Methyl isocyanate(MIC) is anorganic compoundwith the molecular formula CH3NCO. Synonyms areisocyanatomethaneandmethyl carbylamine.Methyl isocyanate is an intermediate chemical in the production ofcarbamatepesticides(such ascarbaryl,carbofuran,methomyl,andaldicarb). It has also been used in the production ofrubbersandadhesives.As an extremelytoxicand irritating compound, it is very hazardous to human health. MIC was the principal toxicant involved in theBhopal gas disaster,which short-term killed 4,000–8,000 people and caused permanent injury and premature deaths to tens of thousands more.[6][7][8][9][10]It is also a very potentlachrymatory agent.[11]
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Names | |
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Preferred IUPAC name
Isocyanatomethane | |
Other names
Methyl carbylamine
MIC | |
Identifiers | |
3D model (JSmol)
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ChEBI | |
ChemSpider | |
ECHA InfoCard | 100.009.879 |
PubChemCID
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UNII | |
CompTox Dashboard(EPA)
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Properties | |
C2H3NO | |
Molar mass | 57.051 g/mol |
Appearance | Colorless liquid |
Odor | Sharp, pungent odor[1] |
Density | 0.9230 g/cm3at 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 | 57.7kPa |
Structure | |
2.8D | |
Thermochemistry | |
Std enthalpy of
formation(ΔfH⦵298) |
−92.0kJ·mol−1[2] |
Std enthalpy of
combustion(ΔcH⦵298) |
-1.1275E+06J/mol[3] |
Hazards | |
GHSlabelling: | |
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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) | |
Flash point | −7 °C (19 °F; 266 K) |
534 °C (993 °F; 807 K) | |
Explosive limits | 5.3–26%[2] |
Lethal doseor concentration (LD, LC): | |
LD50(median dose)
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120 mg/kg (oral, mouse) 51.5 mg/kg (oral, rat)[4] |
LC50(median concentration)
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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)
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TWA 0.02 ppm (0.05 mg/m3) [skin][1] |
REL(Recommended)
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TWA 0.02 ppm (0.05 mg/m3) [skin][1] |
IDLH(Immediate danger)
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3 ppm[1] |
Related compounds | |
Related compounds
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Methyl isothiocyanate |
Except where otherwise noted, data are given for materials in theirstandard state(at 25 °C [77 °F], 100 kPa).
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Physical properties
editMethyl isocyanate is a colorless, poisonous,lachrymatory(tearingagent), flammable liquid.[12]It is soluble in water to 6–10 parts per 100 parts, but it also reacts with water (seeReactionsbelow).
It has a refractive index of 1.363 with a wavelength of 589 nm at a temperature of 20 °C[13]
Manufacture
editMethyl isocyanate is usually manufactured by the reaction ofmonomethylamineandphosgene.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 ofhydrogen chlorideis formed, but N-methylcarbamoyl chloride (MCC) forms as the mixture is condensed, leaving onemoleofhydrogen chlorideas a gas.
The methyl isocyanate is obtained by treating the MCC with atertiary amine,such asN,N-dimethylaniline,or withpyridine,[14]or by separating it by usingdistillationtechniques.[15]
Methyl isocyanate is also manufactured fromN-methylformamideand air. In the latter process, it is immediately consumed in a closed-loop process to makemethomyl.[16]Other manufacturing methods have been reported.[17][18]
Reactions
editMethyl isocyanate reacts readily with many substances that contain N-H or O-H groups. With water, it forms1,3-dimethylureaandcarbon dioxidewith 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.[19]
At 25 °C, in excess water, half of the MIC is consumed in 9 min.;[20]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 theBhopal disasterafter a large amount of water was introduced to a MIC storage tank. The consequence of the out of controlexothermic processwas arunaway reactionand the direct release of 42 tons of MIC to the atmosphere.
If MIC is in excess,1,3,5-trimethylbiuretis formed along withcarbon dioxide.[12]Alcoholsandphenols,which contain an O-H group, react slowly with MIC, but the reaction can be catalyzed by trialkylaminesor dialkyltin dicarboxylate.Oximes,hydroxylamines,andenolsalso react with MIC to form methylcarbamates.[12]These reactions produce the products described below (Uses).
