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*[http://www.inchem.org/documents/sids/sids/methbrom.pdf OECD SIDS document]
*[http://www.inchem.org/documents/sids/sids/methbrom.pdf OECD SIDS document]
*[http://www.epa.gov/ozone/mbr/2010_nomination.html EPA 2010 Critical Use Exemption Nominations]
*[http://www.epa.gov/ozone/mbr/2010_nomination.html EPA 2010 Critical Use Exemption Nominations]
*[http://chemsub.online.fr/chemsearch/cas_number_74-83-9.html ChemSub Online (Bromomethane)].


{{Halomethanes}}
{{Halomethanes}}

Revision as of 21:24, 25 April 2009

Bromomethane
Names
IUPAC name
Bromomethane
Other names
Methyl bromide, Monobromomethane, Methyl fume, Halon 1001, Curafume, Embafume, R-40 B1, UN 1062
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 organic halogen compound with formula CH3Br. It is a colorless, nonflammable gas with no distinctive smell. Its chemical properties are quite similar to those of chloromethane. 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. Trade names for bromomethane include Embafume and Terabol.

Occurrence and manufacture

Bromomethane originates from both natural and human sources. It occurs naturally in the ocean, where it is found in some species of kelp.[citation needed] It is also produced in small quantities by certain terrestrial plants, such as members of the Brassicaceae family.[citation needed] It is manufactured for agricultural and industrial use by reacting methanol with hydrobromic acid.

Uses

Until its production and use was curtailed by the Montreal Protocol, it was widely used 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. While bromomethane is dangerous to use, it is considerably safer and more effective than the few other soil sterilants available. 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). It 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.

While the Montreal Protocol has severely restricted the use of bromomethane internationally, the United States has successfully pushed for critical-use exemptions of the chemical. In 2004, the most recent year with available data, over 7 million pounds of bromomethane were applied to California fields, according to pesticide use statistics compiled by the California Department of Pesticide Regulation.

Ozone depletion

Bromomethane is on the list of banned ozone-depleting substances of the Montreal Protocol. Because bromine is 60 times[1] more destructive to ozone than chlorine, even small amounts of bromomethane cause considerable damage to the ozone layer. In 2005 and 2006, however, it was granted a critical use exemption under the Montreal Protocol.

Controversy

Bromomethane is used to prepare golf courses and sod for golf courses and elsewhere, particularly to control Bermuda grass. The Montreal Protocol stipulates that bromomethane use be phased out. The most recent set of 'critical use' exemptions in the US include use of Bromomethane for tomato, strawberry, and ornamental shrub growers, and fumigation of ham/pork products.

In New Zealand bromomethane is used as a fumigant for whole logs destined for export. Environmental groups and the Green Party oppose its use because it its toxicity, effect on the ozone layer and the difficulty in controlling gas emissions.[2][3]

Health effects

If inhaled in high concentration for a short period, it produces headaches, dizziness, nausea, vomiting and weakness; this may be followed by mental excitement, convulsions and even acute mania. More prolonged inhalation of lower concentrations may cause bronchitis and pneumonia.[4]

With a low boiling point of 4 °C, the liquid causes frostbite on contact with skin.[5], then blisters several hours after contact. Both liquid and vapour severely damage the eyes.[4]

Exposure levels leading to death vary from 1,600 to 60,000 ppm, depending on the duration of exposure.

The respiratory, kidney, and neurologic effects are of the greatest concern to people. No cases of severe effects on the nervous system from long-term exposure to low levels have been noted in people, but studies in rabbits and monkeys have shown moderate to severe injury.

Sources and sinks

Sources of CH3Br include oceanic production, biomass burning, leaded fuel combustion, and fumigation of soils, durable goods, perishables, and structures.[citation needed] Sinks include photochemical decomposition in the atmosphere (reaction with hydroxyl radicals (OH) and photolysis at higher altitudes), loss to soils, chemical and biological degradation in the ocean, and uptake by green plants.

References

  1. ^ Merck Index, 11th Edition, 5951.
  2. ^ "Methyl Bromide Threat Again in Picton". Guardians of the Sounds. Retrieved 2009-02-02.
  3. ^ Kedgley, Sue (2008-02-02). "Picton residents need protection from poison fumes: Greens". Green Party. Retrieved 2009-02-02.
  4. ^ a b Muir, GD (ed.) 1971, Hazards in the Chemical Laboratory, The Royal Institute of Chemistry, London.
  5. ^ "Methyl Bromide". INCHEM ICSC.
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