Nitrogen halides reaction with, phosgene

A simpler non-phosgene process for the manufacture of isocyanates involves the reaction of amines with carbon dioxide (CO2) in the presence of an aprotic organic solvent and a nitrogenous base. The corresponding ammonium carbamate is treated with an electrophilic dehydrating agent [198, 282, 283]. This concept has been applied to the synthesis of several aromatic and ahphatic isocyanates. The process relies on the facile formation of amine<arbon dioxide salts using acid halides such as phosphoryl chloride and thionyl chloride [284, 285]. 

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