Hypobromous acid Hypochlorite

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. 

Antimicrobial efficacy is also affected by demand in the cooling water system, specifically demand exerted by ammonia. Chlorine reacts with ammonia to form chloramines, which are not as efficacious as hypochlorous acid or the hypochlorite ion in microbiological control. Bromine reacts with ammonia to form bromamines. Unlike chloramines, bromamines are unstable and reform hypobromous acid. 

Hypobromites, the salts of hypobromous acid, do not keep well because they gradually disproportionate to bromide and bromate. Solutions are best prepared as needed from bromine and alkafl with cooling. Because disproportionation is catalyzed by cobalt, nickel, and copper (70), these impurities should be avoided. SoHd alkaline earth hypobromites, or more properly, bromide hypobromites such as calcium bromide hypobromite [67530-61 CaBr(OBr), have been known for many years, but the pure crystalline hydrates sodium hypobromite pentahydrate [13824-96-9] NaOBr 5H20, and potassium hypobromite tribydrate [13824-97-0], KOBr 3H20, were not described until 1952 (71). Hypobromites are strong bleaching agents, similar to hypochlorites. 

Research has focused on improving the efficiency of the halogenation-oxidation-reduction route by using reagents that perform the halogenation-oxidation in one step. Hypochlorous acid-hypochlorite and hypobromous acid-hypobromite " systems have also been explored for the direct conversion of oximes to a-bromonitroalkanes and a-chloronitroalkanes respectively. Some A-haloheterocycles have been reported to affect direct oxime to a-halonitroalkane conversion, and on some occasions, the use of NBS or the free halogens also leads to a-halonitroalkanes. A mixture of oxone and sodium chloride as a suspension in chloroform is reported as a one-pot method for the direct conversion of oximes to a-chloronitroalkanes. ... 

The reaction of chloro- or bromohydrins with bases provides an economical route for the preparation of epoxides. Halohydrins are readily accessible by treatment of an alkene with either hypochlorous acid (Clj -1- H2O —> HOCl), hypochlorite bleach solution (NaOCl), or hypobromous acid (NBS -1- HjO HOBr). These reactions involve the... 

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. 

The biocidal efficacy of hypobromous acid and hypobromite ion are nearly identical. This is in stark contrast with chlorine where the efficacy of hypochlorite ion is approximately 100 fold less than the acid. 

The product has been used successfully for some fresh water applications. However, in most cases, hypochlorite or hypobromous acid are better choices. At the time this presentation was created, four sold accounts have been obtained for process water application, and a number of trials continue. Based on laboratory and field data, advantages of stabilised hypobromous acid include good persistence, enhanced fouling control, and less aggressiveness towards some papermaking equipment and chemistries. 

Chloramine. By mixing sodium hypochlorite with ammonium bromide, chloramines can be. Chloramines are believed to be nearly as biocidal as hypobromous acid or hypobromite. This product has recently been introduced in. At this time little is known about the product. It requires a somewhat complex feeding system because caustic soda is also added so that the pH can be closely controlled. Furthermore, corrosion problems could be expected on non stainless steel equipment, including in the vapour phase (press and drying sections). 

Hypobromous acid is produced by reacting sodium bromide (21.2.3a.) with hypochlorous acid [HOCl, either from sodium hypochlorite (21.2.2a.) or chlorine (21.2.1.)]. For the generation of HOBr one can proceed as follows 0.55 g of NaBr are mixed with 5 ml of a 5.25% NaOCl solution and diluted to 100 ml with distilled water. At this ratio only HOBr will be produced. 

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