Process for the preparation of organic isocyanates, in particular mixtures of diphenylmethane diisocyanates and polymethylene polyphenylene polyisocyanates, with reduced colour number

摘要

The invention relates to a process for the preparation of organic isocyanates, in particular crude MDI, with reduced colour number by phosgenation of the corresponding amines and polyamines in the presence of at least one inert solvent at elevated temperature, subsequent separation of the excess phosgene and solvent and thermal treatment of the reaction products, at least one inorganic acid chloride and at least one antioxidant being present according to the invention after phosgenation is complete during the further working-up and thermal treatment before or after the separation of the excess phosgene.