the direct reaction between BrO 3 − and a reducing agent (Red) is slow and does not contribute to the reaction rate. 45,46 However, BrO 3 − and Br − in the presence of H + can form HOBr and HBrO 2 or vice versa. 47−49 Therefore, a more complex reaction scheme for bromate's oxidation of NH 4 + (Red) may be realized as BrO 2 • is formed and reacts with NH 4 + (Scheme 4) as it has been described in generalized form 50 and as in a recent example by Olangunju and Simoyi.…”

Mechanistic studies on the vanadium(II) and vanadium(III) reductions of iodate and bromate

“…In the limit as /? -*-0, the observed rate constant should approach half of the rate constant observed when V(III) is in large excess and reaction proceeds through (9) and (11). From Figure 2 it can be seen that although the upper limit is apparently reached, a lower limit is not and the ratio of intercept to limiting values is approximately 1:1.7.…”

“…The rates of formation of I2 and V02+ are first order in [V3+] and [I(V)], where ki can be defined as 2d The precise identity of the intermediate dose not affect the discussion. As the relative concentration of V(III) drops {R decreases), reaction 10 becomes more important compared with (11), and the observed rate constant decreases as reaction 10 re-forms I(V). In the limit as /?…”

Pressure Dependence of Carbonate Exchange with [NpO2(CO3)3]4– in Aqueous Solutions

“…The bound neptunium was eluted as Np(V) using 0.3 M HNO 3 . The stock was then oxidized to Np(VI) using excess KBrO 3 , 19 and the progress of the oxidation was monitored via UV−vis. The absence of the strong Np(V) peak at 981 nm and the presence of the Np(VI) peak at 1226 nm were considered strong evidence of complete oxidation to Np(VI).…”