Methyl isocyanate

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Methyl isocyanate
Methyl isocyanate.svg
Methyl-isocyanate-3D-vdW.png
Names
Preferred IUPAC name
Isocyanatomethane
Other names
Methyl carbylamine
MIC
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.009.879 OOjs UI icon edit-ltr-progressive.svg
PubChem CID
UNII
  • InChI=1S/C2H3NO/c1-3-2-4/h1H3 Yes check.svgY
    Key: HAMGRBXTJNITHG-UHFFFAOYSA-N Yes check.svgY
  • O=C=NC
Properties
C2H3NO
Molar mass 57.051 g/mol
AppearanceColorless liquid
Odor Sharp, pungent odor [1]
Density 0.9230 g/cm3 at 27 °C
Melting point −45 °C (−49 °F; 228 K) [2]
Boiling point 38.3–41 °C (100.9–105.8 °F; 311.4–314.1 K) [2]
10% (15°C) [1]
Vapor pressure 57.7 kPa
Structure
2.8 D
Thermochemistry
−92.0 kJ·mol−1 [2]
-1.1275E+06 J/mol [3]
Hazards
GHS labelling:
GHS-pictogram-skull.svg GHS-pictogram-silhouette.svg GHS-pictogram-flamme.svg GHS-pictogram-acid.svg GHS-pictogram-exclam.svg
H225, H300, H311, H315, H317, H318, H330, H334, H335, H361d
P201, P202, P210, P233, P240, P241, P242, P243, P260, P261, P264, P270, P271, P272, P280, P281, P284, P285, P301+P310, P302+P352, P303+P361+P353, P304+P340, P304+P341, P305+P351+P338, P308+P313, P310, P312, P320, P321, P322, P330, P332+P313, P333+P313, P342+P311, P361, P362, P363, P370+P378, P403+P233, P403+P235, P405, P501
NFPA 704 (fire diamond)
NFPA 704.svgHealth 4: Very short exposure could cause death or major residual injury. E.g. VX gasFlammability 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g. gasolineInstability 3: Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked. E.g. hydrogen peroxideSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g. sodium, sulfuric acid
4
3
3
W
Flash point −7 °C (19 °F; 266 K)
534 °C (993 °F; 807 K)
Explosive limits 5.3–26% [2]
Lethal dose or concentration (LD, LC):
120 mg/kg (oral, mouse)
51.5 mg/kg (oral, rat) [4]
6.1 ppm (rat, 6 hr)
12.2 ppm (mouse, 6 hr)
5.4 ppm (guinea pig, 6 hr)
21 ppm (rat, 2 hr) [4]
NIOSH (US health exposure limits):
PEL (Permissible)
TWA 0.02 ppm (0.05 mg/m3) [skin] [1]
REL (Recommended)
TWA 0.02 ppm (0.05 mg/m3) [skin] [1]
IDLH (Immediate danger)
3 ppm [1]
Related compounds
Related compounds
 Methyl isothiocyanate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

Methyl isocyanate (MIC) is an organic compound with the molecular formula CH3NCO. Synonyms are isocyanatomethane and methyl carbylamine. Methyl isocyanate is an intermediate chemical in the production of carbamate pesticides (such as carbaryl, carbofuran, methomyl, and aldicarb). It has also been used in the production of rubbers and adhesives. As an extremely toxic and irritating compound, it is very hazardous to human health. MIC was the principal toxicant involved in the Bhopal gas disaster, which eventually killed around 20,000 people in total as per official figures. [6] [7] [8] [9] [10] [11] [12] It is also a very potent lachrymatory agent.

Physical properties

Methyl isocyanate is a colorless, poisonous, lachrymatory (tearing agent), flammable liquid. [13] It is soluble in water to 6–10 parts per 100 parts, but it also reacts with water (see Reactions below).

