Bromate ions

The existence of chaotic oscillations has been documented in a variety of chemical systems. Some of tire earliest observations of chemical chaos have been on biochemical systems like tire peroxidase-oxidase reaction [12] and on tire well known Belousov-Zhabotinskii (BZ) [13] reaction. The BZ reaction is tire Ce-ion-catalyzed oxidation of citric or malonic acid by bromate ion. Early investigations of the BZ reaction used tire teclmiques of dynamical systems tlieory outlined above to document tire existence of chaos in tliis reaction. Apparent chaos in tire BZ reaction was found by Hudson et a] [14] aiid tire data were analysed by Tomita and Tsuda [15] using a return-map metliod. Chaos was confinned in tire BZ reaction carried out in a CSTR by Roux et a] [16, E7] and by Hudson and... 

The equation for the reaction between iodide and bromate ions in acidic solution is... 

A voltaic cell consists of two half-cells. One of the half-cells contains a platinum electrode surrounded by chromium(III) and dichromate ions. The other half-cell contains a platinum electrode surrounded by bromate ions and liquid bromine. Assume that the cell reaction, which produces a positive voltage, involves both chromium(III) and bromate ions. The cell is at 25°C. Information for the bromate reduction half reaction is as follows ... 

Brackets, concentration notation, 151 Brass, 311 Bromate ion, 360 Bromine... 

This subject has been reviewed by Noyes and Field,8 who give reference to the original formulation as well as a more explicit treatment. The presentation here will be given not in general terms but by means of one striking example, the oxidation of malonic acid by bromate ions catalyzed by cerium(IV). It is called the Belousov-Zhabotinsky (or BZ) reaction, after its discoverers.9 The stoichiometry of the reaction with excess malonic acid is... 

A synthetically useful reaction has been reported between alkaline bromine water and dimethyl sulphoxide118, the product being the perbromosulphone (equation 36). A kinetic study of the oxidation of dimethyl sulphoxide by bromate ions, catalysed by ruthenium(III) salts, has also been published but no yield data are available119. 

The products of the reaction between bromide ions and permanganate ions, Mn04, in basic aqueous solution are solid manganese(IV) oxide, MnO>, and bromate ions. Balance the net ionic equation for the reaction. 

The separation in Part a is obvious. Oxidation numbers confirm the other assignments. In Part b, recall that whereas the oxygen atom in H2 O has an oxidation number of-2, the oxygen atoms in H2 O2 have oxidation number -1. In Part c, the oxidation number of the bromine atoms in Br02 is -I3. Among the products, bromine is -H5 in Br03 and -1 in Br. Thus, bromite ions are oxidized to bromate ions in one half-reaction and reduced to bromide ions in the other half-reaction. 

In situ densitometry has been the most preferred method for quantitative analysis of substances. The important applications of densitometry in inorganic PLC include the determination of boron in water and soil samples [38], N03 and FefCNfg in molasses [56], Se in food and biological samples [28,30], rare earths in lanthanum, glass, and monazite sand [22], Mg in aluminum alloys [57], metallic complexes in ground water and electroplating waste water [58], and the bromate ion in bread [59]. TLC in combination with in situ fluorometry has been used for the isolation and determination of zirconium in bauxite and almnimun alloys [34]. The chromatographic system was silica gel as the stationary phase and butanol + methanol + HCl -H water -n HF (30 15 30 10 7) as the mobile phase. 

Another interesting TLC method for the isolation and determination of bromate ion in flour dough and breads has been developed [59]. It involves extraction of BrOj from foodstuff, purification on alumina column, TLC separation on silica gel layer developed with water -1- -butanol + n-propanol (1 1 3), and quantification by densitometry. Bromate ion down to 0.1 pg in bread (1.0 g) was detected with tohdin-FIQ reagent. 

Macalady et al. [ 18] report experiments in which chlorinated sea water was exposed to sunlight at various intensities, to simulate different periods of the day. The results of subsequent analyses for bromates and residual oxidants show that the rate and extent of bromate formation depend on the intensity of the sunlight, with none found in samples kept in the dark for 24 h at 40 °C. It would appear that large amounts of bromate have already been produced in estuarine and coastal waters with unknown effects, as little information is available on the direct toxicity of the bromate ion. 

An acidic bromate solution can oxidize various organic compounds and the reaction is catalyzed by species like cerous and manganous ions that can generate 1-equivalent oxidants with quite positive reduction potential. Belousov (1959) first observed oscillations in Celv]/[Cem] during Ce (III) catalysed oxidation of citric acid by bromate ion. Zhabotinskii made extensive studies of both temporal and spatial oscillations and also demonstrated that instead of Ce (III), weak 1- equivalent reductants like Mn(II) and Fe (II) can also be used. The reaction is called Belousov-Zhabotinskii reaction. This reaction, most studied and best understood, can be represented as... 

