Bayer Aktiengesellschaft

Gunter Hammen

Hartmut Knofel

Michael Brockelt

Herbert Stutz

Stefan Penninger

Klaus Konig

Stefan Wershofen

Theodor Engbert

Rudolf Sundermann

Thomas Schieb

Wolfgang Friederichs

Klaus Jost

Process for the preparation of isocyanates

The present invention relates to an improved process for the production of monomeric and polymeric poly(O-alkylurethanes) of the diphenyl methane series. The process comprises the reaction of the corresponding amines with dialkyl carbonates in the presence of a catalyst, followed by the isolation of the products in a highly pure form. The invention also relates to the use of the produced monomeric and polymeric poly(O-alkylurethanes) for the production of the corresponding isocyanates.

Process for the production of poly(O-alkylurethanes) of the diphenyl

The present invention relates to a process for the preparation of a polyisocyanate comprising

Process for the preparation of polyisocyanates

N-monosubstituted carbamic acid esters are thermally split on a continuous basis in a tube reactor. The carbamic acid ester which is flowed down or passed over the inner wall of a tube reactor is thermally split at a temperature of from 150.degree. to 450.degree. C. and under a pressure of from 0.001 to 20 bar into at least two fractions. One fraction is predominantly isocyanate and a second fraction is predominantly hydroxyl compound. These fractions may be separated by removing one as a gaseous fraction formed under the splitting conditions from the head of the reactor and collecting the second fraction as a liquid which accumulates at the base of the reactor. If both fractions are gaseous under the splitting conditions, they are both removed from the head of the reactor and subsequently separated by fractionating columns for example. This process is particularly advantageous in that isocyanate and hydroxyl fractions are obtained in high yield without using a solvent.

Continuous process for thermal splitting of carbamic acid esters

Cycloaliphatic triisocyanates or isomer mixtures of such triisocyanates corresponding to the formula ##STR1## in which R represents hydrogen or a C.sub.1 -C.sub.4 alkyl group are produced by phosgenating the corresponding cycloaliphatic triamines or isomer mixtures of such triamines or a salt thereof. These triisocyanates are useful in the production of polyisocyanate addition products, particularly polyurethane coatings and lacquers.

Cycloaliphatic triisocyanates

Triisocyanates and isomeric mixtures of triisocyanates corresponding to the formula ##STR1## in which R represents hydrogen or an alkyl group having from 1 to 4 carbon atoms are made by phosgenating the corresponding triamine. These triisocyanates are particularly useful in the production of polyurethanes, especially polyurethane lacquer coats.

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Rommerskirchen, Germany

Gunter Hammen