15541-45-4Relevant academic research and scientific papers
Kinetics and mechanisms of the reactions of hypochlorous acid, chlorine, and chlorine monoxide with bromite ion
Nicoson, Jeffrey S.,Perrone, Thomas F.,Huff Hartz, Kara E.,Wang, Lu,Margerum, Dale W.
, p. 5818 - 5824 (2008/10/08)
The reaction between BrO2- and excess HOCl (p[H +] 6-7, 25.0 °C) proceeds through several pathways. The primary path is a multistep oxidation of HOCl by BrO2- to form ClO3- and HOBr (85% of the initial 0.15 mM BrO 2-). Another pathway produces ClO2 and HOBr (8%), and a third pathway produces BrO3- and Cl - (7%). With excess HOCl concentrations, Cl2O also is a reactive species. In the proposed mechanism, HOCl and Cl2O react with BrO2- to form steady-state species, HOClOBrO - and ClOClOBrO-. Acid facilitates the conversion of HOClOBrO- and ClOClOBrO- to HOBrOClO-. These reactions require a chainlike connectivity of the intermediates with alternating halogen-oxygen bonding (i.e. HOBrOClO-) as opposed to Y-shaped intermediates with a direct halogen-halogen bond (i.e. HOBrCl(O)O -). The HOBrOClO- species dissociates into HOBr and ClO2- or reacts with general acids to form BrOClO. The distribution of products suggests that BrOClO exists as a BrOClO·HOCl adduct in the presence of excess HOCl. The primary products, ClO 3- and HOBr, are formed from the hydrolysis of BrOClO·HOCl. A minor hydrolysis path for BrOClO·HOCl gives BrO3- and Cl-. An induction period in the formation of ClO2 is observed due to the buildup of ClO 2-, which reacts with BrOClO·HOCl to give 2 ClO2 and Br-. Second-order rate constants for the reactions of HOCl and Cl2O with BrO2- are k1HOCl = 1.6 × 102 M-1 s -1 and k1Cl2O = 1.8 × 105 M-1 s-1. When Cl- is added in large excess, a Cl2 pathway exists in competition with the HOCl and Cl2O pathways for the loss of BrO2-. The proposed Cl 2 pathway proceeds by Cl+ transfer to form a steady-state ClOBrO species with a rate constant of k1Cl2 = 8.7 × 105 M-1 s-1.
Oxygen-Transfer Reactions of Methylrhenium Oxides
Abu-Omar, Mahdi M.,Appelman, Evan H.,Espenson, James H.
, p. 7751 - 7757 (2008/10/09)
Methylrhenium dioxide, CH3ReO2 (or MDO), is produced from methylrhenium trioxide, CH3ReO3 (or MTO), and hypophosphorous acid in acidic aqueous medium. Its mechanism is discussed in light of MTO's coordination ability and the inverse kinetic isotope effect (kie): H2P(O)OH, k = 0.028 L mol-1 s-1; D2P(O)OH, k = 0.039 L mol-1 s-1. The Re(V) complex, MDO, reduces perchlorate and other inorganic oxoanions (XOn-, where X = Cl, Br, or I and n = 4 or 3). The rate is controlled by the first oxygen abstraction from perchlorate to give chlorate, with a second-order rate constant at pH 0 and 25°C of 7.3 L mol-1 s-1. Organic oxygen-donors such as sulfoxides and pyridine N-oxides oxidize MDO to MTO as do metal oxo complexes: V(aq)2+, VO2+(aq), HOMoO2+(aq), and MnO4-. The reaction between V(aq)2+ with MTO and the reduction of VO2+ with MDO made it possible to determine the free energy for MDO/MTO. Oxygen-atom transfer from oxygen-donors to MDO involves nucleophilic attack of X-O on the electrophilic Re(V) center of MDO; the reaction proceeds via an [MDO-XO] adduct, which is supported by the saturation kinetics observed for some. The parameters that control and facilitate the kinetics of such oxygen-transfer processes are suggested and include the force constant for the asymmetric stretching of the element-oxygen bond.
Kinetics of Disproportionation and pKa of Bromous Acid
Faria, Roberto de Barros,Epstein, Irving R.,Kustin, Kenneth
, p. 1363 - 1367 (2007/10/02)
The kinetics of the disproportionation reaction of bromine(III), 2Br(III)->Br(I) + Br(V), was studied in phosphate buffer, in the pH range 5.9-8.0, by monitoring optical absorbance at 294 nm using stopped-flow.The dependences on aH+ and were of order 1 and 2, respectively, and no dependence on was found.The reaction was also studied in acetate buffer, in the pH range 3.9-5.6.Within experimental error, no evidence was found for a direct reaction between two BrO2- ions.This study yields rate contants 39.1+/-2.6 M-1s-1 for the reaction HBrO2 + BrO2 -> HOBr + BrO3- and 800+/-100 M-1s-1 for the reaction 2HBrO2 -> HOBr + BrO3- + H+ and an eqilibrium quotient for HBrO2 H+ + BrO2- of 3.7+/-0.9X10-4 M (pKa=3.43) at ionic strength 0.06 M and 25.0+/-0.1 degree C.The bromous acid dissociation constant is essentially identical to the value previously obtained from kinetics study of the bromine(III)-I reaction (J.Phys.Chem. 1992, 96, 6861).
