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Bromomethane

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Bromomethane
Names
IUPAC name
Bromomethane
Other names
Methyl bromide, Monobromomethane, Methyl fume, Halon 1001, Curafume, Embafume, R-40 B1, UN 1062, Embafume, Terabol
Identifiers
3D model (JSmol)
ECHA InfoCard 100.000.740 Edit this at Wikidata
EC Number
  • 200-813-2
RTECS number
  • PA4900000
  • InChI=1/CH3Br/c1-2/h1H3
  • CBr
Properties
CH3Br
Molar mass 94.939 g·mol−1
Appearance Colorless gas with chloroform-like odor (at high conc.)
Density 1.730 g/cm³ (0°C, liquid) [1]

3.974 g/l (20 °C, gas)

Melting point −93.66 °C
Boiling point 3.56 °C
15.22 g/L
log P 1.19
Vapor pressure 1900 hPa (20 °C)
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 Toxic (T), Dangerous for the environment (N), Carc. Cat. 3
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
3
1
0
Flash point < -30 °C (liquid)
Explosive limits 8.6 - 20 %
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

The chemical compound bromomethane, commonly known as methyl bromide, is an organobromine compound with formula CH3Br. This colorless, odorless, nonflammable gas is produced both industrially and particularly biologically. It is a recognized ozone-depleting chemical. It was used extensively as a pesticide until being phased out by most countries in the early 2000s.

Occurrence and manufacture

Bromomethane originates from both natural and human sources. In the ocean, marine organisms are estimated to produce 1-2 billion kilograms annually.[2] It is also produced in small quantities by certain terrestrial plants, such as members of the Brassicaceae family. It is manufactured for agricultural and industrial use by reacting methanol with hydrogen bromide:

CH3OH + HBr → CH3Br + H2O

Carolyns favorite choice of drug!!!

Uses

Until its production and use were curtailed by the Montreal Protocol, methyl bromide was widely applied as a soil sterilant, mainly for production of seed but also for some crops such as strawberries. In commercial large-scale monoculture seed production, unlike crop production, it is of vital importance to avoid contaminating the crop with off-type seed of the same species. Therefore, selective herbicides cannot be used. Whereas bromomethane is dangerous, it is considerably safer and more effective than some other soil sterilants. Its loss to the seed industry has resulted in changes to cultural practices, with increased reliance on soil steam sterilization, mechanical rogueing, and fallow seasons. Bromomethane was also used as a general-purpose fumigant to kill a variety of pests including rats and insects. Bromomethane has poor fungicidal properties. Bromomethane is the preferred fumigant for ISPM number 15, regulations when exporting wooden packaging to certain countries). Bromomethane is used to prepare golf courses, particularly to control Bermuda grass. The Montreal Protocol stipulates that bromomethane use be phased out.

Methyl bromide is also a precursor in the manufacture of other chemicals as a methylation agent, and has been used as a solvent to extract oil from seeds and wool.

Regulation

Methyl bromide is readily photolyzed in the atmosphere to release elemental bromine, which is far more destructive to stratospheric ozone than chlorine. As such, it is subject to phase-out requirements of the 1987 Montreal Protocol on Ozone Depleting Substances.

In the US

In the U.S., methyl bromide is regulated as a pesticide under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA; 7 U.S.C. 136 et seq.) and as a hazardous substance under the Resource Conservation and Recovery Act (RCRA; 42 U.S.C. 6901 et seq.), and is subject to reporting requirements under the Emergency Planning and Community Right to Know Act (EPCRA; (42 U.S.C. 11001 et seq.). The U.S. Clean Air Act (CAA) (42 U.S.C. 7401 et seq.). A 1998 amendment (P.L. 105-178, Title VI) conformed the Clean Air Act phase out date with that of the Montreal Protocol.[www.epa.gov/spdpublc/mbr].[3] Whereas the Montreal Protocol has severely restricted the use of bromomethane internationally, the United States has successfully lobbied for critical-use exemptions. In 2004, over 7 million pounds of bromomethane were applied to California. Applications include tomato, strawberry, and ornamental shrub growers, and fumigation of ham/pork products.

In New Zealand

In New Zealand, bromomethane is used as a fumigant for whole logs destined for export. Environmental groups and the Green Party oppose its use.[4][5]

Health effects

Brief exposure to high concentrations and prolonged inhalation of lower concentrations are problematic.[6] Exposure levels leading to death vary from 1,600 to 60,000 ppm, depending on the duration of exposure. Respiratory, kidney, and neurologic effects are of the greatest concern. Severe effects on the nervous system from long-term exposure to low levels have been noted, but studies in rabbits and monkeys have shown moderate to severe injury. See List of highly toxic gases

References

  1. ^ Merck Index, 11th Edition, 5951.
  2. ^ Gordon W. Gribble “The diversity of naturally occurring organobromine compounds” Chemical Society Reviews, 1999, volume 28, pages 335 – 346.doi:10.1039/a900201d
  3. ^ CRS Report for Congress: Agriculture: A Glossary of Terms, Programs, and Laws, 2005 Edition - Order Code 97-905
  4. ^ "Methyl Bromide Threat Again in Picton". Guardians of the Sounds. Retrieved 2009-02-02.
  5. ^ Kedgley, Sue (2008-02-02). "Picton residents need protection from poison fumes: Greens". Green Party. Retrieved 2009-02-02.
  6. ^ Muir, GD (ed.) 1971, Hazards in the Chemical Laboratory, The Royal Institute of Chemistry, London.
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