| 摘要 |
1,265,853. Recovery of aromatic diisocyanates. E. I. DU PONT DE NEMOURS & CO. 12 Nov., 1969 [16 Dec., 1968], No. 55425/69. Heading C2C. A process for recovering aromatic diisocyanate values from distillation residues obtained in the phosgenation of aromatic amines comprises (1) at least partially hydrolysing the isocyanates, biurets and carbodiimides of the residues dissolved in an inert organic solvent, e.g. orthodichlorobenzene, by hydrochloric or hydrobromic acid, preferably concentrated, (2) phosgenating the resulting mixture at 125-210‹ C. in the presence of less than 10 weight per cent of water, based on the weight of still residues and (3) recovering aromatic diisocyanates from the phosgenated mixture, e.g. by vacuum distillation. The process is suitable for metaphenyl diisocyanate, 4,4<SP>1</SP>-diisocyanate diphenyl methane, xylene diisocyanate and tolylene diisocyanate. |
