Methyl bromide

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/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).

The Uses of Methyl bromide

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.

The Uses of Methyl bromide

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®

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.]

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.

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).

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).