Oxidation of bromide

In the laboratory, bromine is prepared by oxidation of bromide ion the oxidation is carried out by mixing solid potassium bromide with manganese(IV) oxide and distilling with concentrated sulphuric acid ... 

Sanitizers. Spa and hot-tub sanitation is dominated by chlorine- and bromine-based disinfectants. Public spas and tubs usually employ automatic feeders, eg, CI2 gas feeders, to maintain a disinfectant residual. Private or residential spas and tubs can use automatic chemical feeding or generating devices, or they can be sanitized manually with granular or liquid products. The most widely used products for private spa and tub sanitation are sodium dichloroisocyanurate and bromochlorodimethylhydantoin. Granular products are normally added before and after use, whereas solids, eg, stick-bromine, are placed in skimmers or feeders. Bromine generating systems can also be used and are based on oxidation of bromide ions (added to the water as sodium bromide) by peroxymonosulfate, chloroisocyanurates, hypochlorites, or ozone to generate the disinfectant HOBr. 

There are four principal steps in bromine production (/) oxidation of bromide to bromine (2) stripping bromine from the aqueous solution (3) separation of bromine from the vapor and (4) purification of the bromine. Most of the differences between the various bromine manufacturing processes are in the stripping step. 

Boiling the solution speeds the conversion of intermediate hypobromites and bromites to bromate. The less soluble bromate can be separated from the hahde by fractional crystallization. A method that is often more economical is the oxidation of bromides into bromates by hypochlorites in aqueous solution. This can be done by passing chlorine into an alkaline bromide solution (75) ... 

Recovery Process. Commercial processes depend on the oxidation of bromide to bromine. Most of the Hberated bromine remains dissolved in the brine. The brine is then stripped of bromine followed by recovery of bromine from the stripping agent. Subsequent purification by distillation is often a final step. 

Two approaches that have been investigated recently for disinfection are mixtures of bromine and chlorine, and mixtures containing bromide or iodide salts. Some evidence exists that mixtures of bromine and chlorine have superior germicidal properties than either halogen alone. It is believed that the increased bacterial activity of these mixtures can be attributed to the attacks by bromine on sites other than those affected by chlorine. The oxidation of bromide or iodide salts can be used to prepare interhalogen compounds or the hypollalous acid in accordance with the following reaction ... 

Such solutions are necessarily contaminated with halide ions and with the products of any subsequent decomposition of the hypohalite anions themselves. Alternative routes are the electrochemical oxidation of halides in cold dilute solutions or the chemical oxidation of bromides and iodides ... 

Discussion. Bromine may be electro-generated with 100 per cent current efficiency by the oxidation of bromide ion at a platinum anode. Bromination of oxine proceeds according to the equation ... 

We can often recognize loss of electrons by noting the increase in the charge of a species. This rule also applies to anions, as in the oxidation of bromide ions (charge —1) to bromine (charge 0) in a reaction such as the one used commercially to make bromine (Fig. K.2) ... 

In the presence of bromide ion the slow one-electron transfer oxidation of the ArCH3 substrate is replaced by the rapid one-electron oxidation of bromide ion by cobalt(III) to afford a bromine atom. The latter, or rather its adduct with bromide ion, Br2 acts as the chain transfer agent in the reaction with the ArCH3 substrate (Fig. 10). 

However, just as real reactions do not include free electrons as reactants or products, they do not occur between or produce materials with (substantive) net charges. So whilst the equation above does represent the oxidation of bromide by acidified permanganate, it is an abstraction from a real chemical reaction where the bromide and the permanganate would be part of real substances that were (substantially) neutral. For example ... 

The oxidation of bromide ion by Cr(VI) has been examined at length by Bobtelsky et The rate equation is... 

Dhar noted that the oxidation of oxalic acid by chromic acid is markedly accelerated on adding manganous ions, the reaction order in Cr(VI) changing from one to zero. Bobtelsky and Glasner ° found the oxidation of bromide ions by chromic acid in aqueous sulphuric acid to follow kinetics... 

The reactive species might be V(OH)2l, produced in a similar manner to the analogous species in the oxidation of bromide ion, which could undergo one-equivalent breakdown to V(IV) and atomic iodine. Ramsey et al postulate transfer of OH to iodide ion, but the intermediacy of-12 is referred to in a later study of the oxygen effect to account for the relation ... 

Figure 1 The microbial fouling process on surfaces of certain macroalgae in aquatic environments is controlled by the selective oxidation of bromide with hydrogen peroxide and bromoperoxidase. Although chloride is many orders of magnitude more abundant in the sea, bromide is oxidized to hypobromous acid in situ.

Figure 4 Stabilized bromine antimicrobials are produced by eosinophils, a type of mammalian white blood cell. Bacteria are captured by phagocytosis and contained intracellularly within vesicles called phagosomes. Granules release cationic surfactants, lytic enzymes, and eosinophil peroxidase into the phagosome in a process known as degranulation. Eosinophil peroxidase, an enzyme that is structurally similar to the bromoperoxidases found in seaweed (Figure I), selectively catalyzes oxidation of bromide to hypobromite by reducing hydrogen peroxide to water. The hypobromite immediately reacts with nitrogenous stabilizers such as aminoethanesulfonic acid (taurine) to form more effective and less toxic antimicrobial agents.

