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Dibromomethane

Names
Preferred IUPAC name Dibromomethane
Other names Methyl dibromide Methylene bromide Methylene dibromide Refrigerant-30B2
Identifiers
CAS Number	74-95-3
3D model (JSmol)	Interactive image
Abbreviations	DBM MDB UN 2664
Beilstein Reference	969143
ChEBI	CHEBI:47077
ChemSpider	2916
ECHA InfoCard	100.000.750
EC Number	200-824-2
Gmelin Reference	25649
MeSH	methylene+bromide
PubChem CID	3024
RTECS number	PA7350000
UNII	V69B659W01
UN number	2664
CompTox Dashboard (EPA)	DTXSID4021557
InChI InChI=1S/CH2Br2/c2-1-3/h1H2Key: FJBFPHVGVWTDIP-UHFFFAOYSA-N
SMILES BrCBr
Properties
Chemical formula	CH2Br2
Molar mass	173.835 g·mol
Appearance	Colorless to yellow liquid
Density	2.477 g⋅mL
Melting point	−52.70 °C; −62.86 °F; 220.45 K
Boiling point	96 to 98 °C; 205 to 208 °F; 369 to 371 K
Solubility in water	12.5 g⋅L (at 20 °C)
Vapor pressure	4.65 kPa (at 20.0 °C)
Henry's law constant (kH)	9.3 μmol⋅Pa⋅kg
Magnetic susceptibility (χ)	−65.10·10⋅cm/mol
Refractive index (nD)	1.541
Thermochemistry
Heat capacity (C)	104.1 J⋅K⋅mol
Hazards
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H332, H412
Precautionary statements	P273
NFPA 704 (fire diamond)	2 0 0
Lethal dose or concentration (LD, LC):
LD50 (median dose)	1 g⋅kg (oral, rabbit) 3.738 g⋅kg (subcutaneous, mouse) >4 g⋅kg (dermal, rabbit)
Related compounds
Related alkanes	Bromoform Tetrabromomethane 1,1-Dibromoethane 1,2-Dibromoethane
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). Y verify (what is  ?) Infobox references

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 freezes 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 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.

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

1. "methylene bromide - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 25 March 2005. Identification. Retrieved 18 June 2012.
2. Podsiadlo M.; Dziubek K.; Szafranski M.; Katrusiak A. (December 2006). "Molecular interactions in crystalline dibromomethane and diiodomethane, and the stabilities of their high-pressure and low-temperature phases" (PDF). Acta Crystallogr. B. 62 (6): 1090–1098(9). doi:10.1107/S0108768106034963. PMID 17108664. Retrieved 2007-06-29.
3. ^ Dagani, M. J.; Barda, H. J.; Benya, T. J.; Sanders, D. C. "Bromine Compounds". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a04_405. ISBN 978-3527306732.
4. W. W. Hartman, E. E. Dreger (1929). "Methylene bromide". Org. Synth. 9: 56. doi:10.15227/orgsyn.009.0056.
5. Matteson, Donald S. "Dibromomethane". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rd044.

External links

• International Chemical Safety Card 0354

• Bromoalkanes
• Halomethanes
• Refrigerants