Bromine

Abstract

Bromine, Br 2 , is the only nonmetallic element that is a liquid at standard conditions. Bromine, Br, has at no. 35, at wt 79.904, and belongs to Group 17 (VIIA) of the Periodic Table, the halogens. Its electronic configuration is (1 s ) 2 (2 s ) 2 (2 p ) 6 (3 s ) 2 (3 p ) 6 (3 d ) 10 (4 s ) 2 (4 p ) 5 . The element's known isotopes range in mass number from 74 to 90. Isotopes usable as radioactive tracers are 77, 80, 80m (metastable), and 82. Bromine has two stable isotopes, 79 Br and 81 Br. The most common valence states are \documentclass{article}\pagestyle{empty}\begin{document}${-1}$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}${+5}$\end{document} , but \documentclass{article}\pagestyle{empty}\begin{document}${+1}$\end{document} , \documentclass{article}\pagestyle{empty}\begin{document}${+3}$\end{document} , and \documentclass{article}\pagestyle{empty}\begin{document}${+7}$\end{document} are also observed. Bromine is a dense, dark red, mobile liquid that vaporizes readily at room temperature to give a red vapor that is highly corrosive to many materials and human tissues. Bromine liquid and vapor, up to about 600°C, are diatomic (Br 2 ). Bromine is moderately soluble in water, 33.6 g/L at 25°C. Bromine is soluble in nonpolar solvents and in certain polar solvents such as alcohol and sulfuric acid. Bromine cam function as a solvent. One of the central features of the chemistry of bromine, and the other halogens, is the tendency to acquire an electron to form either a negative ion, \documentclass{article}\pagestyle{empty}\begin{document}${{\rm{X}}{^{-}}}$\end{document} , or a single covalent bond, \documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document}${{\relbar \kern-5pt{\relbar}\kern-7pt{\relbar}}{\rm{X}}}$\end{document} . Bromine combines directly with hydrogen at elevated temperatures and this is the basis for the commercial production of hydrogen bromide. Bromine reacts with essentially all metals, except tantalum and niobium, although elevated temperatures are sometimes required. Bromide ion is oxidized by chlorine to bromine. This is the basic reaction in the production of bromine from seawater, brines, or bitterns. Bromine oxidizes sulfur and a number of its compounds. Bromine also oxidizes red phosphorus and some phosphorus compounds. Ammonia, hydrazine, nitrites, and azides are oxidized by bromine. Bromine oxidizes carbon and reacts with carbon monoxide to form carbonyl bromide. The addition of bromine to unsaturated carbon compounds occurs readily. In the presence of halogen Lewis acids, such as metal halides or iodine, aromatic hydrocarbons are halogenated on the ring. Phenols and phenol ethers readily undergo mono‐, di‐, or tribromination in inert solvents depending on the amount of bromine used. Heterocyclic compounds range from those such as furan, which is readily halogenated and tends to give polyhalogenated products, to pyridine, which forms a complex with aluminum chloride that can only be brominated to 50% reaction. Acids and esters are less easily brominated than aldehydes or ketones. Organometallic compounds can react with bromine to give bromides, but because organometallic compounds are frequently made from bromides the reaction with iodine to give iodides is of more synthetic significance. Bromine is widely distributed in nature but in relatively small amounts. Bromine occurs in the form of bromide in seawater and in natural brine deposits. Chloride is also present. In all current methods of bromine production, chlorine is used to oxidize bromide to bromine. There are four principal steps in bromine production: oxidation of bromide to bromine; stripping bromine from the aqueous solution; separation of bromine from the vapor; and purification of the bromine. Facilities for manufacturing bromine are primarily located near sources of natural brines or bitterns containing usable levels of bromine. Bromine has a sharp, penetrating odor. The OSHA/ACGIH threshold limit value–time‐weighted average for an 8‐h workday and 40‐h workweek is 0.1 ppm in air. Symptoms of overexposure include coughing, nose bleed, feeling of oppression, dizziness, headache, and possibly delayed abdominal pain and diarrhea. Pneumonia may be a late complication of severe exposure. Liquid bromine produces a mild cooling sensation on first contact with the skin. This is followed by a sensation of heat. If bromine is not removed immediately by flooding with water, the skin becomes red and finally brown, resulting in a deep burn that heals slowly. Bromine is especially hazardous to the tissues of the eyes where severely painful and destructive burns may result from contact with either liquid or concentrated vapor. Ingestion causes severe burns to the gastrointestinal tract. For handling bromine in the laboratory the minimum safety equipment should include chemical goggles, rubber gloves (Buna‐ N or neoprene rubber), laboratory coat, and fume hood. For handling bromine in a plant, safety equipment should include hard hat, goggles, neoprene full‐coverage slicker, Buna‐ N or neoprene rubber gloves, and neoprene boots. Bromine is nonflammable but may ignite combustibles such as dry grass, on contact. Bromine should be stored in a cool, dry area away from heat. Under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA)/RCRA regulations in effect at the end of 1986 bromine is regulated as a hazardous waste or material and must be disposed of in an approved hazardous waste facility in compliance with EPA or other applicable local, state, and federal regulations. Glass, lead, tantalum, niobium, nickel, and the fluoropolymers Kynar, Halar, and Teflon are highly resistant to bromine. An important use of bromine compounds is in the production of flame retardants. Bromine‐containing epoxy sealants are used in semiconductor devices. Bromine has some use in swimming pools and in bleaching; it is also a disinfectant for cooling water and wastewater. Its main use is as a chemical reactant.