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Dibromomethane

| NFPA-H = 2 | NFPA-F = 0 | NFPA-R = 0 | 1 g⋅kg−1 (oral, rabbit) | 3.738 g⋅kg−1 (subcutaneous, mouse) | 4 g⋅kg−1 (dermal, rabbit) | Bromoform | Tetrabromomethane | 1,1-Dibromoethane | 1,2-Dibromoethane}} Dibromomethane or methylene bromide, or methylene dibromide is a halomethane with the formula CH2Br2. It is slightly soluble in water but very soluble in organic solvents. It is a colorless liquid.

Physical properties

At ambient temperature, dibromomethane solidifies around 0.61 GPa. The crystal structure strongly suggests both interhalogen and hydrogen-halogen interactions.

Preparation

Dibromomethane is prepared commercially from dichloromethane via bromochloromethane: :6 CH2Cl2 + 3 Br2 + 2 Al → 6 CH2BrCl + 2 AlCl3 :CH2Cl2 + HBr → CH2BrCl + HCl The latter route requires aluminium trichloride as a catalyst. The bromochloromethane product from either reaction can further react in a similar manner: :6 CH2BrCl + 3 Br2 + 2 Al → 6 CH2Br2 + 2 AlCl3 :CH2BrCl + HBr → CH2Br2 + HCl

In the laboratory, it is prepared from bromoform using sodium arsenite and sodium hydroxide: :CHBr3 + Na3AsO3 + NaOH → CH2Br2 + Na3AsO4 + NaBr

Another way is to prepare it from diiodomethane and bromine.

Uses

Dibromomethane is used as a solvent, gauge fluid, and in organic synthesis (often as 1H-NMR internal standard).

Natural occurrence

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.

References

References

  1. (25 March 2005). "methylene bromide - Compound Summary". National Center for Biotechnology Information.
  2. Dagani, M. J.. "Bromine Compounds".
  3. W. W. Hartman, E. E. Dreger. (1929). "Methylene bromide". Org. Synth..
  4. It conviently converts [[polyol]]s (such as [[catechols]]) to their [[methylenedioxy]] derivatives, and bromomethylenates [[enolate]]s. It is a much cheaper precursor to a [[Simmons-Smith]]-type reagent than [[diiodomethane]].{{cite encyclopedia. Donald S.. Matteson
  5. (December 2006). "Molecular interactions in crystalline dibromomethane and diiodomethane, and the stabilities of their high-pressure and low-temperature phases". Acta Crystallogr. B.
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bromoalkanes halomethanes refrigerants
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