Methyl isocyanate, from decomposition

This intermediate (or its ethyl homologue), produced dining the preparation of phosphoryl dichloride isocyanate from interaction of phosphorus pentachloride and methyl (or ethyl) carbamate, is unstable. Its decomposition to the required product may be violent or explosive unless moderated by presence of a halogenated solvent. 

Studies detailing the thermal and photochemical reactions of these compounds are rare. The l-oxa-2,4-diazine 63 is known, from H NMR, to be in equilibrium with the spiro isomer 64, with the former predominating. Heating this mixture above 40 °C results in decomposition to acetonitrile, methyl isocyanate, and benzene (Scheme 4) <1995H(40)619>. The formation of compounds such as 63 (and 64) by cycloaddition of nitrile oxides to 8-azahepta-fulvenes is discussed in Section 9.05.10. 

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