Ammonia,primary, and secondaryaminesrapidly react with MIC to form substitutedureas.Other N-H compounds, such as amides andureas,react much more slowly with MIC.[21]
It also reacts with itself to form a trimer or higher-molecular-weight polymers. In the presence ofcatalysts,MIC reacts with itself to form a solid trimer, trimethyl isocyanurate, or a higher-molecular-weight polymer:
Sodium methoxide,triethyl phosphine,ferric chlorideand 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 isexothermic(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 trimethylisocyanurate.Sincecatalyticmetal salts can be formed from impurities in commercial grade MIC and steel, this product must not be stored in steel drums or tanks.[12]
Toxicity
editMethyl isocyanate is extremelytoxic.There is no knownantidote.The threshold limit value set by the American Conference of Governmental Industrial Hygienists is 0.02ppm.MIC is toxic by inhalation, ingestion and contact in quantities as low as 0.4ppm.Exposure symptoms include coughing,chestpain,dyspnea,asthma,irritation of theeyes,noseandthroat,as well asskindamage. Higher levels of exposure, over 21 ppm, can result in pulmonary or lungedema,emphysemaandhemorrhages,bronchialpneumoniaanddeath.Although the odor of methyl isocyanate cannot be detected at 5 ppm by most people, its potentlachrymalproperties 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).[11]
Proper care must be taken to store methyl isocyanate because of its ease of exothermically polymerizing (seeReactions) and its similar sensitivity to water. Onlystainless steelorglasscontainers 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 1984Bhopal disaster,when around 42,000 kilograms (93,000 lb) of methyl isocyanate and other gases were released from the underground reservoirs of theUnion 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.[22][23]
During structural fires, natural materials can contribute to releasing isocyanates including methyl isocyanate.[24]
Mechanism of action
editUntil recent decades, the mechanism of methyl isocyanate toxicity in humans was largely unknown or unclear.[25][26]Methyl isocyanate and otherisocyanatesareelectrophilesand are currently thought to cause toxicity by thealkylationof biomolecules.[27]The mechanism of methyl isocyanate was previously suspected to be thecarbamylationofhemoglobin,thus interfering with its oxygen-binding capability and causinghypoxia.However, experiments showed that whenratsandguinea pigswere exposed to methyl isocyanate atconcentrationsabove themedian 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.[28][29]
Extraterrestrial occurrence
editOn 30 July 2015, scientists reported that upon the first touchdown of thePhilaelander oncomet67/P'ssurface, measurements by theCOSAC and Ptolemy instrumentsrevealed sixteenorganic compounds,four of which were seen for the first time on acomet,includingacetamide,acetone,methyl isocyanate andpropionaldehyde.[31][32][33]
In 2017, two teams of astronomers using theAtacama Large Millimeter Array(ALMA)interferometermade of 66 radio telescopes in theAtacama Desert(northernChile) have discovered the presence of MIC around young Sun-like stars.[30]
MIC is considered aprebiotic moleculeas explained by the discoverers of the ALMA findings inIRAS 16293-2422,a multiple system of very young stars: "This family of organic molecules is involved in the synthesis ofpeptidesandamino acids,which, in the form ofproteins,are the biological basis for life as we know it ".[30]
References
edit- ^abcdeNIOSH Pocket Guide to Chemical Hazards."#0423".National Institute for Occupational Safety and Health(NIOSH).
- ^abcdLide, David R., ed. (2006).CRC Handbook of Chemistry and Physics(87th ed.). Boca Raton, FL:CRC Press.ISBN0-8493-0487-3.
- ^Lemoult (1898).Comptes Rendus Hebdomadaires des Séances de l'Académie des Sciences.126:43.
{{cite journal}}
:Missing or empty|title=
(help) - ^ab"Methyl isocyanate".Immediately Dangerous to Life or Health Concentrations (IDLH).National Institute for Occupational Safety and Health(NIOSH).
- ^"NFPA Hazard Rating Information for Common Chemicals".nmsu.edu. Archived fromthe originalon 17 February 2015.Retrieved10 June2021.
- ^Broughton E (May 2005)."The Bhopal disaster and its aftermath: a review".Environmental Health.4(1): 6.Bibcode:2005EnvHe...4....6B.doi:10.1186/1476-069X-4-6.PMC1142333.PMID15882472.
- ^Eckerman I (2001)."Chemical Industry and Public Health — Bhopal as an example"(PDF).MPH.2001(24). Göteborg, Sweden: Nordic School of Public Health.ISSN1104-5701.Archived(PDF)from the original on 30 October 2012.
- ^Eckerman I (2004).The Bhopal Saga - Causes and Consequences of the World's Largest Industrial Disaster.India: Universities Press.ISBN81-7371-515-7.Archived fromthe originalon 10 June 2007.
- ^Rosenberg J."At 1984 - Huge Poison Gas Leak in Bhopal, India".About.com.Archivedfrom the original on 2 December 2007.Retrieved10 July2008.
- ^Eckerman I (2013). "Bhopal Gas Catastrophe 1984: Causes and Consequences".Reference Module in Earth Systems and Environmental Sciences.Elsevier. pp. 272–287.doi:10.1016/B978-0-12-409548-9.01903-5.ISBN978-0-12-409548-9.
- ^abKimmerle G, Eben A (1964). "Zur Toxizität von Methylisocyanat und dessen quantitativer Bestimmung in der Luft".Archiv für Toxikologie.20(4): 235–241.doi:10.1007/bf00577897.S2CID21422558.
- ^abcdUnion Carbide Corporation "Methyl Isocyanate" Product Information Publication, F-41443, November 1967.
- ^Kirilin, Aleksei; Belova, Liya; Pletneva, Maria (January–February 2017). "New aspects of isocyanate synthesis with the use of O-silylurethanes".Mendeleev Communications.27(1): 99–100.doi:10.1016/j.mencom.2017.01.033.