Inorganic Bromate Oscillators. Bromate-Manganous-Reductant
Alamgir, Mohamed,Orban, Miklos,Epstein, Irving R.
, p. 3725 - 3728 (2007/10/02)
A family of systems containing bromate and manganous ions and an inorganic reductant such as hydrazine, sulfite, arsenite, stannous, or iodide ion exhibits sustained oscillations in a flow reactor.These systems show bistability as well.Model calculations predict limit cycle behavior if the bromide flow of the minimal bromate oscillator is replaced by a flow of a reductant which generates bromide from Br2 and/or HOBr sufficiently rapidly.
On the Use of Ion-Selective Electrodes for Monitoring Oscillating Reactions. 2. Potential Response of Bromide- and Iodide-Selective Electrodes in Slow Corrosive Processes. Disproportionation of Bromous and Iodous Acids. A Lotka-Volterra Model for the Halate Driven Oscillators
Noszticzius, Z,Noszticzius, E.,Schelly, Z. A.
, p. 510 - 524 (2007/10/02)
The potential response of silver halide membrane electrodes to the corrosive bromous, bromic, iodous, and iodic acids is investigated in sulfuric acid solutions ( = 0.15 and 1.5 M), typical media for several well-known oscillating reactions.The syntheses of the materials (bromide-free NaBrO2 and HIO2) needed for the experiments are described.The potentials recorded as a function of time were used for the determination or estimation of several rate constants at 24 +/- 1 deg C: the disproportionation rate constant of HBrO2 is kB1 = (1.4 +/- 0.2) * 103 M-1 s-1 (in 0.15 M H2SO4) and (3.8 +/- 1.0) * 103 M-1 s-1 (in 1.5 M H2SO4): the corresponding value for HIO2 is KI1 -1 s-1 (in 0.05-0.15 M H2SO4); the disproportionation of HIO2 is autocatalytic, the rate-determining step is a reaction of HIO2 with H2OI+, the rate constant of which is kI5 = 130 +/- 5 M-1 s-1 ( in 0.15 M H2SO4); the rate constants of the reactions of HBrO2 with Br- and H+, and HIO2 with I- and H+ are 106 B2 6 M-2 s-1 (in 1.5 M H2SO4) and 106 I2 7 M-2 s-1 (in 0.15 M H2SO4), respectively.The corrosive reactions of the halous and halic acids with halide ions are much slower than those of hypohalous acids, which fact required the development of the theory for slow corrosive reactions.Criteria for the definitions of slow and fast corrosive reactions are given.The possibility of a second autocatalytic process in the halate driven oscillating reactions is demonstrated.On the basis of these results, a generalized Lotka-Volterra scheme is proposed for the BZ, BL, and BR oscillators.
A Pulse Radiolysis Investigation of the Reactions of BrO2. with Fe(CN)64-, Mn(II), Phenoxide Ion, and Phenol
Field, R. J.,Raghavan, N. V.,Brummer, J. G.
, p. 2443 - 2449 (2007/10/02)
The single-electron reductions of BrO2. by Fe(CN)64-, phenoxide ion, Mn(II), and phenol have been investigated.The BrO2. was produced by pulse radiolysis of aqueous solutions of BrO3- which also contained one of these reductants.All experiments were carried out at pH 6-12.The reductions by Fe(CN)64- and phenoxide ion were rapid and clean and led to the products Fe(CN)63- and phenoxy radical.The rate constants for these reductions were found to be, respectively, (1.9+/-0.1)E9 and (2.6+/-0.2)E9 M-1 s-1.The reductions of BrO2. by Mn(II) and phenol were found to be much slower as well as more complex than the reductions by Fe(CN)64- and phenoxide ion.The products were, as expected, Mn(III) and phenoxy radical.However, there was a component of BrO2. reduction by Mn(II) whose rate did not depend upon .Furthermore, the rate of BrO2. reduction by phenol did not depend at all upon the concentration of phenol.It is suggested that these slower reductions were complicated by the well-known dimerization equilibrium between BrO2. and Br2O4.If the rate of reduction of this dimer by Mn(II) or phenol is comparable to or faster than the rate of its return to BrO2., then the dimerization process itself will become partially or completely rate determining; thus the less than expected dependence of the rates of these reductions on reductant concentrations may be rationalized.Regardless of the exact mechanism of the process, it was shown that the reduction of BrO2. by Mn(II) and phenol proceeds with the stoichiometry and overall time scale inferred from studies of the reduction of BrO3- by some weak metal-ion reductants and of catalyzed (Belousov-Zhabotinsky reaction) and uncatalyzed bromate-driven chemical oscillators.
