description
Methyl bromide (CH3Br) is a halogenated aliphatic hydrocarbon. It is a colorless gas at room temperature and standard pressure.It is 3 times heavier than air. It is odorless except at high concentrations, when it has a burning taste and sweet, chloroformlike smell. Commercially, it is available as a liquefied gas. Some formulations also contain chloropicrin or amyl acetate as a warning agent.
Methyl bromide has been used to treat dry packaged foods in mills and warehouses as well as used as a soil fumigant to control nematodes and fungi.
uses
Methyl bromide was used as an anesthetic in the early 1900s, but fatalities halted this practice. Today, methyl bromide is used widely as a fumigant for all types of dry food stuffs, in grain elevators, mills, ships, warehouses, green-houses, and food-processing facilities for the control of nematodes, fungi, and weeds. It is also used as an insecticide, fire extinguisher, and refrigerant, although its domestic use was banned in 1987. Methyl bromide is also used as a methylating chemical in manufacturing and as a low-boiling solvent for extracting oils from nuts, seeds, and flowers. It is termed a structural or commodity fumigant, which is a class term from the Environmental Protection Agency.
Historically, poisonings involving the general public were mainly associated with the methyl bromide used in fire extinguishers. Other poisoning involved unauthorized entry into buildings being fumigated with methyl bromide.
Methyl bromide has a threshold limit value–time weighted average (TLV-TWA) of 5 ppm and the IDLH concentration is 2,000 ppm. The Occupational Safety and Health Administration (OSHA) permissible exposure limit is 20 ppm.
Health Hazard
Methyl bromide is very irritating to the lower respiratory tract. It is thought that the parent compound is responsible for the toxicity of the methyl bromide, with the mechanism of toxicity possibly having to do with its ability to methylate sulfhydryl enzymes. Exposure to high concentrations of methyl bromide can lead to pulmonary edema or hemorrhage, and typically of delayed onset (several hours after exposure). Symptoms of acute intoxication include those consistent with central nervous system depression such as headache, dizziness, throat irritation, nausea, cough visual disturbances, vomiting, and ataxia. Exposures to very high concentrations can lead to unconsciousness. In cases of exposure to fatal levels of methyl bromide, death typically occurs within 4–6h to 1–2 days postexposure, with the cause of death being respiratory or cardiovascular failure resulting from pulmonary edema. Dermal exposure to liquid methyl bromide can cause skin damage in the form of burning, itching, and blistering. Treatment of methyl bromide poisoning is symptomatic and also includes removal of contaminated clothing. The USEPA Office of Pesticide Programs has classified methyl bromide as Not Likely to be Carcinogenic in Humans.
https://www.unep.org/
Toxicodynamics
The mode of action of methyl bromide is still not understood. Several mechanisms of toxicity are postulated, including the direct cytotoxic effect of the intact methyl bromide molecule or toxicity due to one of its metabolites.
Methyl bromide is a potent alkylating agent with high affinity for sulfhydryl and amino groups. It reacts in vitro with a number of sulfhydrylcontaining enzymes and causes irreversible inhibition of microsomal metabolism. It binds to amine groups in amino acids, interfering with protein synthesis and function. Also it may methylate many other cellular components such as GSH, proteins, DNA, and RNA.The methanethiol and formaldehyde metabolites may have a role in neurologic and visual changes. The bromide ion concentrations are insufficient to explain methyl bromide toxicity.
Description
Methyl bromide is a colorless liquid or gas with
practically no odor. It is a poisonous gas at
room temperature and atmospheric pressure. At
high concentrations, it has a chloroform-like
odor. Detection of lower concentrations is often
facilitated by a warning odorant, chloropicrin,
which is added by the manufacturer.
Methyl bromide is flammable only in the
range of 10 percent to 16 percent by volume in
air. Its physical properties do not meet the definition
of a flammable gas as defined by DOT
and TC. The onset of thermal decomposition
occurs at approximately 752°F (400°C).
Chemical Properties
Methyl bromide is a colorless gas with a
chloroform-like odor at high concentrations. A liquid below 3.3C. Shipped as a liquefied compressed gas.
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/m
3.
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).
Uses
Methyl bromide is used as a fumigant forpest control, for degreasing wool, and as a methylating agent. Its use as a refrigerant andin fire extinguishers is restrained because ofits health hazards.
