Alkylation of nitrocyanamide. A new synthesis of isocyanates

Abstract

Thirteen alkyl halides (primary, secondary, and tertiary aliphatic including alicyclic, aralkyl, and heteroalkyl systems) and certain non-vicinal dihalides on treatment with silver nitrocyanamide are converted into the corresponding isocyanates (63–95%). Intermediate alkylnitrocyanamides, spectroscopically detected, thermolysed (–20–80 °C) to the expected isocyanates. In certain examples silver nitrocyanamide is generated in situ from sodium nitrocyanamide and silver nitrate. Silver nitrocyanamide does not react with cyclopropyl bromide, acetyl chloride, toluene-p-sulphonyl chloride, phenacyl bromide and 2-bromomethyldioxolane (27), and the ethylene acetal (28) of 1-bromo-4-iodopentacyclo[4.3.0.0^2,5.0^3,8.0^4,7]nonan-9-one. Silver nitrocyanamide reacts with 4,6-bis(bromomethyl)-3,7-dimethyl-1,5-diazabicyclo[3.3.0]octane-2,8-dione (26), to give an intractable mixture. Vicinal dihalides give erratic results without detectable formation of vicinal di-isocyanates: unisolated 2-bromoethyl isocyanate (tentative assignment) has been detected in a product mixture from ethylene dibromide; an expected rearrangement during the reaction with 1,2-dibromocyclobutane, brought about the formation of 4-bromobut-3-enyl isocyanate isolated as ethyl 4-bromobut-3-enylcarbamate in low yield; and 1,2-dibromocyclohexane gives 2-bromocyclohexyl isocyanate isolated as ethyl N-(2-bromocyclohexyl)carbamate in low yield.