Chemical Properties
Bromomethane is a highly toxic compound and the US EPA has grouped it as a toxicity
class I chemical substance. Bromomethane is a colorless gas or volatile liquid that is usually odorless, but has a sweet, chloroform-like odor at high concentrations and is easily
miscible with ethanol, ether, aromatic carbon disulfi de, and ketones. It decomposes on
heating and, on burning, produces highly toxic and irritating fumes, bromides, carbon
oxybromide, carbon dioxide, and monoxide. It is also used as a general purpose fumigant to kill a variety of pests, including rats and insects, and a gas soil fumigant against insects,
termites, rodents, weeds, nematodes, and soil-borne diseases.
Bromomethane is used for post-harvest fumigation of foods, such as cereals, spices,
dried fruits, nuts, fresh fruits, and vegetables. Although bromomethane is on the list of
banned ozone-depleting chemical substances of the Montreal Protocol, in 2005 and 2006 it
was granted a critical use exemption (under the Montreal Protocol). Bromomethane is an
RUP and should be purchased and used only by certifi ed applicators.
Chemical Properties
Methyl bromide (Bromomethane) is an odorless, sweetish, colorless gas that has been used as a soil fumigant and structural fumigant to control pests across a wide range of agricultural sectors. Methyl bromide is soluble in ethanol, benzene, carbon disulfi de, and sparingly in water. During the 1920s, methyl bromide was used as an industrial fi re extinguishing agent. The current uses of methyl bromide include the fumigation of homes and other structures for the control of termites and other pests. Because methyl bromide depletes the stratospheric ozone layer, the amount produced and imported in the United States was reduced incrementally until it was phased out on January 1, 2005, pursuant to our obligations under the Montreal Protocol on Substances that Deplete the Ozone Layer (Protocol) and the Clean Air Act (CAA).
General Description
Colorless highly toxic volatile liquid or a gas. Boiling point 3.56°C (38.41°F). Usually odorless, but has a sweetish chloroform-like odor at high concentrations. Used as an insecticide, a rodenticide, a fumigant, a nematocide, a chemical intermediate and as a fire extinguishing agent.
Reactivity Profile
METHYL BROMIDE(74-83-9) is incompatible with metals, dimethyl sulfoxide, ethylene oxide. [Lewis]. Can give flammable products if mixed with potassium hydroxide, sodium hydroxide and other strong bases. METHYL BROMIDE(74-83-9) in a steel tank reacted with an aluminum tube (part of the level gauge) producing methyl aluminum bromide. When the latter was subsequently exposed to air, enough heat was produced to ignite the METHYL BROMIDE(74-83-9)-compressed air mixture above the liquid layer. The ensuing explosion shattered the tank (also incompatible with zinc, magnesium, and alloys)[Chem. Eng. Pro. 58(8). 1962]. A reaction between METHYL BROMIDE(74-83-9) and dimethyl sulfoxide resulted in an explosion that shattered the apparatus [NFPA 491M. 1991].
Air & Water Reactions
Nonflammable over a wide range of concentrations in air. Slightly soluble in water (about 1.75 g/100 mL of solution at 20° C). Reacts slowly with water to give methyl alcohol and hydrobromic acid. [K-O Vol. 4].
Hazard
Toxic by ingestion, inhalation, and skin
absorption; strong irritant to skin and upper respiratory tract. Questionable carcinogen.
Health Hazard
Exposures to bromomethane in high concentrations cause headaches, burns the skin, itching, redness, blisters, dizziness, nausea, vomiting, and weakness. Prolonged periods of
exposure cause mental excitement, muscle tremors, seizures, bronchitis and pneumonia,
numbness, tremor, speech defects, damage to the nervous system, lung, nasal mucosa,
kidney, convulsions, respiratory paralysis, coma, and death. Human exposure to bromomethane is predominantly occupational, during manufacture and occupational fi eld
fumigation.
