Rate of the Bromous Acid-Bromide Reaction Measured in a Br₂-HOBr Buffer System in Sulfuric Acid Solution

Abstract

In the Belousov-Zhabotinsky system bromine species of oxidation states - 1 to 5 are important for the start and for the inhibition of the autocatalytic reaction steps. Especially, the reaction of Br

Bromous acid/cerium(4+): reaction and HBrO2 disproportionation measured in sulfuric acid solution at different acidities

“…(1 + A:4a[H+])2 (10) We assume that the extinction coefficients of the protonated and unprotonated bromous acid are essentially the same (we could not detect a measurable difference when we determined the extinction coefficient of bromous acid solutions at different acidities), so the measured absorbance A can be attributed to the total concentration [HBr02]tot• This way the experimental rate constant &4 as defined in (2) can be expressed by fc4 ~*41>C (11) Surprisingly, the values obtained for k4 increase from 2200 M-> s-' in 0.5 M H2SO4 to 8000 M"1 s"1 in 2.0 M H2S04. A similar result was found by Noszticzius et al,9 who followed the disproportionation reaction electrochemically in 0.15 and 1.5 M sulfuric acid solutions.…”

“…That means the disproportionation reaction of HBr02 involves at least one protonation step. The only possible reaction path explaining the dependence on the acidity is the formation of the protonated species H2Br02+ as a reactive compound;14 HBr02 + H+ H2Br02+ HBr02 + H2Br02+ -HOBr + BrQ3" + 2H+ (R4a) is treated as a fast equilibrium: From (11) we expect that the experimental fc4 values increase linearily with C, which expression depends on the acidity of the solution. In Figure 5 the experimental £4 values are plotted as a function of C for = 0.02 M_1 (K^t reated as an adjustable parameter; numerical data in Table II; [H+] calculated from the sulfuric acid concentration using the data from Robertson and Dunford15).…”

“…Fit) and Acidity Function C (Calculation from(10) with £4. = 0.02 M'1) at Different Sulfuric concentrations are taken from the data ofRobertson and Dunford.15 Values in brackets: k* extrapolated from(11) with L*b = 1.7 X 105 M-> s->.…”

Activation Energy for the Disproportionation of HBrO2and Estimated Heats of Formation of HBrO2and BrO2

“…Only quite crude measurements of activation energies of a few members of reactions 1−7 are available. , We further report here an experimental investigation of the kinetics of disproportionation of HBrO 2 (reaction 4) at various temperatures and acidities and derive its activation parameters.…”

Contribution of Malonyl Radical Control in the Classical Belousov-Zhabotinsky Reaction

“…On the other hand, the reduced form of the catalyst (like Ce 3 + ) is oxidized by acidic bromate. The latter reaction proceeds by an autocatalytic process involving Br0 2 radicals and HBr0 2 [2], [3], The autocatalytic reaction can be switched off by species reacting with Br0 2 directly (like malonyl radicals [4] ) or with HBr0 2 (like Br" [5], [6], [7]). In the original theory of the BZ reaction developed by Field, Körös and Noyes (FKN) [8] it is assumed that bromide is the only control variable.…”