Preparation of monoisocyanates from isocyanate distillation residues

Monoisocyanates are made by heating N,N1-disubstituted ureas, monosubstituted ureas or primary amines at 150-300 DEG C. with the distillation residues containing NCO groups formed in the production of isocyanates from amines and phosgene. The monoisocyanates are distilled off from the reaction mixture. It is preferred to use less than the stoichiometric amount of urea or amine based on NCO content of the residue. The initial reaction is an addition to form substituted biurets or ureas which are subsequently thermally decomposed. Solvents or suspension agents may be present. Examples relate to the preparation of methyl-, ethyl-, n-propyl-, alkyl-, and n-butyl isocyanates. Many other urea or amine reactants are specified, including chloro- and alkoxy substituted compounds.