It has a refractive index of 1.363 with a wavelength of 589 nm at a temperature of 20 °C [14]

Manufacture

Methyl isocyanate is usually manufactured by the reaction of monomethylamine and phosgene. For large-scale production it is advantageous to combine these reactants at higher temperature in the gas phase. A mixture of methyl isocyanate and two moles of hydrogen chloride is formed, but N-methylcarbamoyl chloride (MCC) forms as the mixture is condensed, leaving one mole of hydrogen chloride as a gas.

MMA plus Phosgene diagram.svg

The methyl isocyanate is obtained by treating the MCC with a tertiary amine, such as N,N-dimethylaniline, or with pyridine, [15] or by separating it by using distillation techniques. [16]

MCC to MIC & HCl.svg

Methyl isocyanate is also manufactured from N-methylformamide and air. In the latter process, it is immediately consumed in a closed-loop process to make methomyl. [17] Other manufacturing methods have been reported. [18] [19]

Reactions

Methyl isocyanate reacts readily with many substances that contain N-H or O-H groups. With water, it forms 1,3-dimethylurea and carbon dioxide with the evolution of heat (1358.5 joules, or 325 calories, per gram of MIC): It is relatively slow to react at below 68 °F, but will increase its rate with elevated temperatures or in the presence of acid or base. [20]

MIC & water to DMU & TMB.png

At 25 °C, in excess water, half of the MIC is consumed in 9 min.; [21] if the heat is not efficiently removed from the reacting mixture, the rate of the reaction will increase and rapidly cause the MIC to boil. Such a reaction triggered the Bhopal disaster after a large amount of water was introduced to a MIC storage tank. The consequence of the out of control exothermic process was a runaway reaction and the direct release of 42 tons of MIC to the atmosphere.

If MIC is in excess, 1,3,5-trimethylbiuret is formed along with carbon dioxide. [13] Alcohols and phenols, which contain an O-H group, react slowly with MIC, but the reaction can be catalyzed by trialkylamines or dialkyltin dicarboxylate. Oximes, hydroxylamines, and enols also react with MIC to form methylcarbamates. [13] These reactions produce the products described below (Uses).

MIC plus 1-naphthol to carbaryl.svg

Ammonia, primary, and secondary amines rapidly react with MIC to form substituted ureas. Other N-H compounds, such as amides and ureas, react much more slowly with MIC. [22]

It also reacts with itself to form a trimer or higher-molecular-weight polymers. In the presence of catalysts, MIC reacts with itself to form a solid trimer, trimethyl isocyanurate, or a higher-molecular-weight polymer:

MIC to trimer.svg

Sodium methoxide, triethyl phosphine, ferric chloride and certain other metal compounds catalyze the formation of the MIC-trimer, while the high-molecular-weight polymer formation is catalyzed by certain trialkylamines. Since the formation of the MIC trimer is exothermic (1246 joules, or 298 calories, per gram of MIC), the reaction can lead to violent boiling of the MIC. The high-molecular-weight polymer hydrolyzes in hot water to form the trimethyl isocyanurate. Since catalytic metal salts can be formed from impurities in commercial grade MIC and steel, this product must not be stored in steel drums or tanks. [13]

Toxicity

Methyl isocyanate is extremely toxic. There is no known antidote. The threshold limit value set by the American Conference of Governmental Industrial Hygienists is 0.02 ppm. MIC is toxic by inhalation, ingestion and contact in quantities as low as 0.4 ppm. Exposure symptoms include coughing, chest pain, dyspnea, asthma, irritation of the eyes, nose and throat, as well as skin damage. Higher levels of exposure, over 21 ppm, can result in pulmonary or lung edema, emphysema and hemorrhages, bronchial pneumonia and death. Although the odor of methyl isocyanate cannot be detected at 5 ppm by most people, its potent lachrymal properties provide an excellent warning of its presence (at a concentration of 2–4 parts per million (ppm) subjected to eyes are irritated, while at 21 ppm, subjects could not tolerate the presence of methyl isocyanate in air). [23]

