|Molecular formula||C 2 H 3 NO|
colorless, tear-irritating liquid with a pungent odor
|External identifiers / databases|
|Molar mass||57.05 g · mol -1|
0.96 g cm −3
−45 ° C ° C
39.5 ° C
decomposes in water and alcohols
0.024 mg m −3
|ΔH f 0||
−92.0 kJ / mol
|As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C|
Methyl isocyanate ( MIC for short ) is the simplest ester of isocyanic acid . It is a very reactive chemical compound that z. B. is used in the manufacture of insecticides . Like isocyanic acid and the other isocyanates , it is very toxic.
On December 3, 1984, there was a serious chemical accident involving methyl isocyanate in Bhopal, India . In the process, between 25 and 40 tons of methyl isocyanate escaped from a defective tank in a pesticide factory owned by the American chemical company Union Carbide near the city. It is estimated that 3,800 to 25,000 people died as a result of this chemical accident. In addition, there was immense poisoning of the environment.
Up until spring 2011, these fabrics were also manufactured at Bayer AG's plant in Institute (West Virginia) . On January 11, 2011 Bayer announced that it would end MIC production at this plant, which was considered to be Bhopal's sister plant, by summer 2012. On February 10, 2011, a court in Charleston, West Virginia, upheld a lawsuit brought by 16 residents of Bayer's Institute facility and provisionally banned the production of the highly toxic chemical. Without waiting for the final verdict, Bayer management decided not to resume production.
Extraction and presentation
Technically methyl isocyanate by reaction of methyl amine and phosgene produced. After splitting off hydrogen chloride (HCl), the intermediate product N -methylcarbamoyl chloride is converted into methyl isocyanate:
In the first step, methylamine reacts at −20 ° C to 60 ° C with phosgene with elimination of HCl to form N -methylcarbamoyl chloride. In the second step at 100–200 ° C, methyl isocyanate is formed with renewed elimination of HCl.
Methyl isocyanate is a volatile, colorless liquid that is highly tear-inducing and, when concentrated, has a pungent odor. At slightly elevated temperatures (38 ° C), it goes into the gaseous aggregate state , at which they heavier than air is.
Methyl isocyanate forms highly flammable vapor-air mixtures. The compound has a flash point of approx. −35 ° C. The explosion range is between 5.3% by volume (126 g · m −1 ) as the lower explosion limit (LEL) and 26% by volume (618 g · m −1 ) as the upper explosion limit (UEL). The limit gap width was determined to be 1.21 mm (50 ° C). This results in an assignment to explosion group IIA. The ignition temperature is 530 ° C. The substance therefore falls into temperature class T1.
Methyl isocyanate is mainly used for the production of the carbamates aldicarb (Temik), carbofuran (Furadan), carbaryl (Sevin), methomyl and oxamyl . When reacted with alcohols , methyl carbamic acid esters are formed , with thiols methyl thiourethane .
The active ingredients carbaryl and aldicarb were produced in the pesticide factory of the American chemical company Union Carbide near the city of Bhopal .
A mechanism for the transport of methyl isocyanate in the body was discovered in 1992. According to this, glutathione , a tripeptide whose task is actually to protect the organism from damage by toxic substances, can reversibly add methyl isocyanate to the thiol group and thus transport it.
Methyl isocyanate causes burns of the mucous membranes , eyes and lungs when exposed , but severe burns of internal organs were also found in many of the victims of the Bhopal accident. This finding was surprising in that methyl isocyanate is too reactive to enter the cycle unchanged.
Methyl isocyanate is classified as potentially teratogenic.
- International Chemical Safety Card (ICSC) for methyl isocyanates at the National Institute for Occupational Safety and Health (NIOSH).
- Entry on methyl isocyanate. In: Römpp Online . Georg Thieme Verlag, accessed on May 4, 2014.
- Entry on methyl isocyanate in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
- David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Standard Thermodynamic Properties of Chemical Substances, pp. 5-22.
- City under the Shroud , one day Zeitgeschichten on SPIEGEL-Online , December 1, 2009.
- cbgnetwork.org: Bayer stops production of Bhopal chemical MIC ; January 12, 2010.
- bhopal.net: Bayer finally gives up toxic MIC production in Institute, WV , March 19, 2011.