Process for the preparation of polyisocyanates of the diphenylmethane series having reduced colour

摘要

A method (M1) for the production of polyamines of the diphenylmethane series (I) involves: (a) reaction of aniline and formaldehyde in presence of an acid catalyst to form polyamines; and (b) neutralization of the reaction mixture with base, followed by phase separation and treatment of the organic phase with a base. An Independent claim is also included for a method (M2) for the production of polyisocyanates of the diphenylmethane series (II) by carrying out method M1 as above and then reacting the polyamines obtained with phosgene.