Hydrogenbromid

BeschreibungHydrobromic Acid is a strong acid formed by dissolving the diatomic molecule HBr in water. “Constant-boiling” hydrobromic acid is an aqueous solution that distills at 124.3°C and contains 47.6% HBr by weight. Hydrobromic acid has a pKa of 9, making it a stronger acid than hydrochloric acid, but not as strong as HI, hydroiodic acid. Hydrobromic acid is one of the strongest mineral acids known. Hydrobromic acid is mainly used for the production of inorganic bromides, especially the bromides of zinc, calcium, and sodium. It is a useful reagent for generating organobromine compounds. Certain ethers are cleaved with HBr. It also catalyzes alkylation reactions and the extraction of certain ores. Industrially significant organic compounds prepared from hydrobromic acid include allyl bromide, tetrabromobis(phenol), and bromoacetic acid. Hydrobromic acid can be prepared in the laboratory via the reaction of Br2, SO2 and water. Another laboratory preparation involves the production of anhydrous HBr, which is then dissolved in water. Hydrobromic acid has commonly been prepared industrially by reacting bromine with either sulfur or phosphorous and water. However, it can also be produced electrolytically. It can also be prepared by treating bromides with nonoxidizing acids like phosphoric or acetic acids. Hydrobromic acid is available commercially in various concentrations and purities.

VerwendenHydrogen bromide is used as a reagent and catalyst in several types of organic reactions such as the formation of alkyl bromides from alcohols.It is also used as a source material in the preparation of inorganic bromides. Hydrogen bromide serves as a catalyst in alkylation reactions. It has also been reportedly used in the controlled oxidation of aliphatic and alicyclic hydrocarbons to peroxides, ketones, and acids. In organic synthesis, hydrogen bromide is used to substitute bromine for aliphatic chlorine in the presence of aluminum catalyst.

synthetischeHydrogen bromide gas may be produced by combustion of hydrogen inbromine vapor at 37.5°C using a catalyst such as platinized asbestos or pla-tinized silica gel. Unreacted free bromine is removed from the product bypassing the gaseous product mixture over hot activated charcoal. Hydrogenbromide formed may be absorbed in water to obtain the acid; or may be cooledand liquefied for shipment in cylinders. Hydrobromic acid may be prepared in the laboratory by distillation of asolution of potassium bromide with dilute sulfuric acid: 2KBr + H2SO4 → K2SO4 + HBr The acid may be prepared by several other methods, as well, including reac-tion of bromine either with sulfur and water; or with phosphorus and water: 2Br2 + S + 2H2O → 4HBr + SO2 Hydrobromic acid also may be prepared by hydrogen exchange with a sodiumor potassium bromide solution when the solution is passed through a cation-exchange resin. Hydrobromic acid is stored and shipped in drums, tanks, carboys, or bot-tles, labeled as corrosive materials. The anhydrous gas is stored and shippedin cylinders under its vapor pressure.