Typically, oxidation of bromide generates only small measured currents. However, if it is assumed that all the current passes through the active sites within an area of approximately 500 nm diameter, the current density at the active regions would be very large indeed and on the order of 1 A/cm. Thus, the oxidation of bromide is associated with an intense but highly localized current. 

Write a balanced half-reaction for the oxidation of bromide ions to bromine. 

There are two possible oxidation half-reactions at the anode the oxidation of bromide ion in the electrolyte, or the oxidation of water. 

The transfer of bromine across liquid-liquid and gas-liquid interfaces is of considerable interest, for example, for sensor systems or for fundamental insights in the effects of bromine in the environment. A new methodology for kinetic studies at a lipid layer has been reported by Zhang etal. ]138]. A microelectrode immersed in the aqueous phase is placed in close distance to a lipid surface layer in contact with a gas phase. The oxidation of bromide at the electrode causes the formation of bromine, which in part escapes through the lipid layer into the gas phase (see Scheme 4). 

In the oxidation of bromide by thallic ions a double electron transfer from the central atom to two separate ligands was postulated 27)... 

It is possible to use this OH° concentration to predict k for the oxidation of other compounds under the same conditions. Von Gunten et al. (1995) calculated the actual concentration of OH° using this general and easy way for the ozonation of surface water at neutral pH in a two-stage pilot plant. Atrazine was used as the model compound, ozone decay was assumed to be of first order and the reactors completely mixed. Based on this model they were able to precisely predict the formation of bromate (Br03 ) by oxidation of bromide (Br ) for a full-scale water treatment plant. Bromate is a disinfection byproduct (DBP) of the ozonation of bromide-containing waters, and of concern because of its carcinogenic effects in animal experiments (see also Chapter A 3). 

Clague MJ, Keder NL, Butler A (1993) Biomimics of Vanadium Bromoperoxidase Vanadium(V)-Schiff Base Catalyzed Oxidation of Bromide by Hydrogen Peroxide. Inorg Chem 32 4754... 

Clague MJ, Butler A (1995) On the Mechanism of < 7 v- Dioxovanad ium(V)-Catalyzed Oxidation of Bromide by Hydrogen Peroxide Evidence for a Reactive, Binuclear Vanadi-um(V) Peroxo Complex. J Am Chem Soc 117 3475... 

In addition to the direct conversions shown above, electrochemistry is often used in an indirect fashion, e.g. for the in situ generation of (harmful) reagents such as bromine or iodine by oxidation of bromide and iodide ion, respectively, or of Ce4+ by oxidation of Ce3+ [28]. Also, the regeneration of oxidation products such as dichromate, Equations 6.1a and 6.3, has been put to use [28] ... 

In addition to bromide and iodide, V-BrPO can catalyze the oxidation of chloride [64]. As mentioned previously and discussed more fully later, a distinct enzyme, vanadium chloroperoxidase, has also been discovered. Originally it was thought that V-BrPO could only catalyze the oxidation of bromide and iodide by dihydrogen peroxide. In fact, under the standard mcd bromoperoxidase assay conditions, in which the V-BrPO concentration is ca. nanomolar, very little, if any, chlorination of mcd is observed. However, it seemed very unusual that V-BrPO could be inhibited by fluoride and bromide, but apparently not by chloride [27], In reinvestigating the halide specificity of V-BrPO, it was discovered that when the enzyme concentration is increased 100-fold to 0.1 pM, chlorination is observed at an appreciable rate [64], The specific chloroperoxidase activity is 0.76 U/mg (under conditions of 1 M certified 100% bromide-free KC1, 2 mMH202, 50 pM... 

The equilibrium constant for coordination of the first equivalent of H202 to V02+ is 3.7 X 104 M l and is independent of pH [75], The binding constant for the second equivalent of H202 is 0.6 M and depends on pH with significantly less peroxide coordination at higher acid concentration [63], Since the publication of the first edition of Bioinorganic Catalysis, the specific oxidant of bromide has been identified ... 

Other groups have also examined vanadium(V) catalyzed oxidation of bromide by dihydrogen peroxide in acidic aqueous or aqueous/organic mixtures, although without examining the detailed speciation of the vanadium peroxo compounds in solution [77-82], These reports have focused more on the nature of the substrate brominated and the product distribution under different conditions. 

Table 2 Second-Order Rate Constant for the Oxidation of Bromide by Peroxo Metal Species...

The noncomplementary oxidation of bromide by Mn(III) acetate in acetic acid is second order with respect to HBr. The overall third-order rate constant kMn is (4.10 0.08) x 105 M 2 s 1 at 4.5°C in 10% aqueous acetic acid.21... 

---