Acid, hypobromous

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. 

In the olivanic acid series of carbapenems the ( )-acetamidoethenyl grouping can be isomerised to the (Z)-isomer (19) (22) and reaction with hypobromous acid provides a bromohydrin that fragments to give a thiol of type (20) when R = H, SO H, or COCH. The thiol is not isolated but can react to provide new alkyl or alkenyl C-2 substituents (28). In the case of the nonsulfated olivanic acids, inversion of the stereochemistry at the 8(3)-hydroxyl group by way of a Mitsunobu reaction affords an entry to the 8(R)-thienamycin series (29). An alternative method for introducing new sulfur substituents makes use of a displacement reaction of a carbapenem (3)-oxide with a thiol (30). Microbial deacylation of the acylamino group in PS-5 (5) has... 

Bromine reacts with essentially all metals, except tantalum and niobium, although elevated temperatures are sometimes required, eg, soHd sodium does not react with dry bromine but sodium vapor reacts vigorously. Metals such as lead, magnesium, nickel, and silver react with bromine to form a surface coat of bromide that resists further attack. This protective coating allows lead and nickel to be used as linings in bromine containers. Metals tend to be corroded by bromine faster in the presence of moisture than without, probably because of the formation of hydrobromic and hypobromous acids. 

The equihbrium constant for this reaction at 25°C is 7.2 x 10 Af (22). Light catalyzes the decomposition of hypobromous acid to hydrogen bromide and oxygen. 

In the dark, hypobromous acid decomposes to bromic acid and bromine. Bromic acid is relatively unstable and decomposes slowly to give bromine and oxygen. 

In the blowing-out process, used when the source of bromine is seawater, air is used instead of steam to strip bromine from solution. At the pH of seawater the Hberated bromine hydroly2es to hypobromous acid and bromide. Bromide traps bromine as the tribromide ion and Htde bromine is released. Before stripping, enough sulfuric acid is added to the seawater to reduce the pH to 3—3.5. 

Acids nd Sa.lts. The oxygen acids of bromine are strong oxidants but at ordinary temperatures are stable only in solution. An aqueous solution of hypobromous acid [13517-11-8] may be prepared by treating bromine water with silver oxide or mercuric oxide (69) ... 

A more concentrated solution of HOBr can be prepared by filtration of one of the above solutions and distillation in vacuum. Or the mercuric oxide reaction can be carried out in Freon 11 without water, yielding a solution of bromine monoxide which is filtered and hydrolyzed. Hypobromous acid is slightly ionized its dissociation constant at 25°C is 2 x 10 . ... 

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. 

Some nitrate is also formed, thus the HOCl/NH stoichiometry is greater than theoretical, ie, - 1.7. This reaction, commonly called breakpoint chlorination, involves intermediate formation of unstable dichloramine and has been modeled kinetically (28). Hypobromous acid also oxidizes ammonia via the breakpoint reaction (29). The reaction is virtually quantitative in the presence of excess HOBr. In the case of chlorine, Htde or no decomposition of NH occurs until essentially complete conversion to monochloramine. In contrast, oxidation of NH commences immediately with HOBr because equihbrium concentrations of NH2Br and NHBr2 are formed initially. As a result, the typical hump in the breakpoint curve is much lower than in the case of chlorine. 

Addition to the Double Bond. Chlorine, bromine, and iodine react with aHyl chloride at temperatures below the inception of the substitution reaction to produce the 1,2,3-trihaLides. High temperature halogenation by a free-radical mechanism leads to unsaturated dihalides CH2=CHCHC1X. Hypochlorous and hypobromous acids add to form glycerol dihalohydrins, principally the 2,3-dihalo isomer. Dehydrohalogenation with alkah to epicbl orobydrin [106-89-8] is ofgreat industrial importance. 

Ethylene bromohydrin has been prepared by the reaction between ethylene glycol and hydrobromic acid and phosphorus tribromide. It has also been prepared by the direct addition of hypobromous acid to ethylene, and by the reaction between ethylene and dilute bromine water. With ethylene oxide now available at a reasonable price, the method described is probably the best because of the high yields and the convenience of reaction. 

Bromination can also be carried out using solutions of acetyl hypobromite or trifluoroacetyl hypobromite. Acetyl hypobromite is considered to be the active halogen-ating species in solutions of hypobromous acid in acetic acid ... 

Since hypohalous acid is a much more active disinfectant than the hypohalite ion, the effect of pH on ionization becomes important. Hypobromous acid has a lower ionization value than hypochlorous acid and this contributes to the higher disinfectant activity of BrCl compared with chlorine. 

The mechanism of oxidation has not been studied in detail. In aqueous media it may be assumed that hypobromous acid is formed and that this is the true oxidizing agent. Indeed, Deno" has shown that the rate of oxidation of alcohols by aqueous bromine closely parallels the HOBr concentration and that the alkyl hypohalide is a most likely intermediate. Rate studies and... 

Bromination with A-bromosuccinimide generally gives the same result as bromination with free bromine or hypobromous acid. The reaction is considered to proceed with a small concentration of free bromine and does not generate an appreciable concentration of acid. Conditions are therefore mild. In addition, A-bromosuccinimide has been used to brominate the allylic position of a, -unsaturated ketones in the presence of free-radical promoters or with irradiation, and thus gives access to dienones by dehydro-halogenation, for exaraple " ... 

The method of Fried and Sabo for the in situ preparation of hypobromous acid from A-bromoacetamide (or A-bromosuccinimide) in aqueous dioxane or acetone containing perchloric acid is commonly used, e.g., (81) (82). 

The Addition of Hypobromous Acid HOBr) to Steroid Olefins... 

While an aromatic A-ring does not interfere with this sequence, isolated double bonds will react with hypobromous acid. 

Carboxylic acid, 161, also serves as starting material for a substituted pyrazine that has proven to be an important diuretic agent. As the first step in the synthesis the acid is converted to the corresponding amide (165). Treatment with a single equivalent of hypobromous acid effects Hoffmann rearrangement of only one of the amide groups. Ethanolysis of the intermediate carbamate leads directly to the amino ester (166). Exposure of the... 

More recent work in the corticosteroid senes has involved modification of the dihydrox-yacetone side chain at the 17 position Activity is retained, for example, when the hydroxyl group at the 17 position is omitted Thus, addition of the elements of hypobromous acid to tnene 36 [8], gives the bromohydnn 37, treatment with base leads to internal elimination to form the p-epoxide 38, opening of the oxir.ine with hydrogen fluoride gives desoximetasone, 39, [9]... 

Derbyshire and Waters192 measured the rates of bromination of sodium toluene-m-sulphonate (in water) and of benzoic acid (in aqueous acetic acid) by hypobromous acid with sulphuric or perchloric acids as catalysts, all at 21.5 °C. No bromination occurred in the absence of mineral acid and the reaction was strictly first-order in aromatic and in hypobromous acid. The function of the catalyst was considered to be the formation of a positive brominating species, according to the equilibrium... 

The positive bromination of aromatics ethers was first studied by Bradfield et al.193 and by Branch and Jones194. The reaction of hypobromous acid in 75 % aqueous acetic acid with benzyl 4-nitrophenyl ether and 4-nitrophenetole at 20 °C was very rapid and approximately second-order193. The value of k2/[H+] remained constant in the [H+] range 0.005-0.090 M for the effect of added mineral acids on the bromination of 4-nitroanisole and 4-nitrophenetole (at 19.8 °C)194. The variation in reaction rate with the percentage of acetic acid in the medium was also studied and showed a large increase in the 0-10 % range with a levelling off at approximately 25 % acetic acid (Table 52) this was attributed... 

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