| 摘要 |
In the preparation of diisocyanates from diamines, urea and alcohols with thermal cracking of the biscarbamate formed, it has hitherto been impossible to utilise the by-products formed in the cracking stage, and thus to arrive at a technically practicable and economical process. It was therefore the object of the invention to search for an appropriate way which avoids the said disadvantages.
<??>The object was achieved when a cyclic process for the preparation of (cyclo)aliphatic diisocyanates was found wherein, starting from diamines, by-products from the thermal cracking, urea and alcohol, the biscarbamate is produced in the presence of N-unsubstituted carbamates and dialkyl carbonates and with removal of NH3, the subsequent cracking of the biscarbamate is carried out in the liquid phase without solvent, the diisocyanate and alcohol are condensed, the diisocyanate is subjected to a final distillation and a part of the reaction mixture from the cracking with the by-products formed is purged and, after first being reacted with raw alcohol arising, is recycled to the biscarbamate preparation stage.
<??>Preparation of (cyclo)aliphatic diisocyanates. |
