Process for the production of polyisocyanates

Details Process for the production of polyisocyanates Process for the production of polyisocyanates

C - Chemistry, Metallurgy

07

C

260/456.1

C07C 265/14 (2006.01)

Patent

CA 1239414

PROCESS FOR THE PRODUCTION OF POLYISOCYANATES ABSTRACT OF THE DISCLOSURE The present invention is directed to a process for the preparation of polyisocyanates of the diphenyl- methane series having a high diamine content and a low 2,2' diamino-diphenylmethane content by condensing aniline with formaldehyde in the presence of hydro- chloric acid as catalyst, neutralizing the acid catalyst at the end of the condensation reaction and working up the polyamine mixture thus obtained by distillation, characterized in that a) in a first reaction stage, from 2.0 to 3.5 moles of aniline are reacted with 1 mole of formaldehyde in the presence of hydrochloric acid or a condensation product produced from 2.0 to 3.5 moles of aniline and 1 mole of formaldehyde in the absence of acid catalyst is reacted in the presence of hydrochloric acid at a degree of protonation maintained at 40 to 60% at temperatures below 50°C, b) more aniline is then added to the reaction mixture so that the molar ratio of amine nitrogen atoms in the form of free aniline and the reaction products formed in accordance with a) to formaldehyde chemically bound in the form of methylene bridges in those reaction products rises to more than 10:1 and up to 20:1 with the degree of protonation decreasing correspondingly, c) the reaction mixture obtained in accordance with b) is heated to allow the N-substituted intermediate products present to be completely rearranged into polyamines containing unsubstituted primary amino groups, d) the reaction mixture obtained in accordance with c) is worked up by distillation after neutralization of the acid and phosgenating the resultant polyamides.

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