E—The bromate ion, Br03, is gaining electrons, so it is being reduced. Reduction always occurs at the cathode. 

Similar results were obtained when carbon was oxidized in liquid medium. Carbon in aqueous suspension is attacked by many oxidizing agents, e.g., permanganate (49-32), chromate (52-54), hypochlorite (52, 55), persulfate (52, 56, 57), and bromate ions (52, 56, 57) chlorine (49), dilute nitric acid (52,58), and concentrated nitric acid (28). The neutralization behavior against the four bases used in Table I was studied with a few samples oxidized in liquid medium (45, 46). The same ratio was observed as with the oxygen-treated carbons, except that twice the amount of groups reacting with sodium bicarbonate was found (Table III). 

In the presence of an oxidant, e.g., chlorate or bromate ions, the electrode reaction is transposed into an adsorption coupled regenerative catalytic mechanism. Figure 2.85 depicts the dependence of the azobenzene net peak current with the concentration of the chlorate ions used as an oxidant. Different curves in Fig. 2.85 correspond to different adsorption strength of the redox couple that is controlled by the content of acetonitrile in the aqueous electrolyte. In most of the cases, parabolic curves have been obtained, in agreement with the theoretically predicted effect for the surface catalytic reaction shown in Fig. 2.81. In a medium containing 50% (v/v) acetonitrile (curve 5 in Fig. 2.85) the current dramatically increases, confirming that moderate adsorption provides the best conditions for analytical application. 

Reaction 12.21 illustrates the trend toward lower electronegativity (less oxidizing power) as one descends a periodic group. The bromine vapor is trapped in aqueous Na2C03 (in effect, a mild source of alkali) as bromide and bromate ions... 

A qualitative similarity to the aqueous chemistry of chlorine will be evident. For each oxoanion of chlorine, there is a corresponding bromine species, although perbromate salts form only under certain strongly oxidizing conditions (e.g., oxidation of bromate ion in alkaline solution with F2 or XeF2) and in fact were unknown until 1968. 

Numerous versions of the Belousov-Zhabotinsky system differ by chemical compounds used. The typical reaction involves oxidation of some organic compound by bromate ion (BrOj ) occurring in acid medium with metal catalyst (Ce3+, Mn2+, as well as complexes of Fe2+, Ru2+). As an example, a particular reaction [4] could be mentioned, where an organic reductor is malonic acid CH2(COOH)2 and Ce3+ ions serve as a catalyst. In this reaction a solution changes periodically its colour due to oscillations in Ce3+ concentration. Generally speaking, the reaction consists of two stages. At the first one metal is oxidized... 

The finely divided metal is soluble in hypohalites if an excess of alkali is present. At red heat, the metal combines with C z to form the dichlondc. Ruthenium(VIIl) oxide is formed when an alkaline ruthenium solution is treated with a strong oxidant, such as chlorine, or bromate ion when the Ru is in acid solution,... 

In the early part of2004 there was a problem in the UK caused by low levels ofbromate in a branded bottled water. This arose from the presence of low levels of bromide in the water that was then disinfected by treatment with ozone. The bromate ions formed were at levels above the EU and EPA limit of lOpg/l for drinking water. The analysis of this anion at trace levels is demanding and should be left to a specialist laboratory. However, Dionex have published four methods that can be used for the analysis of bromate ions in water and the application notes (81, 101, 136 149) are available from the Dionex website (http /www. dionex. com/)... 

PROBLEM 4.21 The concentration of Fe2+ ion in aqueous solution can be determined by redox titration with bromate ion, Br03, according to the net ionic equation... 

The uncatalysed Belousov-Zhabotinsky (B-Z) reaction between malonic acid and acid bromate proceeds by two parallel mechanisms. In one reaction channel the first molecular products are glyoxalic acid and carbon dioxide, whereas in the other channel mesoxalic acid is the first molecular intermediate. The initial reaction for both pathways, for which mechanisms have been suggested, showed first-order dependence on malonic acid and bromate ion.166 The dependence of the maximal rate of the oxidation of hemin with acid bromate has the form v = [hemin]0-8 [Br03 ] [H+]12. Bromate radical, Br02, rather than elemental bromine, is said to play the crucial role. A mechanism has been suggested taking into account the bromate chemistry in B-Z reactions and appropriate steps for hemin. Based on the proposed mechanism, model calculations have been carried out. The results of computation agree with the main experimental features of the reaction.167... 

Water samples Bromine Bromide/bromate Ion exchange/isotopic dilution 6jug I"1 bromide 30/tg I"1 bromate Diemer and Heumann (1997)... 

FIGURE 8.3 Structure of the bromate ion. (From Weigel, D., Imelik, B., and Prettre, M., Bull Soc. Chim. France, 1427, 1962. With permission.)... 

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