Dibromides

Dibromides are chemical compounds that contain two bromine atoms within a single molecule. In organic chemistry the term is commonly applied to dihalides where two bromine substituents are bound to carbon atoms. If both bromines reside on the same carbon, the compound is called a geminal dibromide; if they occupy adjacent carbons, it is a vicinal dibromide. Simple examples include methylene dibromide (CH2Br2), a geminal dibromide, and 1,2-dibromoethane (BrCH2-CH2Br), a vicinal dibromide.

Most vicinal dibromides are prepared by addition of Br2 to alkenes, which gives anti stereochemistry. Geminal dibromides can be prepared from appropriate precursors that install two bromine atoms on one carbon, often as part of multi-step routes in organic synthesis. Other methods may convert aldehydes or other carbonyl-containing substrates into gem-dibromides as part of routes to alkynes.

Reactivity: Dibromides are useful intermediates because they can undergo double dehalogenation to form alkynes. Treatment of vicinal or gem-dibromides with strong bases such as alkoxide or organolithium reagents promotes two successive eliminations, yielding a carbon–carbon triple bond. Dibromides can also be reduced to alkanes in some systems, removing the bromine substituents.

Physical properties vary with structure. Many low-molecular-weight dibromides are colorless liquids or solids with strong odors. Safety concerns are significant: methylene dibromide is toxic and a probable carcinogen; other dibromides may irritate skin and eyes or release brominated byproducts. Appropriate ventilation and protective equipment are recommended when handling these compounds.

Applications include use as synthetic intermediates in organic synthesis, where they enable formation of alkynes or serve as building blocks for complex molecules. Methylene dibromide has historical use as an organic solvent and fumigant but is now restricted in many jurisdictions due to health concerns.