Hypobromous acid, preparation

Preparation. An aqueous solution of hypobromous acid prepared from siiver sulfite and bromine water is shaken with r-butanoi, and the product is extracted with trichlorofluoromethane (Freon 11) and distilled yield 42%. It is a reddish orange liquid with a bromine-like odor and is stable at 0° in the dark for long periods. It is rapidly destroyed at 85° or on irradiation, or by sodium bicarbonate. The reagent reacts with an alkane and bromotrichloromethane to form an alkyl bromide. 

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. 

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. 

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 absolute configuration of (—)-29 was established by X-ray crystal structure analysis of the bromolactone (89), which was prepared from (—)-29 by bromolactonization with hypobromous acid. It was found that ( )-29 belongs to the d series of carba-sugars, and hence, (+)-29 corresponds to the L series. - ... 

A. J. Balard,9 in 1821, also prepared hypobromous acid in a similar manner, namely, by the gradual addition of mercuric oxide of bromine water, and thoroughly shaking the mixture after each addition. Further, quantities of bromine and mercuric oxide can be added until the yellow fluid contains between 6 and 7 parts of HOBr per 100 c.c. The mercuric oxide can be replaced by silver oxide, silver or mercuric nitrate, mercuric acetate, etc. The soln. with 6-7 parts of HOBr per 100 c.c. decomposes at 30°, but more dil. soln. when distilled under ordinary atm. press, give a distillate of bromine followed by a straw-yellow fraction which is a dil. aq. soln. of hypobromous acid. The decomposition is not so pronounced if it be conducted at 40° under a press, of, say, 50 mm. of mercury. 

Bromotoluene has been obtained by the bromination of toluene with bromine in the presence of various catalysts 1 and with hypobromous acid.2 The best method for its preparation, however, is the diazotization of -toluidine followed by replacement of the diazonium group by bromine.3... 

A nitro group may also be introduced by the oxidation of oximes. For this, salts of hypobromous acid are generally used. This method is sometimes applied for the preparation of aliphatic nitro compounds. The reaction proceeds in the following way (Forster [206], Cherkasova and Mehrikov [207], Iffland et al. [208]) ... 

Aliphatic hydrazines of the type RiC(CN)NHNHC(CN)Rj are prepared by the interaction of ketone cyanohydrins and hydrazine. These compounds can be oxidized to azonitriles with hypobromous acid in methanol. In a similar manner, ethyl azodicarboxylate, CjH50jCN=NC0jCiHj, is synthesized by the action of hypochlorous acid on ethyl hydrazodicar-boxylate (83%)- ... 

Similarly, 1% solutions of hypobromous acid may be distilled at atmospheric pressure and 3% solutions may be prepared by distillation under reduced pressure at temperatures below 30°. However, the hypobromous acid tends to decompose during the distillation, due to two simultaneous, but independent side reactions (5 and 6). In the dark at 15 , reaction 5 predominates it is independent of the pH. 

It is practically impossible to prepare a solution of hypobromous acid of known concentration, due to these reactions. 

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... 

In 1908, Kubler, by the action of hypobromous acid on natural con-duritol (32), obtained two bromoquercitols, probably having the configurations dl(134/256) and dl(125/346), (13 and 39). The former isomer should yield the unknown DL-proto-quercitol on dehalogenation the latter isomer (m.p. 196°) was poorly characterized, but it quite possibly was identical with an isomer of m.p. 192° since prepared by Nakajima and Kurihara (see Table III). 

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