Hypobromite ion

Cooling water pH affects oxidizing antimicrobial efficacy. The pH determines the relative proportions of hypochlorous acid and hypochlorite ion or, in systems treated with bromine donors, hypobromous acid and hypobromite ion. The acid forms of the halogens are usually more effective antimicrobials than the dissociated forms. Under some conditions, hypochlorous acid is 80 times more effective in controlling bacteria than the hypochlorite ion. Hypochlorous acid predominates below a pH of 7.6. Hypobromous acid predominates below pH 8.7, making bromine donors more effective than chlorine donors in alkaline cooling waters, especially where contact time is limited. 

Another reaction that can be used for conversion of carboxylic acids to the corresponding amines with loss of carbon dioxide is the Hofmann rearrangement. The classic reagent is hypobromite ion, which reacts to form an A-bromoamide intermediate. Like the Curtius reaction, this rearrangement is believed to be a concerted process and proceeds through an isocyanate intermediate. 

Methyl ketones are degraded to the next lower carboxylic acid by reaction with hypochlorite or hypobromite ions. The initial step in these reactions involves base-catalyzed halogenation. The a-haloketones are more reactive than their precursors, and rapid halogenation to the trihalo compound results. Trihalomethyl ketones are susceptible to alkaline cleavage because of the inductive stabilization provided by the halogen atoms. 

Chlorinated waters are being discharged to estuaries and coastal waters in increasing quantities. In such systems the chlorine reacts with the natural bromide and ammonia at pH 8 to produce the highly toxic hypobromous acid, hypobromite ion, and haloamines. For normal seawater of pH 8, the initial products of chlorination are a mixture of hypobromous acid and the hypobromite ion. Both of these compounds are unstable with respect to decomposition and disproportionation. 

The names are bromide ion, bromate ion, bromite ion, hypobromite ion, and perbromate ion. 

Chlorine is applied as chlorine gas, powdered calcium hypochlorite (Ca(OCl)2), or liquid sodium hypochlorite (NaOCl bleach). Chlorine reacts with the organic (natural organic matter, NOM) or inorganic (bromide ion, Br ) precursors in the water to form chlorine disinfection by-products (CBPs), including trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), haloketones, chloral hydrate, and chloropicrin. Humic and fulvic acids are the predominant NOMs. When bromine exists, the chlorine oxidizes it to hypobromous acid/ hypobromite ion (HOBr/OBr ) to form bromo THMs (bromodichloromethane, BDCM, and di-bromochloromethane, DBCM), HAAs, and HANs. 

Calculate the equihbrium constant for the reaction of hypobromite ions (OBr ) with water. 

If bromide ion is present in the water being treated with ozone, it is quickly oxidised to hypobromite ion and hypobromous acid (see earlier in this section). The hypobromous acid probably contributes to the biocide effect under these circumstances. The unique chemistry of ozone and bromide is discussed later. 

Rice and Wilkes [1991] have discussed the unique chemistry of ozone and bromide ion. Their observations are of interest where bromide ions exist in cooling water for instance, in sea water. Ozone reacts rapidly with bromide ion to produce hypobromite ion, i.e. 

Hypobromite ion can be further oxidised with additional ozone to bromate ion... 

In the presence of the oxidizing agent the hypobromite ion, hydrazobenzene is oxidized to azobenzene. The reaction can be balanced by inspection, using one H2O molecule... 

The possible oxidizing species in alkaline BAB solutions are PhS02NBr PhS02NHBr, HOBr and OBrHardy and Johnston s calculations[7] on alkaline bromamine-B solutions indicated that there could be considerable concentration of PhS02NHBr even in alkaline medium. Further as the concentration of alkali increases, there is also increase in the concentration of hypobromite ion. Hence, in the present investigations, a fractional order dependence on [substrate] and [OH and tbe observed retardation of rate by the reaction product (PhS02NH2) can be explained by tbe two pathway mechanism shown in schemes 1 and 2 ... 

Calculate the molar concentration of OH" solution of hypobromite ion (BrO K , What is the pH of this solution ... 

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