Uses
The primary pre-harvest uses of methyl bromide are as fumigant
to control a broad spectrum of insects, nematodes, bacteria, fungi and
weeds in grapes, vegetables and strawberries cultivation. Major postharvest
use is in the quarantine control of agricultural commodities such
as the disinfestation of potatoes and tomatoes.
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.
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
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.
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].
Reactivity Profile
Methyl bromide 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 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 -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 and dimethyl sulfoxide resulted in an explosion that shattered the apparatus [NFPA 491M. 1991].
Hazard
Toxic by ingestion, inhalation, and skin
absorption; strong irritant to skin and upper respiratory tract. Questionable carcinogen.
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.
Fire Hazard
When heated to decomposition, Methyl bromide emits toxic fumes of bromides. Hazardous polymerization may not occur.
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®
Mechanism of action
Respiratory action, highly toxic. The mode of action of bromomethane as a pesticide is not fully understood, but it is believed to involve the methylation of certain macromolecules such as DNA, lipids, and certain enzymes, as well as disruption of neurotransmitter processes. This process is thought to disrupt the normal functioning of these molecules, leading to various toxic effects.
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.
Safety Profile
Suspected carcinogen
with experimental carcinogenic data. A
human poison by inhalation. Human
systemic effects by inhalation: anorexia,
nausea or vomiting. Corrosive to skin; can
produce severe burns. Human mutation data
reported. A powerful fumigant gas that is
one of the most toxic of the common
organic hahdes. It is hemotoxic and narcotic
with delayed action. The effects are
cumulative and damaging to nervous system,
hdneys, and lung. Central nervous system
effects include blurred vision, mental
confusion, numbness, tremors, and speech
defects.
Methyl bromide is reported to be eight
times more toxic on inhalation than ethyl
bromide. Moreover, because of its greater
volatility, it is a much more frequent cause
of poisoning. Death following acute
poisoning is usually caused by its irritant
effect on the lungs. In chronic poisoning,
death is due to injury to the central nervous
system. Fatal poisoning has always resulted
from exposure to relatively high
concentrations of methyl bromide vapors
(from 8600 to 60,000 ppm). Nonfatal
poisoning has resulted from exposure to
concentrations as low as 100-500 ppm. In
addtion to injury to the lung and central
nervous system, the kidneys may be
damaged, with development of albuminuria
and, in fatal cases, cloudy swelhng and/or tubular degeneration. The liver may be
enlarged. There are no characteristic blood
changes.
Mixtures of 10-1 5 percent with air may be
ignited with difficulty. Moderately explosive
when exposed to sparks or flame. Forms
explosive mixtures with air within narrow
limits at atmospheric pressure, with wider
limits at higher pressure. The explosive
sensitivity of mixtures with air may be
increased by the presence of aluminum,
magnesium, zinc, or their alloys.
Incompatible with metals, dunethyl
sulfoxide, ethylene oxide. To fight fire, use
foam, water, CO2, dry chemical. When
heated to decomposition it emits toxic
fumes of Br-. See also BROMIDES
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.
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.
First aid
If this chemical gets into the eyes, remove any contact lenses at once and irrigate immediately for at least 15 min, 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 2448 h after breathing overexposure, as pulmonary edema may be delayed. As first aid for pulmonary edema, a doctor or authorized paramedic may consider administering a corticosteroid spray. 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.
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.
storage
Methyl bromide (Bromomethane) should be kept stored in sealed containers to keep it from evaporating.
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
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.]
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.
Degradation
Methyl bromide is hydrolysed at neutral pH to methanol and bromide
ion. The DT
50s 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).
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.
Toxics Screening Level
The current lTSL for Methyl Bromide (bromomethane) (5 μg/m3 ) was derived on May 11, 1993.
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).
Precautions
Occupational workers should use appropriate ventilation during production and formulation of bromomethane at the workplace. The ventilation must be suffi cient to maintain the
levels of bromomethane below the prescribed OEL. Local exhaust ventilation at source or
vapor extraction may also be used. Gloves or rubber boots should not be used as the liquid
or concentrated vapor may be trapped inside them
GRADES AVAILABLE
Methyl bromide is sold either as a pure compound,
99.8 percent minimum, or with an odorant,
chloropicrin (typically 2 percent).
Pesticide Type
Soil sterilant; Insecticide