- ^US patent 2480088,Slocombe, R. J.; Hardy, E. E., "Process of Producing Carbamyl Chlorides", issued 1949-08-23, assigned to Monsanto
- ^FR patent 1400863,Merz, W., "Procédé et dispositif de préparation d'isocyanates d'alkyle", issued 1965-05-28, assigned to Bayer
- ^Chemical Week,"A fleeting existence for toxic-gas molecules"p. 9, 12 June 1985.
- ^DE patent 2828259,Giesselmann, G.; Guenther, K.; Fuenten, W., "Verfahren zur Herstellung von Methyl Isocyanate", issued 1980-01-10, assigned to Degussa
- ^"A safer method for making carbamates".Chemical Week.1985b (20): 136. 1985.
- ^Manilla (2021). "Methyl isocyanate: Risk assessment, environmental, and health hazard".Hazardous Gases Risk Assessment on the Environment and Human Health:251–261.
- ^Castro EA, Moodie RB, Sansom PJ (1985). "The kinetics of hydrolysis of methyl and phenyl isocyanates".Journal of the Chemical Society, Perkin Transactions 2.1985(5): 737–742.doi:10.1039/P29850000737.
- ^March J (1985).Advanced Organic Chemistry(3rd ed.). New York: John Wiley & Sons. p. 802.
- ^Varma, Daya; Mulay, Shree (2015). "Methyl Isocyanate: The Bhopal Gas".Handbook of Toxicology of Chemical Warfare Agents:287–299.doi:10.1016/B978-0-12-800159-2.00022-1.
- ^"Bhopal trial: Eight convicted over India gas disaster".BBC News.7 June 2010.Archivedfrom the original on 7 June 2010.Retrieved7 June2010.
- ^Dzhordzhio Naldzhiev, Matija Strlic; Polyurethane insulation and household products – a systematic review of their impact on indoor environmental quality, [Building and Environmenthttps://www.sciencedirect.com/journal/building-and-environment], 2020
- ^Mehta PS, Mehta AS, Mehta SJ, Makhijani AB (December 1990). "Bhopal tragedy's health effects. A review of methyl isocyanate toxicity".JAMA.264(21): 2781–2787.doi:10.1001/jama.1990.03450210081037.PMID2232065.
- ^Varma DR (June 1987)."Epidemiological and experimental studies on the effects of methyl isocyanate on the course of pregnancy".Environmental Health Perspectives.72:153–157.doi:10.1289/ehp.8772153.PMC1474644.PMID3622430.
- ^Bessac, B.F.; Jordt, S.-E. (1 July 2010)."Sensory Detection and Responses to Toxic Gases: Mechanisms, Health Effects, and Countermeasures".Proceedings of the American Thoracic Society.7(4): 269–277.doi:10.1513/pats.201001-004sm.ISSN1546-3222.PMC3136963.PMID20601631.
- ^Varma, Daya R.; Guest, Ian (1993). "The Bhopal accident and methyl isocyanate toxicity".Journal of Toxicology and Environmental Health.40(4): 513–529.Bibcode:1993JTEH...40..513V.doi:10.1080/15287399309531816.ISSN0098-4108.PMID8277516.
- ^Ramachandran, P.K.; Gandhe, B.R.; Venkateswaran, K.S.; Kaushik, M.P.; Vijayaraghavan, R.; Agarwal, G.S.; Gopalan, N.; Suryanarayana, M.V.S.; Shinde, S.K.; Sriramachari, S. (1988). "Gas chromatographic studies of the carbamylation of haemoglobin by methyl isocyanate in rats and rabbits".Journal of Chromatography B: Biomedical Sciences and Applications.426(2): 239–247.doi:10.1016/s0378-4347(00)81952-0.ISSN0378-4347.PMID3392138.
- ^abc"ALMA Finds Ingredient of Life Around Infant Sun-like Stars".www.eso.org.Archivedfrom the original on 8 June 2017.Retrieved8 June2017.
- ^Jordans F (30 July 2015)."Philae probe finds evidence that comets can be cosmic labs".The Washington Post.Associated Press. Archived fromthe originalon 23 December 2018.Retrieved30 July2015.
- ^"Science on the Surface of a Comet".European Space Agency. 30 July 2015.Archivedfrom the original on 2 August 2015.Retrieved30 July2015.
- ^Bibring JP, Taylor MG, Alexander C, Auster U, Biele J, Finzi AE, et al. (July 2015)."Philae's first look. Philae's First Days on the Comet. Introduction"(PDF).Science.349(6247): 493.Bibcode:2015Sci...349..493B.doi:10.1126/science.aac5116.PMID26228139.
External links
edit- NIOSH Safety and Health Topic: Isocyanates,from the website of the National Institute for Occupational Safety and Health (NIOSH).
- U.S. National Library of Medicine: Hazardous Substances Databank – Methyl isocyanate