Dibromomethane or methylene bromide, or methylene dibromide is a halomethane with the formula CH<sub>2</sub>Br<sub>2</sub>. It is slightly soluble in water but very soluble in organic solvents. It is a colorless liquid.
At ambient temperature, dibromomethane solidifies around 0.61 GPa. The crystal structure strongly suggests both interhalogen and hydrogen-halogen interactions.
Dibromomethane is prepared commercially from dichloromethane via bromochloromethane:
The latter route requires aluminium trichloride as a catalyst. The bromochloromethane product from either reaction can further react in a similar manner:
In the laboratory, it is prepared from bromoform using sodium arsenite and sodium hydroxide:
Another way is to prepare it from diiodomethane and bromine.
Dibromomethane is used as a solvent, gauge fluid, and in organic synthesis (often as <sup>1</sup>H-NMR internal standard). It conviently converts polyols (such as catechols) to their methylenedioxy derivatives, and bromomethylenates enolates. It is a much cheaper precursor to a Simmons-Smith-type reagent than diiodomethane.
It is naturally produced by marine algae and liberated to the oceans. Releasing on soil causes it to evaporate and leach into the ground. Releasing in water causes it to be lost mainly by volatilisation with a half life of 5.2 hours. It has no significant degradation biological or abiological effects. In the atmosphere it will be lost because of reaction with photochemically produced hydroxyl radicals. The estimated half life of this reaction is 213 days.