Proper care must be taken to store methyl isocyanate because of its ease of exothermically polymerizing (see Reactions) and its similar sensitivity to water. Only stainless steel or glass containers may be safely used; the MIC must be stored at temperatures below 40 °C (104 °F) and preferably at 4 °C (39 °F).[ citation needed ]

The toxic effect of the compound was apparent in the 1984 Bhopal disaster, when around 42,000 kilograms (93,000 lb) of methyl isocyanate and other gases were released from the underground reservoirs of the Union Carbide India Limited (UCIL) factory, over a populated area on 3 December 1984, killing about 3,500 people immediately, 8,000 people in the first 48 hours and 15,000 more over the next several years. 200,000 people had lasting health effects from the disaster. [24] [25]

During structural fires, natural materials can contribute to releasing isocyanates including methyl isocyanate. [26]

Mechanism of action

Until recent decades, the mechanism of methyl isocyanate toxicity in humans was largely unknown or unclear. [27] [28] Methyl isocyanate and other isocyanates are electrophiles and are currently thought to cause toxicity by the alkylation of biomolecules. [29] The mechanism of methyl isocyanate was previously suspected to be the carbamylation of hemoglobin, thus interfering with its oxygen-binding capability and causing hypoxia. However, experiments showed that when rats and guinea pigs were exposed to methyl isocyanate at concentrations above the median lethal concentration (LC50, the concentration sufficient to kill 50% of the tested population), only 2% of hemoglobin molecules were carbamylated, suggesting that this is probably not the mechanism of toxicity. [30] [31]

Extraterrestrial occurrence

A photographic montage of methyl isocyanate around young Sun-like stars, as detected by the ALMA interferometer (northern Chile). ALMA detects methyl isocyanate around young Sun-like stars.jpg
A photographic montage of methyl isocyanate around young Sun-like stars, as detected by the ALMA interferometer (northern Chile).

On 30 July 2015, scientists reported that upon the first touchdown of the Philae lander on comet 67/P 's surface, measurements by the COSAC and Ptolemy instruments revealed sixteen organic compounds, four of which were seen for the first time on a comet, including acetamide, acetone, methyl isocyanate and propionaldehyde. [33] [34] [35]

In 2017, two teams of astronomers using the Atacama Large Millimeter Array (ALMA) interferometer made of 66 radio telescopes in the Atacama Desert (northern Chile) have discovered the presence of MIC around young Sun-like stars. [32]

MIC is considered a prebiotic molecule as explained by the discoverers of the ALMA findings in IRAS 16293-2422, a multiple system of very young stars: "This family of organic molecules is involved in the synthesis of peptides and amino acids, which, in the form of proteins, are the biological basis for life as we know it". [32]

Related Research Articles

<span class="mw-page-title-main">Phosgene</span> Toxic gaseous compound (COCl2)

Phosgene is an organic chemical compound with the formula COCl2. It is a toxic, colorless gas; in low concentrations, its musty odor resembles that of freshly cut hay or grass. It can be thought of chemically as the double acyl chloride analog of carbonic acid, or structurally as formaldehyde with the hydrogen atoms replaced by chlorine atoms. Phosgene is a valued and important industrial building block, especially for the production of precursors of polyurethanes and polycarbonate plastics.

<span class="mw-page-title-main">Isocyanate</span> Chemical group (–N=C=O)

In organic chemistry, isocyanate is the functional group with the formula R−N=C=O. Organic compounds that contain an isocyanate group are referred to as isocyanates. An organic compound with two isocyanate groups is known as a diisocyanate. Diisocyanates are manufactured for the production of polyurethanes, a class of polymers.

