Bromination and hydrobromic acid

Bromo-pentammino-rhodium Bromide, [Rh(NH3)5Br]Br2, is prepared in a similar manner to the cliloro-salt by heating rhodium-zinc alloy with a mixture of bromine and hydrobromic acid, or by warming aquo-pentammino-rhodium bromide with excess of hydrobromic acid to 100° C.1 2 It separates in small orthorhombic yellow crystals which are almost insoluble in cold water and insoluble in alcohol and hydrobromic acid. It has the same constitution as the ehloro-compound. Treated with nitric acid, hydrochloric acid, or silver carbonate, it yields the corresponding salts respectively, and with moist silver oxide yields an unstable hydroxide, [Rh(NIT3)5Br](OH)2. The methods from the preparation of the bromo-salts are like those for the ehloro-salts. 

The necessity of introducing the bromine at the bottom of the mixture should be emphasized. If this is not done, local overheating is almost certain to occur, with consequent loss of both bromine and hydrobromic acid. 

A more satisfactory method consists in dissolving platinum sponge in hydrobromic acid saturated with bromine. This may be effected in a sealed glass tube at 180° C., but that is not necessary. If the platinum sponge is simply boiled for a short time with an excess of bromine and hydrobromic acid in a flask with a reflux condenser, the whole is dissolved,8 yielding a solution of brom-platinic acid. 

Bromine and hydrobromic acid at 100°, extraordinarily, seem to cleave the 21,22-double bond in compounds in which the benzene ring... 

Thiols are also useful sources of the corresponding bromo compounds, by reaction with bromine and hydrobromic acid." Alkylthio substituents can be displaced by the usual range of nucleophiles, but the corresponding sulfones are more reactive. " ... 

The Karlsruhe Research Centre in Germany has foimd that bromine and hydrobromic acid can be recovered from post-consumer electrical and electronic waste containing brominated flame retardants. Incineration of mixed waste containing high percentages of similar products did not cause a significant increase in dioxin production. 

Methyl bromide slowly hydrolyzes in water, forming methanol and hydrobromic acid. The bromine atom of methyl bromide is an excellent leaving group in nucleophilic substitution reactions and is displaced by a variety of nucleophiles. Thus methyl bromide is useful in a variety of methylation reactions, such as the syntheses of ethers, sulfides, esters, and amines. Tertiary amines are methylated by methyl bromide to form quaternary ammonium bromides, some of which are active as microbicides. 

Orotic acid undergoes 5-nitration, 5-bromination in hydrobromic acid with peroxide, 5,5-dibromination following decarboxylation in bromine water, esterification, methylation (rather complicated), conversion into its acid chloride (containing some anhydride) by treatment with thionyl chloride, and conversion into 2,6-dichloropyrimidine-4-carboxylic acid by phosphoryl chloride (62HC(16)422). 

Excess of bromine converts each methylpteridine compound into the dibromomethyl derivative which on hydrolysis gives good yields of the corresponding aldehyde. An interesting variation of the reaction conditions was found in the treatment of the C- methylpteridines with POBra, which leads to the same mono- and di-bromomethyl derivatives. 6-Methylpterin reacts with more difficulty and with an excess of bromine in hydrobromic acid forms the... 

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. 

Plants producing and handling halogens and halogen compounds Tantalum finds extensive use in the production and handling of hydrochloric and hydrobromic acid, chlorine and bromine and many of their derivatives. Absorbers, coolers and heaters which show considerable advantages in terms of heat-flux capabilities and corrosion resistance have been used on hydrochloric acid duties for over 40 years and condensers have been used in bromine plants for at least the same period. Typical applications of tantalum in the bromine and chlorine industries are listed in Table 5.27 . 

Benzofurazan (benz-1,2,5-oxadiazole) reacted with bromine by addition to give a4,5,6,7-tetrabromo adduct. Bromine in hydrobromic acid solution 4-brominated both 5-methyl- and 5-bromo-benzofurazans (74JHC8I3). When 4,7-dinitrobenzofurazan was treated with ammonium chloride in refluxing acetic acid, nucleophilic displacement gave rise to the 4-chloro-7-nitro derivative (83URP1004375). Naphtho[l, 2-c]furazans (42) are mainly 4-halogenated, but there is minor substitution in the 8-position (73CHE1331). 

As illustrated in Figure 12, the reaction mixture contains mono-, di-, and tri-brominated glycols, hydrobromic acid, and water. The mixture is extremely corrosive, and the reactor is operated at a temperature just above the freezing point of the product. The key to successfully sampling this mixture was the use of a corrosion-resistant tantalum sampling system. In addition, the sample line was continuously flushed with reactor solvent except during sampling. 

Ispra Mark 13A A flue-gas desulfurization process developed at the Joint Research Centre of the European Community at Ispra, Italy, from 1979. It uses a novel electrochemical method to regenerate the solution used for absorbing the sulfur dioxide. The products are concentrated sulfuric acid and hydrogen. The absorbent is a dilute aqueous solution of sulfuric and hydrobromic acids, containing a small amount of elemental bromine. Sulfur dioxide reacts with the bromine thus ... 

The methods for the preparation of bromotrimethylsilane include the treatment of hexamethyldisiloxane with bromine reagents such as phosphorus tribromide,1,2 2,2,2-tribromo-l, 3,2 /5-benzodioxaphosphole (catechyl phosphorus tribromide),2 and aluminium tribromide,3 the yields being in the range from 73 to 87%. A further method4 shows that bromotrimethylsilane can be obtained from aminosilanes and hydrobromic acid, but the yield (55%) is lower than in the former methods. Other methods involve the use of expensive reagents, such as hexamethyldisilane, l,4-bis(trimethylsilyl)-2, 5-cyclohexadiene, and 1,4-dihydro-l, 4-bis(trimethylsilyl)naphthalene.5 Finally, some alternative procedures have been developed for its in situ preparation.5... 

Chemical PropeHies.—Arsenic tribromide reacts with water in small quantity to form the oxybromide, AsOBr in larger quantity arsenious and hydrobromic acids are formed.8 One part of the tribromide dissolves in three parts of boiling water,9 and on cooling the solution deposits crystals of arsenious oxide. The tribromide is less soluble in aqueous hydrobromic acid. It dissolves in bromine, but does not combine... 

Two hundred grams of freshly distilled dry n-caproic acid is placed in a i-l. flask with 300 g. of bromine which has been dried by washing once with 200 cc. of concentrated sulfuric acid (Note 1). A 3-cc. portion of phosphorus trichloride is cautiously added and the flask connected to a reflux condenser (Note 2), the top of which is connected with a trap and absorption bottle containing water. The mixture is then heated in a water or oil bath to 65-70°, at which temperature the reaction commences and hydrobromic acid is given off smoothly. After five to six hours, the bromine has all reacted (Note 3). Towards the end of the reaction, the temperature is allowed to rise to about ioo°. The contents of the flask are now distilled under diminished pressure (Note 4). The fraction boiling at 132-i40°/i5 mm. is collected and amounts to 280-298 g. (81-89 per cent of the theoretical amount). 

An aqueous solution of the substance is mixed with a solution of bromine in hydrobromic acid or potassium bromide, when a reddish-brown oil separates. This solidifies to a mass of leafy crystals, if the aqueous layer is poured off the oil, and the latter washed with a little ether. The crystals are diazobenzene perbromide. 

---