Health Hazard
Exposures to methyl bromide by inhalation cause injury to the brain, nerves, lungs, and throat. At high doses, breathing methyl bromide causes injury to the kidneys and liver. The symptoms of methyl bromide toxicity and poisoning include, but are not limited to, dizziness, headache, abdominal pain, vomiting, weakness, hallucinations, loss of speech, incoordination, labored breathing, and convulsions. Contact with the skin and eyes can lead to irritation and burns. After serious exposures to methyl bromide, occupational workers suffer with lung and/or nervous system-related problems and permanent brain/ nerve damage. Laboratory study with species of animals indicated that bromomethane does not cause birth defects and does not interfere with normal reproduction except at high exposure levels
Health Hazard
Methyl bromide is a dangerous cumulative poison with delayed symptoms of central nervous system intoxication that may appear as long as several months after exposure. High concentrations can produce fatal pulmonary edema. Chronic exposure can cause central nervous system depression and kidney injury. It may cause severe and permanent brain damage. Severe neurological signs may appear when there is a sudden exposure to high concentrations following continuous slight exposure. Methyl bromide has practically no odor or irritating effects and therefore no warning, even at hazardous concentrations.
Potential Exposure
Methyl bromide is used in fire extinguishers; as a fumigant in pest control and as a methylation
agent in industry as an insect fumigant for soil, grain, warehouses, mills, ships, etc. It is also used as a chemical intermediate and a methylating agent; a refrigerant; a herbicide;
a low-boiling solvent in aniline dye manufacture; for
degreasing wool; for extracting oils from nuts, seeds, and
flowers; and in ionization chambers. It is used as an intermediate in the manufacture of many drugs.
Fire Hazard
When heated to decomposition, METHYL BROMIDE emits toxic fumes of bromides. Hazardous polymerization may not occur.
First aid
If this chemical gets into the eyes, remove any
contact lenses at once and irrigate immediately for at least
15 minutes, occasionally lifting upper and lower lids. Seek
medical attention immediately. If this chemical contacts the skin, remove contaminated clothing and wash immediately
with soap and water. Seek medical attention immediately.
If this chemical has been inhaled, remove from exposure,
begin rescue breathing (using universal precautions, including resuscitation mask) if breathing has stopped and CPR if
heart action has stopped. Transfer promptly to a medical
facility. When this chemical has been swallowed, get medical attention. Give large quantities of water and induce
vomiting. Do not make an unconscious person vomit.
Medical observation is recommended for 24 to 48 hours
after breathing overexposure, as pulmonary edema may be
delayed. As first aid for pulmonary edema, a doctor or
authorized paramedic may consider administering a drug or
other inhalation therapy. If frostbite has occurred, seek
medical attention immediately; do NOT rub the affected
areas or flush them with water. In order to prevent further
tissue damage, do NOT attempt to remove frozen clothing
from frostbitten areas. If frostbite has NOT occurred, immediately and thoroughly wash contaminated skin with soap
and water
Shipping
UN1062 Methyl bromide, Hazard Class: 2.3;
Labels: 2.3-Poisonous gas, Inhalation Hazard Zone C.
Cylinders must be transported in a secure upright position,
in a well-ventilated truck. Protect cylinder and labels from
physical damage. The owner of the compressed gas cylinder is the only entity allowed by federal law (49CFR) to
transport and refill them. It is a violation of transportation
regulations to refill compressed gas cylinders without the
express written permission of the owner
Incompatibilities
Attacks aluminum to form spontaneously
flammable aluminum trimethyl. Incompatible with strong
oxidizers, aluminum, dimethylsulfoxide, ethylene oxide;
water. Attacks zinc, magnesium, alkali metals and their
alloys. Attacks some rubbers and coatings. Methyl bromide
reacts with water to generate hydrobromic acid and methanol but the reaction is so slow that it can be disregarded for
most practical purposes.
Waste Disposal
Consult with environmental
regulatory agencies for guidance on acceptable disposal
practices. Generators of waste containing this contaminant
(≥100 kg/mo) must conform to EPA regulations governing
storage, transportation, treatment, and waste disposal. A
poisonous gas. Must be handled by experts: the recommended disposal procedure is to spray the gas into the fire
box of an incinerator equipped with an afterburner and
scrubber (alkali).
Physical properties
Colorless liquid or gas with an odor similar to chloroform at high concentrations. Ruth (1986)
reported odor threshold concentrations ranging from 80 to 4,000 mg/m3.
Occurrence
An organic compound, present in the atmosphere as the result of both natural (oceanic production) and anthropogenic (use as a soil fumigant) sources; this compound is the largest single source of bromine to the stratosphere, with a tropospheric mixing ratio of about 10 parts per trillion (by volume).