<span class="mw-page-title-main">Bhopal disaster</span> 1984 gas-leak accident in Bhopal, India

The Bhopal disaster or Bhopal gas tragedy was a chemical accident on the night of 2–3 December 1984 at the Union Carbide India Limited (UCIL) pesticide plant in Bhopal, Madhya Pradesh, India. In what is considered the world's worst industrial disaster, over 500,000 people in the small towns around the plant were exposed to the highly toxic gas methyl isocyanate (MIC). Estimates vary on the death toll, with the official number of immediate deaths being 2,259. In 2008, the Government of Madhya Pradesh paid compensation to the family members of 3,787 victims killed in the gas release, and to 574,366 injured victims. A government affidavit in 2006 stated that the leak caused 558,125 injuries, including 38,478 temporary partial injuries and approximately 3,900 severely and permanently disabling injuries. Others estimate that 8,000 died within two weeks, and another 8,000 or more have since died from gas-related diseases.

<span class="mw-page-title-main">Phosphine</span> Chemical compound hydrogen phosphide

Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula PH3, classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting fish, due to the presence of substituted phosphine and diphosphane (P2H4). With traces of P2H4 present, PH3 is spontaneously flammable in air (pyrophoric), burning with a luminous flame. Phosphine is a highly toxic respiratory poison, and is immediately dangerous to life or health at 50 ppm. Phosphine has a trigonal pyramidal structure.

Chloromethane, also called methyl chloride, Refrigerant-40, R-40 or HCC 40, is an organic compound with the chemical formula CH3Cl. One of the haloalkanes, it is a colorless, sweet-smelling, flammable gas. Methyl chloride is a crucial reagent in industrial chemistry, although it is rarely present in consumer products, and was formerly utilized as a refrigerant. Most chloromethane is biogenic.

<span class="mw-page-title-main">Vinyl chloride</span> Chemical compound

Vinyl chloride is an organochloride with the formula H2C=CHCl. It is also called vinyl chloride monomer (kịt) or chloroethene. This colorless compound is an important industrial chemical chiefly used to produce the polymer, poly(vinyl chloride) (PVC). Vinyl chloride monomer is among the top twenty largest petrochemicals (petroleum-derived chemicals) in world production. The United States remains the largest vinyl chloride manufacturing region because of its low-production-cost position in chlorine and ethylene raw materials. China is also a large manufacturer and one of the largest consumers of vinyl chloride. Vinyl chloride is a flammable gas that has a sweet odor and is carcinogenic. It can be formed in the environment when soil organisms break down chlorinated solvents. Vinyl chloride that is released by industries or formed by the breakdown of other chlorinated chemicals can enter the air and drinking water supplies. Vinyl chloride is a common contaminant found near landfills. Before the 1970s, vinyl chloride was used as an aerosol propellant and refrigerant.

<span class="mw-page-title-main">Carbaryl</span> Chemical compound

Carbaryl is a chemical in the carbamate family used chiefly as an insecticide. It is a white crystalline solid previously sold under the brand name Sevin, which was a trademark of the Bayer Company. The Sevin trademark has since been acquired by GardenTech, which has eliminated carbaryl from most Sevin formulations. Union Carbide discovered carbaryl and introduced it commercially in 1958. Bayer purchased Aventis CropScience in 2002, a company that included Union Carbide pesticide operations. Carbaryl was the third-most-used insecticide in the United States for home gardens, commercial agriculture, and forestry and rangeland protection. As a veterinary drug, it is known as carbaril (INN).

Cyanogen chloride is a highly toxic chemical compound with the formula CNCl. This linear, triatomic pseudohalogen is an easily condensed colorless gas. More commonly encountered in the laboratory is the related compound cyanogen bromide, a room-temperature solid that is widely used in biochemical analysis and preparation.

<span class="mw-page-title-main">Methylamine</span> Organic chemical compound

Methylamine is an organic compound with a formula of CH3NH2. This colorless gas is a derivative of ammonia, but with one hydrogen atom being replaced by a methyl group. It is the simplest primary amine.

<span class="mw-page-title-main">Phosphorus trichloride</span> Chemical compound

Phosphorus trichloride is an inorganic compound with the chemical formula PCl3. A colorless liquid when pure, it is an important industrial chemical, being used for the manufacture of phosphites and other organophosphorus compounds. It is toxic and reacts readily with water to release hydrogen chloride.

