Methyl Isocyanate

CAS RN: 624-83-9

Reactivities / Incompatibilities

Reacts with water, which may cause runaway reaction ...
The underlying cause of the disastrous release of methyl isocyanate at Bhopal in December 1984 which caused over 2000 fatalities is not certain ... However, it seems probable that an exothermic reaction in one of the three 13 cu m methyl isocyanate storage vessels had raised the internal temp to above the boiling point (39 deg C), and that the continuing exotherm was beyond the capabilities of the cooling system to prevent a further substantial increase in pressure, which was eventually relieved through the emergency alkali scrubber and flare stack system. Unfortunately the partially inoperative scrubbing system could not deal with the rapid vapor release, and the flare system failed to ignite, so that of the 35 tons of isocyanate in the tank, some 23 tons were released during the 2 hr the safety valve was open. The origin of the exothermic reaction was not clear at the time, but it was known that alkyl isocyanates would trimerize to trialkyl isocyanurates in the presence of various catalysts, would react with amines to form alkylureas, and were hydrolyzed by water in presence of catalytic amt of acids or bases, with evolution of carbon dioxide. Contamination of the storage bessel(s) by moisture, methylamine or acidic or metallic impurities (possibly introduced via the nitrogen inerting system) may be the most likely underlying cause(s) of the disaster. The key role of water has now been confirmed. The Union Carbide report on the probable causes and course of the Bhopal disaster has been summarized. Analysis of the residue in the ruptured tank led to proposal of a mechanism, involving both water and chloroform as contaminants, to account for the detailed composition of the residue. A detailed analysis of the many factors and failings which led to the ingress of water into the storage rank and to the subsequent disastrous large-scale vapor release has been presented. The probable number of fatalities is given as between 5 and 8 thousand.
Attacks some forms of plastic, rubber and coatings.
... Contact with water causes formation of carbon dioxide and methylamine gases. The reaction is much more rapid in the presence of acids, alkalies, and amines.
Contact with iron, tin, copper (or salts of these elements) and with certain other catalysts (such as triphenylarsenic oxide, triethylphosphine, and tributyltin oxide) may cause violent polymerization and produce hazardous decomposition products: toxic gases and vapors (such as hydrogen cyanide, oxides of nitrogen, and carbon monoxide) may be released in a fire involving methyl isocyanate.
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