Everything about Methyl Isocyanate totally explained
Methyl isocyanate (MIC) is an organic compound with the molecular formula C
2H
3NO, arranged as H
3C-N=C=O. Synonyms are isocyanatomethane, methyl carbylamine, and MIC. It was discovered in 1888 as an
ester of
isocyanic acid. 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 a highly
toxic and irritating material, it's hazardous to human health, and was involved in the
Bhopal disaster which killed nearly 3,800 people.
Physical properties
Methyl isocyanate (MIC) is a clear, colorless,
lachrymatory, sharp smelling liquid. It is highly flammable, boils at 39.1 °C and has a low
flash point. Methyl isocyanate is soluble in water to 6-10 parts per 100 parts, but it reacts with the water (see
Reactions).
Manufacture
Methyl isocyanate is usually manufactured from
monomethylamine and
phosgene. These substances react at a range of temperatures, but for large scale production it's 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 and leaves one
mole of hydrogen chloride as a gas.
The methyl isocyanate is obtained by treating the MCC with a tertiary amine (e. g.:
dimethylaniline,
pyridine or by separating it by using distillation techniques.
Methyl isocyanate is also manufactured from N-methylformamide and air. In the latter process it's immediately consumed in a closed-loop process to make methomyl. Other manufacturing methods have been reported.
Reactions
Methyl isocyanate reacts readily with many substances that contain N-H or O-H groups and some other compounds. It also reacts with itself to form a trimer or higher molecular weight polymers.
Methyl isocyanate reacts with water to form
1,3-dimethylurea and
carbon dioxide with the evolution of heat (325 calories per gram of MIC that reacts).
At 25 °C, in excess water, one-half of the MIC is consumed in 9 minutes; if the heat isn't efficiently removed from the mixture the rate of the reaction will increase and rapidly cause the MIC to boil. If MIC is in excess,
1,3,5-trimethylbiuret is formed along with
carbon dioxide.
Alcohols and
phenols, which contain an O-H group, react slowly with MIC, but the reaction can be catalyzed by trialkyl
amines or dialkyltin dicarboxylate.
Oximes,
hydroxylamines, and
enols also react with MIC to form methylcarbamates.
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.
The toxic effect of the compound was apparent in the
Bhopal disaster, when around 43,000
kilograms of methyl isocyanate and other gases were released over a populated area on
December 3,
1984, immediately killing thousands and leading to the deaths of tens of thousands in subsequent weeks and months.
Further Information
Get more info on 'Methyl Isocyanate'.
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