Process for the preparation of di(amino phenyl)methanes

Abstract

Aniline and formaldehyde are condensed (2-10 moles aniline per mole of formaldehyde) at ambient temperature in the absence of acid catalysts to give a mixture of aminals (anilinoacetals) and aniline from which the water is removed. The anhydrous aminals are contacted with a solid catalyst (clays, zeolites, diatomaceous earth) using either batch or continuous operation initially at 20.degree. C to 55.degree. C until benzylamine formation is substantially complete, then at 50.degree. C to 65.degree. C until benzylamine conversion to methylene polyphenyl polyamines is 75 - 90% complete and finally at 80.degree. C to 100.degree. C. A polyamine mixture is obtained in which diaminodiphenylmethane is the major (order of 90 percent by weight or higher) component, the bulk of the higher oligomeric polyamines being triamine. The diaminodiphenylmethane component contains of the order of 85 percent of 4,4'-isomer, the rest being 2,4'-isomer except for very small amounts (order of 2 percent or less) of 2,2'-isomer. Advantages of the process include high yield of diaminodiphenylmethane with relatively high 4,4'-isomer content, low oligomeric polyamine content, low temperature operation (energy consumption lower), no acidic reactants to cause corrosion of equipment, and rapid rates of conversion.