Methyl isocyanate

Structural formula
General
Surname	Methyl isocyanate
other names	MIC; Isocyanatomethane; Isocyanic acid methyl ester;
Molecular formula	C 2 H 3 NO
Brief description	colorless, tear-irritating liquid with a pungent odor
External identifiers / databases
EC number	210-866-3
ECHA InfoCard	100,009,879
PubChem	12228
ChemSpider	11727
DrugBank	DB04337
Wikidata	Q410431
properties
Molar mass	57.05 g · mol -1
Physical state	liquid
density	0.96 g cm −3
Melting point	−45 ° C ° C
boiling point	39.5 ° C
Vapor pressure	464 h Pa (20 ° C); 710 hPa (30 ° C); 1050 hPa (40 ° C); 1510 hPa (50 ° C);
solubility	decomposes in water and alcohols
Refractive index	1.3637
safety instructions
H and P phrases	H: 225-361d-330-311-301-334-317-335-315-318
	P: ?
MAK	0.024 mg m −3
Toxicological data	71 mg kg −1 ( LD 50 , rat , oral )
Thermodynamic properties
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.

history

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.

properties

Physical Properties

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.

Chemical properties

When reacted with alcohols, methyl isocyanate reacts to form carbamates :

{\ displaystyle \ mathrm {CH_ {3} {-} N {=} C {=} O + R {-} OH \ longrightarrow CH_ {3} NH {-} CO {-} OR}}

With amines , methyl isocyanate can be converted into urea derivatives :

{\ displaystyle \ mathrm {CH_ {3} {-} N {=} C {=} O + (R ^ {1}) (R ^ {2}) NH \ longrightarrow}}

{\ displaystyle \ mathrm {CH_ {3} NH {-} CO {-} N (R ^ {1}) (R ^ {2}) \}}

Safety-related parameters

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.

use

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 .

physiology

Reaction of methyl isocyanate with glutathione

The direct toxicity of methyl isocyanate results from its ability to attack numerous nucleophilic groups of metabolically active biomolecules .

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.

safety instructions

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.

Web links

International Chemical Safety Card (ICSC) for methyl isocyanates at the National Institute for Occupational Safety and Health (NIOSH).

Individual evidence

↑ ^a ^b ^c ^d Entry on methyl isocyanate. In: Römpp Online . Georg Thieme Verlag, accessed on May 4, 2014.

↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ Entry on methyl isocyanate in the GESTIS substance database of the IFA , accessed on January 19, 2020(JavaScript required) .

↑ 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.

[roempp-1] Entry on methyl isocyanate. In: Römpp Online . Georg Thieme Verlag, accessed on May 4, 2014.

[GESTIS-2] ↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ Entry on methyl isocyanate in the GESTIS substance database of the IFA , accessed on January 19, 2020(JavaScript required) .

[CLP_100.009.879-3] 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 .

[CRC90_5_22-4] 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.

[5] City under the Shroud , one day Zeitgeschichten on SPIEGEL-Online , December 1, 2009.