Methyl Isocyanate
Title: Methyl Isocyanate
CAS Registry Number: 624-83-9
CAS Name: Isocyanatomethane
Additional Names: isocyanic acid methyl ester; MIC
Molecular Formula: C2H3NO
Molecular Weight: 57.05
Percent Composition: C 42.11%, H 5.30%, N 24.55%, O 28.04%
Line Formula: CH3N=C=O
Literature References: Intermediate in the manufacture of insecticides and herbicides including carbaryl, q.v. Prepn via Curtius rearrangement: J. W. Boehmer, Rec. Trav. Chim. 55, 379 (1933); by heating N,N-diphenyl-N¢-methylurea: W. Siefken, Ann. 562, 75 (1949); by phosgenation of bis(trimethylsilyl)methylamine: V. F. Mironov et al., Zh. Obshch. Khim. 39, 2598 (1969). Used in prepn of a-aryl-b-methylureas: J. W. Boehmer, loc. cit.; of semicarbazides: Ch. C. P. Pacilly, Rec. Trav. Chim. 55, 101 (1936); in conversion of aldoximes to nitriles: J. A. Albright, M. L. Alexander, Org. Prep. Proced. Int. 4, 215 (1972). Toxicity of vapor to rats, mice, humans; physical properties: G. Kimmerle, A. Eben, Arch. Toxicol. 20, 235 (1960). Uptake and distribution studies in animals: J. S. Ferguson et al., Toxicol. Appl. Pharmacol. 94, 104 (1988). Acute oral toxicity: E. H. Vernot et al., ibid. 42, 417 (1977).
Properties: Liquid, bp 39-40°. d20 0.96. Vapor press. at 4.2°: 200 torr; at 13.5°: 300 torr; at 20.6°: 400 torr; at 31.2°: 600 torr. LD50 in male rats (mg/kg): 140 single oral dose (Vernot). LC50 in rats (4 hours exposure to vapor): 5 ppm (Kimmerle, Eben).
Boiling point: bp 39-40°
Density: d20 0.96
Toxicity data: LD50 in male rats (mg/kg): 140 single oral dose (Vernot); LC50 in rats (4 hours exposure to vapor): 5 ppm (Kimmerle, Eben)
NOTE: An industrial accident during the manufacture of carbaryl in Bhopal, India on December 3, 1984 resulted in the leakage of an unknown amount of methyl isocyanate into the air. Over 2,000 people died and an estimated 200,000 were exposed to the vapor: Chem. Eng. News 62, 6 (Dec. 10, 1984); ibid. 63, 14 (Feb. 11, 1985). Series of articles on follow-up studies on survivors: Indian J. Exp. Biol. 26, 149-176, 201-204 (1988). Review of human toxicity: P. S. Mehta et al., J. Am. Med. Assoc. 264, 2781-2787 (1990).
CAUTION: Potential symptoms of overexposure are irritation of eyes, skin, nose and throat; respiratory sensitization; coughing, pulmonary secretions, chest pain and dyspnea; asthma; eye and skin injury. See NIOSH Pocket Guide to Chemical Hazards (DHHS/NIOSH 97-140, 1997) p 212. Highly volatile. Exposure to 2 ppm for 1-5 min produced tears and irritation of the nose and throat (Kimmerle, Eben).
Use: In organic synthesis; in manufacture of carbamate pesticides.

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