methyl bromide

Bromomethane
IUPAC name	Bromomethane
Other names	Methyl bromide, Monobromomethane, Methyl fume, Halon 1001, Curafume, Embafume, R-40 B1, UN 1062, Embafume, Terabol
Identifiers
CAS number	74-83-9 Y
PubChem	6323
EC number	200-813-2
RTECS number	PA4900000
SMILES	BrC
InChI	1/CH3Br/c1-2/h1H3
InChI key	GZUXJHMPEANEGY-UHFFFAOYAV
ChemSpider ID	6083
Properties
Molecular formula	CH3Br
Molar mass	94.94 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
Solubility in water	15.22 g/L
log P	1.19
Vapor pressure	1900 hPa (20 °C)
Hazards
R-phrases	R23/24/25, R34, R36/37/38, R45, R48/20, R50, R59, R68
S-phrases	(S1/2), S15, S27, S36/39, S38, S45, S59, S61
NFPA 704	1 3 0
Flash point	< -30 °C (liquid)
Autoignition temperature	535 °C
Explosive limits	8.6 - 20 %
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

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

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.

Methyl Bromide was once used in specialty fire extinguishers, prior to the advent of less toxic halons, as it is electrically non-conductive and leaves no residue. It was used primarily for electrical substations, military aircraft, and other industrial hazards. It was never as popular as other agents due to its high cost and toxicity. MB was used from the 1920s to the 60s, and continued to be used in aircraft engine fire suppression systems into the late 60s.

A selection of stored-pressure methyl bromide fire extinguishers, circa 1930s-40s, UK

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.

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.^[3][4]

United States

In the United States 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.^[5][6] 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.

Chile

Has to phase out the use in agriculture by 2015.^{[citation needed]}

Health effects

Brief exposure to high concentrations and prolonged inhalation of lower concentrations are problematic.^[7] 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

External links

• Methyl Bromide Technical Fact Sheet - National Pesticide Information Center
• Methyl Bromide General Fact Sheet - National Pesticide Information Center
• Methyl Bromide Pesticide Information Profile - Extension Toxicology Network
• International Chemical Safety Card 0109
• NIOSH Pocket Guide to Chemical Hazards 0400
• Institut national de recherche et de sécurité (1992). "Bromométhane."PDF Fiche toxicologique n° 67. Paris:INRS. (French)
• European Chemicals Bureau
• IARC Summaries & Evaluations Vol. 71 (1999)
• The banned pesticide in our soil
• MSDS at Oxford University
• Toxicological profile
• Environmental Health Criteria 166
• OECD SIDS document
• EPA 2010 Critical Use Exemption Nominations
• ChemSub Online (Bromomethane).