Process for preparing isocyanates

A process for preparing an isocyanate comprising:

• (a) contacting CO.sub.2 and a primary amine in the presence of an aprotic organic solvent and a base selected from the group consisting of a phosphazene compound, an organic, nitrogenous base and mixtures thereof wherein said organic, nitrogenous base is selected from the group consisting of guanidine compounds, amidine compounds, tertiary amines, pyridine and mixtures thereof, under reaction conditions of time and temperature sufficient to produce the corresponding ammonium carbamate salt,
• (b) recovering said ammonium carbamate salt, and
• (c) reacting said ammonium carbamate salt with an electrophilic or oxophilic dehydrating agent selected from the group consisting of anhydrides having the formulas:
• ##STR22## thioanhydrides having the formula:
• ##STR23## and mixtures thereof wherein X and Y are independently selected from the group consisting of ##STR24## R.sub.5 and R.sub.6 are independently selected from the group consisting of alkyl, fluoroalkyl, aryl, alkaryl and aralkyl radicals having 1 to about 22 carbon atoms, or R.sub.5 and R.sub.6 together form a cyclic thioanhydride containing a fused aromatic or cycloaliphatic ring in the presence of an aprotic organic solvent and a base selected from the group consisting of a phosphazene compound, an organic, nitrogenous base and mixtures thereof, wherein said organic, nitrogenous base is selected from the group consisting of guanidine compounds, amidine compounds, tertiary amines, pyridine and mixtures thereof, at a temperature of -78.degree. C. to 100.degree. C. and a time sufficient to produce the corresponding isocyanate.