GENERATION OF URETHANES AND ISOCYANATES FROM AMINES AND CARBON-DIOXIDE

Use of carbon dioxide as a reagent in place of phosgene offers the potential for an inexpensive, safer, and more selective route to polyurethanes. Traditionally, isocyanates, which are used for the production of polyurethanes, are generated from the reaction of a primary amine with the highly toxic agent phosgene. The reaction of CO2 with either primary or secondary amines generates the carbamate anion. By understanding those factors which control the nucleophilicity of the carbamate anion, we have been able to generate urethanes quantitatively even with secondary amine-derived carbamate anions. We have also found that isocyanates can be generated quantitatively by the ''dehydration'' of carbamate anions derived from primary amines and carbon dioxide using a variety of dehydrating reagents. These processes are accomplished under very mild conditions; e. g., 1 atm CO2 at 50-80 degrees C. The factors which favor production of urethane or carbamate are discussed and examples of the utility of these new chemistries are presented.