Isocyanates are prepared by thermal cleavage of urethanes, useful in the preparation of very pure aromatic di- and polyurethanes, which give a higher isocyanate yield than previous methods, without drying to very low moisture content

摘要

Preparation of isocyanate by thermal cleavage of the corresponding urethane in the steps: (a) preparation of urethane by reaction of the corresponding amine with urea and alcohol, (b) purification of the urethane by removal of the side products and impurities, (c) thermal cleavage of the urethane into isocyanate and alcohol, and (d) working up of the isocyanate is new. In purification of the urethane, components of the reaction mixture which are lower boiling than the urethane are distilled off, part of the urethane is removed from the reaction mixture by distillation under reduced pressure, the urethane is cleaved, the remaining sump fraction is heat treated in a rotary reactor, with cleavage of the urethane remaining in the sump fraction, and the isocyanate and alcohol cleavage products are drawn off as vapors.