Process for the preparation of polyisocyanates of the diphenylmethane group having a reduced color value

摘要

The invention relates to a process for the preparation of polyamines of the diphenylmethane series, comprising a) reacting aniline and formaldehyde in the presence of an acid catalyst to form polyamines, and b) neutralizing the reaction mixture formed in a) with a base, wherein at least one alcohol is present during and/or after the neutralization step. The molar ratio of the alcohol to the formaldehyde is at least 0.02:1. In addition, the present invention relates to a process for the preparation of polyisocyanates of the diphenylmethane series, according to the process as described above, additionally comprising: c) phosgenating the resultant polyamines into the corresponding polyisocyanates of the diphenylmethane series.