The invention relates to a process for increasing the selectivity of the
hydrogenation of 4,4'-diaminodiphenylmethane (4,4'-MDA) to
diaminodicyclohexylmethane (4,4'-HMDA) by catalytic hydrogenation of a
mixture containing 4,4'-MDA as the main component and its mono-N-methyl
derivative as a secondary component. According to the invention, the
hydrogenation is terminated before a conversion of 4,4'-MDA to 4,4'-HMDA
of 99% is achieved. Under these conditions, a substantially smaller
proportion of the N-methyl-4,4'-MDA is hydrogenated to N-methyl-4,4-HMDA.