A chemical accident is the unintentional release of one or more hazardous chemicals, which could harm human health and the environment. Such events include fires, explosions, and release of toxic materials that may cause people illness, injury, or disability. Chemical accidents can be caused for example by natural disasters, human error, or deliberate acts for personal gain. Chemical accidents are generally understood to be industrial-scale ones, often with important offsite consequences. Unintended exposure to chemicals that occur at smaller work sites, as well as in private premises during everyday activities are usually not referred to as chemical accidents.

Union Carbide India Limited (UCIL) was a chemical company founded in 1934. UCIL employed 9,000 people. UCIL was 50.9% owned by Union Carbide and Carbon Corporation (UCC) located in the United States and 49.1% by Indian investors including the Government of India and government-controlled banks. UCIL produced batteries, carbon products, welding equipment, plastics, industrial chemicals, pesticides and marine products. A UCIL facility located in Bhopal, Madhya Pradesh was responsible for manufacturing various chemical products this primarily included pesticides. In 1984, a gas leak happened at the UCIL plant in Bhopal, killing thousands of people, and harming victims by causing chronic illness. At the time of the disaster, UCIL was ranked twenty-first in size among companies operating in India. It had revenues of ₹2 billion.

<span class="mw-page-title-main">Isophorone diisocyanate</span> Chemical compound

Isophorone diisocyanate (IPDI) is an organic compound in the class known as isocyanates. More specifically, it is an aliphatic diisocyanate. It is produced in relatively small quantities, accounting for only 3.4% of the global diisocyanate market in the year 2000. Aliphatic diisocyanates are used, not in the production of polyurethane foam, but in special applications, such as enamel coatings which are resistant to abrasion and degradation from ultraviolet light. These properties are particularly desirable in, for instance, the exterior paint applied to aircraft.

<span class="mw-page-title-main">Hexachloroethane</span> Chemical compound

Hexachloroethane (perchloroethane) is an organochlorine compound with the chemical formula (CCl3)2. It is a white or colorless solid at room temperature with a camphor-like odor. It has been used by the military in smoke compositions, such as base-eject smoke munitions.

A blowing agent is a substance which is capable of producing a cellular structure via a foaming process in a variety of materials that undergo hardening or phase transition, such as polymers, plastics, and metals. They are typically applied when the blown material is in a liquid stage. The cellular structure in a matrix reduces density, increasing thermal and acoustic insulation, while increasing relative stiffness of the original polymer.

The International Medical Commission on Bhopal (IMCB) was established in 1993 to organise medical responses to the 1984 Bhopal disaster (India).

<span class="mw-page-title-main">Ethenone</span> Organic compound with the formula H2C=C=O

In organic chemistry, ethenone is the formal name for ketene, an organic compound with formula C2H2O or H2C=C=O. It is the simplest member of the ketene class. It is an important reagent for acetylations.

α-Methylstyrene (AMS) is an organic compound with the formula C6H5C(CH3)=CH2. It is a colorless oil.

<span class="mw-page-title-main">Chloroacetaldehyde</span> Chemical compound

Chloroacetaldehyde is an organic compound with the formula ClCH2CHO. Like some related compounds, it is highly electrophilic reagent and a potentially dangerous alkylating agent. The compound is not normally encountered in the anhydrous form, but rather as the hemiacetal (ClCH2CH(OH))2O.

<span class="mw-page-title-main">Trifluoroacetyl chloride</span> Chemical compound

Trifluoroacetyl chloride (also known as TFAC) is a toxic gaseous chemical compound with the chemical formula C2ClF3O. TFAC is the perfluorinated version of acetyl chloride. The compound is a gas, but it is usually shipped as a liquid under high pressure.

References

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  2. 1 2 3 4 Lide, David R., ed. (2006). CRC Handbook of Chemistry and Physics (87th ed.). Boca Raton, FL: CRC Press. ISBN   0-8493-0487-3.
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