Process for the preparation of polyamines of the diphenylmethane series at a low degree of protonation
View Patent ↗The invention provides a process for the preparation of polyamines of the diphenylmethane series. This process comprises a) reacting aniline and formaldehyde in a molar ratio of 1.5:1 to 6:1, in the presence of an acid catalyst at temperatures of 20° C. to 100° C., in which the water content in the acid reaction mixture is <20 wt. % and a degree of protonation of <15% is established, and b) increasing the temperature of the reaction to a temperature of 110° C. to 250° C. when the ratio of the weight contents of p-aminobenzylaniline to 4,4′-MDA in the reaction mixture falls below a value of 1.00.
1. A process for the acid-catalysed preparation of polyamines of the diphenylmethane series, comprising
a) reacting aniline and formaldehyde in a molar ratio of 1.5:1 to 6:1 at temperatures of 20° C. to 100° C., in which the water content in the acid reaction mixture is <20 wt. % and a degree of protonation of <15% is established, and
b) increasing the temperature of the reaction to 110° C. to 250° C. when the ratio of the weight contents of p-aminobenzylaniline to 4,4′-MDA in the acid reaction mixture falls below a value of 1.00.
2. The process of claim 1 , in which step a) comprises:
(1) first reacting aniline and formaldehyde in the absence of an acid catalyst to yield the aminal,
(2) adding an acid catalyst to the aminal and
(3) continuing the reaction at temperatures of 20° C. to 100° C. and at water contents of 0 to 20 wt. %.
3. The process of claim 2 , in which in step a), after (1) reacting aniline and formaldehyde to yield the aminal, at least some of the water is removed from the aminal such that a water content of 0 to 5 wt. % is established in the aminal, and before (2) adding an acid catalyst to the aminal, and (3) continuing the reaction at temperatures of 20° C. to 100° C. and at water contents of 0 to 20 wt. %.
4. The process o of claim 1 , in which a) the reaction between aniline and formaldehyde is at a temperature of 30 to 95° C.
5. The process of claim 1 , in which the degree of protonation established in step a) is 5 to 14%.
6. The process of claim 1 , in which in step b) the temperature is increased to a value of 110° C. to 180° C.
7. The process of claim 1 , in which in step b), the temperature is increased to a value of 110° C. to 160° C.
8. A process for the preparation of polyisocyanates of the diphenylmethane series, comprising (A) phosgenating polyamines of the diphenylmethane series, wherein said polyamines of the diphenylmethane series are prepared by the process of claim 1 .
9. A process for the preparation of polyurethanes, comprising reacting polyisocyanates of the diphenylmethane series with one or more polyether polyols and/or polyester polyols to yield polyurethanes, wherein said polyisocyanates of the diphenylmethane series are prepared by the process of claim 8 .