Reducing discoloration in crude di:phenyl-methane di:isocyanate prodn.

摘要

In the prodn. of mixts. (crude MDI) (I) of diphenylmethane diisocyanates and polyphenyl-polymethylene polyisocyanates by reacting corresp. mixts. of diphenylmethane diamines and polyphenyl-polymethylene polyamines with COCl2 in the presence of inert organic solvent(s) (II) at elevated temp., the I2 colour no. is reduced by adding phenols (III) after phosgenation and before sepg. excess COCl2 and (II) and heat treatment of the reaction prod.Pref. (III) may be mono- or polyhydric and pref. polycyclic. They are added in amts. of 0.001-10 (wt.%) w.r.t. (I) in the reaction mixt., pref. when the mixt. contains 0.01-3% COCl2.