Process for preparing isocyanates.

摘要

Prodn. of isocyanates of formula (I) ROCH2NCO (R=1-4C alkyl or allyl) comprises reacting a urea of formula (II) ROCH2NHCONR'R" (R' and R" = inert organic residues or together complete a heterocycle) with a mono- or polyisocyanate (III), of b.pt. >1 that of (I), at 50-250 degrees C. Pref. reaction is carried out in presence of cpd. (IV) having carbodiimide gps.; opt. an isocyanate cotng. such gps. can serve as both (III) and (IV). (I) esp. where R=CH3, are intermediates for crosslinkable binders used in paints. The method is suitable for large scale operation and avoids using hazardous chloromethyl alkyl ethers.