METHYL MERCAPTAN Chemical Properties
- Melting point:
- −123 °C(lit.)
- Boiling point:
- 6 °C(lit.)
- vapor density
- 1.66 (vs air)
- vapor pressure
- 1536 mm Hg ( 20 °C)
- refractive index
- 1.4020 (estimate)
- 2716 | METHYL MERCAPTAN
- Flash point:
- Soluble in alcohol, ether (Weast, 1986), and petroleum naphtha (Hawley, 1981)
- 10.3(at 25℃)
- explosive limit
- Water Solubility
- 23.30 g/L at 20 °C (quoted, Windholz et al., 1983)
0.330 mol/L at 25 °C (Hine and Weimar, 1965)
- JECFA Number
- Henry's Law Constant
- 3.03 (Hine and Weimar, 1965)
- Exposure limits
- TLV-TWA 0.5 ppm (～1.0 mg/m3 ) (ACGIH and MSHA); ceiling 10 ppm (OSHA); IDLH 400 ppm (NIOSH); the revised IDLH is 150 ppm in analogy to H2S.
- Stable. Highly flammable - note low flash point. Reacts vigorously or explosively with a wide variety of materials - consult a full MSDS data sheet before using. Incompatible with strong oxidizing agents, alkali and alkaline earth metals, epoxides, hydrazines, ketones, lead, mercury (II) oxide, azo- and diazo- compounds, copp
- CAS DataBase Reference
- 74-93-1(CAS DataBase Reference)
- Language:English Provider:SigmaAldrich
METHYL MERCAPTAN Usage And Synthesis
Methanethiol (also known as methyl mercaptan) is a colorless gas with a smell like rotten cabbage. It is a natural substance found in the blood and brain of humans and other animals as well as plant tissues. It is disposed of through animal feces. It occurs naturally in certain foods, such as some nuts and cheese. It is also one of the main chemicals responsible for bad breath and the smell of flatus. The chemical formula for methanethiol is CH3SH; it is classified as a thiol. It is sometimes abbreviated as MeSH. It is very flammable.
colourless gas with a garlic-like or rotten cabbage-like smell
Methyl mercaptan is a colorless gas or white liquid with a disagreeable odor like garlic or rotten cabbage. Shipped as a liquefied compressed gas. The odor threshold is 0.002 ppm.
Methyl mercaptan has an objectionable odor of decomposing cabbage. May be prepared by heating an aqueous solution of potassium methyl sulfate and KHS; from sodium methyl sulfate and potassium sulfhydrate; also from methanol and hydrogen sulfide in the presence of a catalyst.
Methyl mercaptan has an objectionable odor of decomposing cabbage or garlic
Colorless gas with a garlic-like or rotten cabbage odor. An experimentally determined odor threshold concentration of 2.1 ppbv was reported by Leonardos et al. (1969). A detection odor threshold concentration of 81 μg/m3 (41 ppbv) was determined by Katz and Talbert (1930).
Methanethiol is released from decaying organic matter in marshes and is present in the natural gas of certain regions, in coal tar, and in some crude oils.
In surface seawater, methanethiol is the primary breakdown product of the algal metabolite dimethylsulfoniopropionate (DMSP). Marine bacteria appear to obtain most of their protein sulfur by the breakdown of DMSP and incorporation of methanethiol, despite the fact that methanethiol is present in seawater at much lower concentrations than sulfate (～0.3 nM vs. 28 mM). Bacteria in oxic and anoxic environments can also convert methanethiol to dimethyl sulfide (DMS), although most DMS in surface seawater is produced by a separate pathway. Both DMS and methanethiol can be used by certain microbes as substrates for methanogenesis in some anaerobic soils.
Methanethiol is a weak acid, with a pKa of ～10.4. This acidic property makes it reactive with dissolved metals in aqueous solutions. The environmental chemistry of these interactions in seawater or fresh water environments such as lakes has yet to be fully investigated.
A material safety data sheet (MSDS) lists methanethiol as a colorless, flammable gas with an extremely strong and repulsive smell. At very high concentrations it is highly toxic and affects the central nervous system. Its penetrating odor provides warning at dangerous concentrations. An odor threshold of 1 ppb has been reported. The United States OSHA Ceiling Limit is listed as 10 ppm.
Methanethiol is mainly used to produce methionine, which is used as a dietary component in poultry and animal feed. Methanethiol is also used in the plastics industry and as a precursor in the manufacture of pesticides. It is released as a by-product of wood pulping in pulp mills.
Methanethiol is also used for communication in mining operations . Releasing the substance into the ventilation system is generally the most efficient and reliable means to alert all workers of an emergency , and is referred to as "releasing the pest" ,This substance's strong odor alerts the miners to immediately go to a saferoom.
Since natural gas and propane are colorless and odorless, a small amount of methyl mercaptan or ethyl mercaptan is added to make it easy to detect a gas leak.
Methanethiol is used in the manufacture ofpesticides and fungicides and as an intermediate in the manufacture of jet fuels (Watkinset al. 1989); it is added to natural gas to giveodor. It is used in the synthesis of methionine.
Synthesis, especially of methionine, jet fuel additives, fungicides; also as catalyst.
Methanethiol is prepared commercially by the reaction of methanol with hydrogen sulfide gas over an acidic solid catalyst, such as alumina. It can be prepared by the reaction of methyl iodide with thiourea.
