Process for the preparation of polyisocyanates

US5043471A · kind A · utility

Assignee

• BAYER HEALTHCARE LLC · DE

Inventors

• Gunter Hammen · Dormagen, DE
• Hartmut Knofel · Odenthal, DE
• Wolfgang Friederichs

Key dates

• Filing date: May 4, 1990
• Grant date: Aug 27, 1991
• Expiry date: May 4, 2010

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C07C263/04
• WIPO field: Organic fine chemistry
• WIPO sector: Chemistry

Abstract

The present invention relates to a process for the preparation of a polyisocyanate comprising PA1 (a) thermally decomposing in a tube reactor a solution of an N-substituted carbamic acid ester corresponding to said polyisocyanate in a solvent used as decompositoin medium, wherein said solvent (i) is capable of dissolving the carbamic acid ester, (ii) is stable at the decomposition temperature and chemically inert towards the carbamic acid esters and the polyisocyanate product, (iii) can be distilled without decomposing under the conditions of decomposition of carbamic acid estes, and (iv) has at least one miscibility gap with an extracting agent used according to the extraction step (c), said solutions being carried along the internal wall of reactor; PA1 (b) separating the gaseous materials formed in the tube reactor by fractional condensation into a fraction I comprised mainly of the alcohol by-product and a fraction II comprised mainly of polyisocyanates, isocyanatourethanes, unreacted carbamic acid ester, and the solvent used in step (a); PA1 (c) extracting the polyisocyanate from said fraction II with an extracting agent that is at least partly immiscible with the decompositio…