Bromine is a chemical element with the symbol Br and an atomic number 35. It is a fuming red-brown liquid at room temperature. Organic bromine compounds are easily dissociated to generate free bromine atoms at high temperatures, which is a process that blocks the free radical chemical chain reactions. This effect makes the organic bromine compounds useful as flame retardants, with more than half of the bromines produced annually in the world are used for this purpose. Bromine compounds are also used in photographic films, and as intermediates in the manufacture of organic chemicals.
Applications
Industrial use: Various organic bromine compounds are used industrially. Some are made from bromine and others are made from hydrogen bromide. Brominated flame retardants have become an increasingly important commodity and constitute the largest commercial use of bromine compounds. When the bromide material burns, the flame retardant generates hydrobromic acid, which interferes with the free radical chain reaction of the fire oxidation reaction. The mechanism is that highly reactive hydrogen radical, the oxygen radical and the hydroxyl radical react with hydrobromic acid to form a less reactive bromine radical, such as a free bromine atom. The bromine atom can also react directly with other radicals to help stop the free radical chain reaction. To prepare brominated polymers and plastics, the bromine-containing compounds can be incorporated into the polymer during the polymerization. One method is to add a relatively small amount of brominated monomer during polymerization. For example, vinyl bromide can be used to produce polyethylene, polyvinyl chloride or polypropylene. It is also possible to add specific highly brominated molecules that participate in the polymerization process. Many gaseous brominated methane compounds are non-toxic and can produce excellent fire suppressant agents through the same mechanism and these fire suppressant agents are particularly effective in enclosed spaces such as submarines and spacecraft.
Chemical use: Bromine compounds are commonly used as intermediates in synthesis of organic compounds. For example, the reaction of flavones with 2,4,4,6-tetrabromocyclohexa-2,5-dienone gives the corresponding 3-bromoflavones under mild reaction conditions. 2,4,4,6-tetrabromocyclohexa-2,5-dienone can produce brominate flavones containing easily oxidized functional groups in dichloromethane at room temperature without harmful oxidation products.
Figure 1. o-Polybromoquinones as brominating agents.
Reference
- Joo, Y. H.; Kim, J. K.; Kang, S.-H. A Convenient Synthesis of 3-Bromoflavones. Synth. Commun. 2002, 32, 1653−1658.
