Process for the preparation of isocyanates by decomposition of N,N,N'-trisubstituted ureas

摘要

Process for the preparation of isocyanates, which is characterised in that N,N,N'-trisubstituted ureas of the formula in which R1, R2 and R3 are identical or different and denote a straight-chain, branched or cyclic (C1-C24) alkyl radical which is unsubstituted or substituted by (C1-C6) alkoxy, optionally substituted phenyl, halogen or by other radicals which are inert under the reaction conditions used, or R2 and R3 together denote a heterocyclic non-aromatic ring which can optionally also contain further heteroatoms, are decomposed at elevated temperature in a diluent which is inert under the reaction conditions to a readily volatile isocyanate of the formula R1NCO and a poorly volatile secondary amine of the formula R2R3NH whose boiling point lies above the boiling point of the isocyanate and above the reaction temperature used, after which the isocyanate is stripped off at the top by means of a carrier gas stream.