Patent ID: 8853443

Claim:
A process for preparing an isocyanate, comprising (i) hydrogenating a first mixture (Gi) comprising an amine and at least one precursor to a coloring substance in the presence of a hydrogenation catalyst comprising copper to obtain a second mixture (Gii) comprising the amine and a smaller amount of said at least one precursor to a coloring substance than in said first mixture (Gi); (ii) reacting the second mixture (Gii) with phosgene to obtain a third mixture (Giii) comprising the isocyanate, wherein said amine is at least one amine selected from the group consisting of a polyamine and a diamine, wherein said diamine is at least one selected from the group consisting of phenyldiamine, tolyldiamine, naphthylenediamine, diphenylmethanediamine and wherein said polyamine is at least one polycyclic or higher molecular weight derivative of a diamine selected from the group consisting of phenyldiamine, tolyldiamine, naphthylenediamine, diphenylmethanediamine and a mixture thereof.