Process for the isomerization of aromatic amines

A process for the isomerization of 2,4′-methylenedianiline and/or 2,2′-methylenedianiline to 4,4′-methylenedianiline, respectively, the process comprising

• (1) preparing a feed F2 comprising 2,4′-methylenedianiline and/or 2,2′-methylenedianiline and optionally further comprising aniline;
• (2) providing a catalyst C2 comprising a Bronsted acid;
• (3) contacting the feed F2 prepared in (1) with the catalyst C2 provided in (2), obtaining a mixture M2 comprising 4,4′-methylenedianiline as a reaction product;
• (4) optionally separating the 4,4′-methylenedianiline from the reaction product obtained in (3);
• wherein the feed F2 in (1) comprises 5 wt.-% or less of formaldehyde.

A process for the isomerization of 2,2′-methylenedianiline to 2,4′-methylenedianiline, the process comprising

• (1′) preparing a feed F3 comprising 2,2′-methylenedianiline and optionally further comprising aniline;
• (2′) providing a catalyst C3 comprising a Bronsted acid;
• (3′) contacting the feed F3 prepared in (1′) with the catalyst C3 provided in (2′), obtaining a mixture M3 comprising 2,4′-methylenedianiline as a reaction product;
• wherein the feed F3 in (1′) comprises 5 wt.-% or less of formaldehyde.