Aroma threshold values
Detection: 0.02 to 4 ppb. Aroma characteristics at 1.0%: vegetable oil, alliaceous, eggy, creamy with savory nuances
Taste threshold values
Taste characteristics at 1 ppm: sulfurous, alliaceous, creamy with a surface-ripened cheese top note and a clean, savory, meaty depth
Air & Water Reactions
Highly flammable. Reacts with water, steam or acids to produce toxic, flammable vapors [Lewis].
METHYL MERCAPTAN is a reducing agent--can react vigorously with oxidizing agents. Dangerous fire or explosion hazard when exposed to heat, flame, sparks or strong oxidizing agents (e.g., calcium hypochlorite). When heating to decomposition emits highly toxic fumes of oxides of sulfur [Lewis, 3rd ed., 1993, p. 862]. Violent reaction with mercury(II) oxide [Klason P., Ber., 1887, 20, p. 3410].
Flammable, dangerous fire risk. Explosive limits in air 3.9–21.8%. Strong irritant. Liver damage.
Can cause death by respiratory paralysis. It is an eye and respiratory tract irritant. Exposure results in pulmonary edema and hepatic and renal damage.
The acute toxicity of methanethiol is simi-lar to that of hydrogen sulfide. Inhalation ofthis gas can cause narcosis, headache, nau-sea, pulmonary irritation, and convulsions inhumans. Other symptoms noted are acutehemolytic anemia, methemoglobinemia, andcyanosis. In humans, several hours exposure to about 5 ppm concentration of thisgas can cause headache and nausea. Exposure to high concentrations can result inrespiratory paralysis and death. The 2-hour inhalation LC50 value in mice is within therange 650 mg/m3.Shults et al. (1970) reported a case of ahuman death from overexposure to methane-thiol. The victim developed acute hemolyticanemia and methemoglobinemia and re-mainedindeepcomauntil deaththatoccurred28 days after the accident from emptying gascylinders.
Combustion produces irritating sulfur dioxide. Flash back along vapor track may occur. Very dangerous when exposed to heat, flame, or oxidizers. On decomposition METHYL MERCAPTAN emits highly toxic fumes of sulfur oxides. METHYL MERCAPTAN will react with water, steam or acids to produce toxic and flammable vapors; and can react vigorously with oxidizing materials. Irritating sulfur dioxide is produced upon combustion. When heated to decomposition, METHYL MERCAPTAN emits highly toxic fumes and flammable vapors. Incompatible with mercuric oxide and oxidizing materials. Avoid direct sunlight, and areas of high fire hazards. Hazardous polymerization may not occur.
Poison by inhalation. Mutation data reported. A common air contaminant. Very dangerous fire hazard when exposed to heat or flame; can react vigorously with oxidzing materials. Explosive in the form of vapor when exposed to heat or flame. Reacts with water, steam, or acids to produce toxic and flammable vapors. Violent reaction with mercury(II) oxide. To fight fire, use alcohol foam, CO2, dry chemical. Upon decomposition it emits highly toxic fumes of SOx.
By heating an aqueous solution of potassium methyl sulfate and KHS; from sodium methyl sulfate and potassium sulfhydrate; also from methanol and hydrogen sulfide in the presence of a catalyst
Methyl mercaptan is used in methionine synthesis, and widely as an intermediate in pesticide manufacture. A foul-smelling odorant usually added to chemicals, including pesticides.
Occurs naturally in kohlrabi stems (Brassica oleracea var. gongylodes) and potato plants (Duke, 1992)
Biological. After 20 d, methyl mercaptan started to degrade in anaerobic sediments and sludges
producing stoichiometric amounts of methane. Complete degradation was achieved after 20 d. Under
anaerobic freshwater conditions, methyl mercaptan were degraded by methanogenic archea (van
Leerdam et al., 2006).
Photolytic. Sunlight irradiation of a methyl mercaptan-nitrogen oxide mixture in an outdoor chamber yielded formaldehyde, sulfur dioxide, nitric acid, methyl nitrate, methanesulfonic acid, and an inorganic sulfate (Grosjean, 1984a).
Chemical/Physical. In the presence of nitric oxide, gaseous methyl mercaptan reacted with OH radicals forming methyl sulfenic acid and methyl thionitrite. The rate constant for this reaction is 2.1 x 10-11 cm3/molecule?sec at 20 °C (MacLeod et al., 1984). Forms a crystalline hydrate with water (Patnaik, 1992).
UN1064 Methyl mercaptan, Hazard Class: 2.3; Labels: 2.3-Poisonous gas, 2.1-Flammable 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.
Methanethiol is a byproduct produced by the metabolism of asparagus. The ability to produce methanethiol in urine after eating asparagus was once thought to be a genetic trait. However recent research suggests that the peculiar odor is in fact produced by all humans after consuming asparagus, while the ability to detect it (methanethiol being one of many components in "asparagus pee") is in fact the genetic trait. The chemical components responsible for the change in the odor of urine show as soon as 15 minutes after eating asparagus.
Violent reaction with strong oxidizers, bleaches, copper, nickel and their alloys; aluminum. Reacts with acids producing flammable and toxic hydrogen sulfide
Return refillable compressed gas cylinders to supplier. 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. Incineration followed by effective scrubbing of the effluent gas.
METHYL MERCAPTAN Preparation Products And Raw materials
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