Definition
ChEBI: A one-carbon compound in which the carbon is attached by single bonds to three bromine atoms and one hydrogen atom. It is produced naturally by marine algae.
Production Methods
The commercial manufacture of methyl bromide is based on the reaction of hydrogen bromide with methanol. The hydrogen bromide used could be generated in situ from bromine and a reducing agent. The uses of sulfur or hydrogen sulfide as reducing agents are described, the latter process having the advantage. A new continuous process for the production of methyl bromide from methanol and aqueous HBr in the presence of a silica supported heteropolyacid catalyst has recently been described. Methyl bromide can also be coproduced with other organic bromine compounds by the reaction of the methanol solvent with hydrogen bromide formed as a by-product. The processes include coproduction of methyl bromide with bromostyrenes, tribromophenol, potassium and sodium bromide, and especially tetrabromo bisphenol A.
Reactions
Methyl bromide is present in the atmosphere as the result of both natural (oceanic production) and anthropogenic (use as a soil fumigant) sources; this compound is the largest single source of bromine to the stratosphere, with a tropospheric mixing ratio of about 10 parts per trillion (by volume). Methyl bromide reacts with several nucleophiles and is a useful methylation agent for the preparation of ethers, sulfides, amines, etc. Tertiary amines are methylated by methyl bromide to form quaternary ammonium bromides. The reactivity of methyl bromide is summarized in Figure 1.图
Synthesis Reference(s)
Journal of the American Chemical Society, 75, p. 1148, 1953. Applications of the Hunsdiecker Silver Salt Degradation. The Preparation of Dibromides and Tribromides.
DOI: 10.1021/ja01101a041
Agricultural Uses
Fumigant, Herbicide, Insecticide, Nematicide: The primary use of methyl bromide is as an insect
fumigant to control insects, nematodes, weeds and pathogens
in more than 100 crops and for soil, grain storage,
warehouses, mills, ships, etc. Use of methyl bromide in
the U.S. will be phased out under the requirements of the
Montreal Protocol, with some exemptions. Methyl bromide
is also used as a chemical intermediate and a methylating
agent, a refrigerant, a herbicide, a fire-extinguishing
agent, a low-boiling solvent in aniline dye manufacture,
for degreasing wool, for extracting oils from nuts, seeds,
and flowers, and in ionization chambers. It is used as an
intermediate in the manufacture of many drugs. A U.S.
EPA restricted Use Pesticide (RUP), NO INERT. Still
actively
registered for use in the U.S. (2013). As of March
18, 2005, the use of methyl bromide in the EU was banned
for most purposes, including quarantine and pre-shipment
fumigations.Registered for use in the U.S.
Trade name
BROM-O-GAS®; BROM-OSOL
®; DAWSON® 100; DOWFUME®; EDCO®;
EMBAFUME®; HALON 1001®; ISCOBROME®;
KAYAFUME®; MATABROM®; METHO-GAS®; M-B-C
FUMIGANT®; R 40B1®; ROTOX®; TERABOL®;
TERR-O-GAS®; ZYTOX®
Materials Uses
Dry methyl bromide is inert and noncorrosive in
the presence of most structural metals. However,
in the presence of impurities such as alcohols
and water, reactions will take place on zinc,
tin, and iron surfaces. Aluminum and its
alloys should not be used for methyl bromide
service because of the formation of trimethyl
aluminum, which is pyrophoric.
Physiological effects
Methyl bromide is toxic. The vapor is odorless
at low concentrations and nonirritating to the
skin or eyes during exposure; therefore, detection
of overexposure is not possible until the
onset of symptoms. Early symptoms of overexposure
are dizziness, headache, nausea and
vomiting, weakness, and collapse. Lung edema
may develop 2 to 48 hours after exposure, accompanied
by cardiac irregularities. These effects
may cause death. Repeated overexposures
can result in blurred vision, staggering gait, and
mental imbalance, with probable recovery after
a period of no exposure. Blood bromide levels
suggest the occurrence, but not the degree, of
exposure. Treatment is symptomatic.
