メタンチオール

外観

無色澄明の液体

性質

メチルメルカプタンは、有機硫黄化合物の1種で、特徴的な臭いを持つ物質です。メチルメルカプタンは無色の液体であり、沸点は6°C、融点は-123°Cです。水やエタノール、エーテルなどの極性溶媒に良好に溶ける一方、非極性溶媒には溶けにくい傾向があります。

メチルメルカプタンは還元性を持ち、空気中の酸素と反応して酸化されることがあります。また、酸と反応してメチルメルカプタン塩を生成することもあります。非常に強烈な不快な臭いを持ち、悪臭の原因物質です。この臭いは、カビや腐敗した食物、腐敗したタンパク質などからも発生することがあります。

また、他の有機化合物と反応して、硫黄化合物やチオエーテルなどの化合物を生成することがあります。また、ハロゲンとも反応し、ハロゲン化物を生成します。

これらの性質から、メチルメルカプタンは、ゴムやプラスチックの硫黄化剤、合成化学の中間体、医薬品の合成や、ガス漏れ検出用の添加剤などとして利用されます。

溶解性

水に難溶 (0.15g/100ml, 20℃), エタノール, エーテルに混和。エタノールと任意の割合で混和するが水に溶けない。

解説

メタンチオール メチルメルカプタンともいう．コールタール，石油蒸留物に含まれる．ヨウ化メチルと水硫化カリウムとの反応，チオ尿素にヨウ化メチルを反応させて得られるS-メチルチオウロニウム塩を，アルカリ分解して合成される．強い悪臭をもつ可燃性の気体．融点－126 ℃，沸点5.9 ℃．0.8665．水1 L に対する溶解度は23.30 g(20 ℃)．殺虫剤，殺菌剤，プラスチックの製造中間体やメチオニンの合成に使われる．悪臭防止法で指定されている悪臭物質．悪臭発生源はクラフトパルプ製造工場，獣畜の肉，皮，臓器などを原料として，皮革，油脂，にかわ，肥料，飼料などを製造する施設，魚腸骨処理場などである．LD50 10000 ppm(ラット)．

用途

メチオニンの原料、医薬品、殺虫剤、プラスチック、メチルチオエーテル触媒活性調整剤、ガス付臭剤、有機合成中間体、反応促進剤

用途

大気中等メチルメルカプタン(メタンチオール)のGC分析用標準液。

構造

メチルメルカプタンは、有機硫黄化合物の1種であり、メタン分子から1つの水素原子が硫黄原子に置換された構造をしています。この構造は、四面体構造をとっています。

チオール基はヒドロキシル基に比べて反応性が高く、特有の強烈な臭いがあります。メチルメルカプタンは、このチオール基を持つ最も単純な構造の化合物であり、他の有機硫黄化合物の基本構造です。

説明

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.

化学的特性

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.

物理的性質

Colorless gas with a garlic-like or rotten cabbage odor. An experimentally determined odor threshold concentration of 2.1 ppb_v was reported by Leonardos et al. (1969). A detection odor threshold concentration of 81 μg/m³ (41 ppb_v) was determined by Katz and Talbert (1930).

天然物の起源

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.

使用

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.

製造方法

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.

空気と水の反応

Highly flammable. Reacts with water, steam or acids to produce toxic, flammable vapors [Lewis].

反応プロフィール

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].

危険性

Flammable, dangerous fire risk. Explosive limits in air 3.9–21.8%. Strong irritant. Liver damage.

健康ハザード

Can cause death by respiratory paralysis. It is an eye and respiratory tract irritant. Exposure results in pulmonary edema and hepatic and renal damage.

火災危険

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.

使用用途

メチルメルカプタンは、メチオニンの原料として用いられています。メチオニンは、必須アミノ酸の1つであり、体内においてやに変換されます。これらによるの分解、あるいは免疫の増強作用が報告されています。

また、プラスチックやメチルチオエーテル触媒活性調整剤、有機合成中間体、反応促進剤、医薬品、殺虫剤、ジェット燃料、の試薬に用いられています。このほか、ガスが漏れたことを感知しやすくするために、ガス付臭剤として無臭のガスに添加される場合もあります。

安全性プロファイル

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.

職業ばく露

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.

製造方法

メチルメルカプタンの製造方法には、いくつかの方法が存在しますが、特に一般的なものは以下の2つです。

1. チオアセトンを原料に用いる反応
この方法では、チオアセトンと、強力な還元剤である水素化アルミニウムリチウムを用いて、チオアセトンのカルボニル基を還元してチオール基に変換することでメチルメルカプタンを生成します。

環境運命予測

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).

輸送方法

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.

不和合性

Violent reaction with strong oxidizers, bleaches, copper, nickel and their alloys; aluminum. Reacts with acids producing flammable and toxic hydrogen sulfide

廃棄物の処理

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.