ACGIH recommends the Threshold Limit
Value-Time-Weighted Average (TLV- TWA)
of I ppm (3.9 mg/m3
) for methyl bromide. The
TLV- TWA is the time-weighted average concentration
for a normal 8-hour workday and a
40-hour workweek, to which nearly all workers
may be repeatedly exposed, day after day, without
adverse effect.
Carcinogenicity
Data on the carcinogenicity of
bromomethane for oral exposure are lacking, but oral exposure
is unlikely due to the volatility of bromomethane.
A 1-year study in dogs consuming bromomethane-exposed
food found no evidence of carcinogenicity. Data on
carcinogenicity in humans following inhalation exposure in
humans are not available. Animal inhalation studies exist
but do not demonstrate evidence of bromomethane-induced
carcinogenic changes. They include studies in F344
and Wistar rats, and in B6C3F1 and Crj:BDF1. The EPA
descriptor for cancer is “inadequate information to assess
the carcinogenic potential of bromomethane in humans.”
Specifically, IRIS states: “Inadequate human and animal data: a single mortality study from which direct exposure
associations could not be deduced and studies in several
animal species with too few animals, too brief exposure or
observation time for adequate power.” Bromomethane has
shown genotoxicity. NAS reported that although methyl
bromide is genotoxic without metabolic activation and has
been shown to alkylate DNA in different organs in in vivo
studies, there is no clear evidence of oncogenicity under
experimental conditions used in the chronic inhalation studies
with rat and mice.
Source
Drinking water standard: No MCLGs or MCLs have been proposed, however, a DWEL of 50
μg/L was recommended (U.S. EPA, 2000).
Environmental Fate
Photolytic. When methyl bromide and bromine gas (concentration = 3%) was irradiated
at 1850 ?, methane was produced (Kobrinsky and Martin, 1968).
Chemical/Physical. Methyl bromide hydrolyzes in water forming methanol and hydrobromic
acid. The estimated hydrolysis half-life in water at 25°C and pH 7 is 20 days
(Mabey and Mill, 1978). Forms a voluminous crystalline hydrate at 0–5°C (Keith and
Walters, 1992).
When methyl bromide was heated to 550°C in the absence of oxygen, methane,
hydrogen, bromine, ethyl bromide, anthracene, pyrene and free radicals were produced
(Chaigneau et al., 1966).
Emits toxic bromide fumes when heated to decomposition (Lewis, 1990).
Metabolic pathway
Methyl bromide degrades in aqueous and soil environments mainly via
dehalogenation to yield bromide ions with the incorporation of the
methyl carbon moiety into polar natural components.
Purification Methods
Purify it by bubbling through conc H2SO4, followed by passage through a tube containing glass beads coated with P2O5. Also purify it by distillation from AlBr3 at -80o, by passage through a tower of KOH pellets and by partial condensation. [Beilstein 1 IV 68.]
Degradation
Methyl bromide is hydrolysed at neutral pH to methanol and bromide
ion. The DT50s of methyl bromide in water at 17 and 25 °C were 21 and
75 days, respectively (Jeffers and Wolfe, 1996a; Mabey and Mill, 1978;
Moelwyn-Hughes, 1938). Aqueous photolysis is not a major environmental
degradation process.
In the upper and mid stratosphere (>20 km), photodegradation of
MeBr with hydroxy radicals is reported to yield various products such as
Br, BrO and HBr (Honaganahalli and Seiber, 1996).
Toxicity evaluation
Methyl bromide is a methylating agent and can bind irreversibly
to sulfhydryl groups of enzymes and proteins. Methyl bromideinduced
neurotoxicity has been attributed to its inhibition of
the detoxification enzyme glutathione-S-transferase (GST), and
depletion of glutathione in the brain. The degeneration of rat
olfactory epithelium may also be related to the inhibition of
GST as well as the generally high metabolic activity at this site.
Glutathione involvement in the toxicity is demonstrated by the
higher survival in rats given exogenous glutathione when
exposed to a lethal dose of methyl bromide. Methyl bromide
genotoxicity may be associated withDNAalkylation. The role of
bromide is unclear because its level has not correlated with the
symptoms of poisoning in humans.
GRADES AVAILABLE
Methyl bromide is sold either as a pure compound,
99.8 percent minimum, or with an odorant,
chloropicrin (typically 2 percent).
