Process for the preparation of carbodiimides

Claim 1

A process for the preparation of carbodiimide of the formula I R--N═C═N--R.sup.1 (I) in which R and R 1 independently of one another are C 1 -C 20 alkyl, C 2 -C 18 alkenyl, or C 2 -C 18 alkynyl; C 3 -C 10 cycloalkyl, C 3 -C 10 cycloalkenyl, heterocyclyl which has 3 to 10 ring atoms and is bonded via a C atom, heterocycloalkenyl which has 3 to 10 and is bonded via a C atom, a polycyclic hydrocarbon radical with 6 to 10 atoms, C 6 -C 14 aryl, C 7 -C 20 aralkyl, heteroaryl with 5 or 6 ring atoms or heteroaralkyl with 5 to 6 ring atoms and 1 to 6 C atoms in the alkyl group, which cyclic groups are unsubstituted or substituted by C 1 -C 12 alkyl, C 1 -C 12 alkoxy, C 1 -C 12 alkylthio, C 3 -C 6 cycloalkyl, C 3 -C 6 cycloalkoxy C 3 -C 6 cycloalkylthio, C 6 -C 10 aryl, C 6 -C 10 aryloxy, C 6 -C 10 arylthio, C 7 -C 16 aralkyl, C 7 -C 16 aralkoxy, C 7 -C 16 aralkylthio, heteroaryl with 5 or 6 ring atoms, heteroaryloxy with 5 or 6 ring atoms, cyano, halogen, C 2 -C 24 secondary amino, --C(O)OR 2 , --O(O)CR 4 , --NR 2 (O)CR 4 or --C(O)NR 2 R 3 ; R 2 and R 4 independently from each other are C 1 -C 12 alkyl, phenyl or benzyl; R 3 is hydrogen C 1 -C 12 alkyl, phenyl or benzyl; it being possible for the substituents C 1 -C 12 alkyl, C 1 -C 12 alkoxy and C 1 -C 12 alkylthio in turn to be substituted by C 1 -C 12 alkoxy, halogen, cyano, C 2 -C 24 secondary amino, --C(O)OR 2 , --O(O)CR 4 , --NR 2 (O)CR 4 , --C(O)NR 2 R 3 , cycloalkyl or heterocycloalkyl with 4-8 ring C atoms or 5 or 6 ring atoms, and for the substituents cycloalkyl, cycloalkoxy, cycloalkylthio, aryl, aryloxy, arylthio, aralkyl, aralkoxy, aralkylthio, heteroaryl or heteroeryloxy to be substituted by C 1 -C 12 alkyl, -alkoxy or -alkylthio, halogen, cyano, C 2 -C 24 secondary amino, --C(O)OR 2 , --O(O)CR 4 , --NR 2 (O)CR 4 , --C(O)NR 2 R 3 , and it being possible for cycloalkyl, cycloalkenyl, heterocycloalkyl or heterocycloalkenyl as defined for R and R 1 to be fused with C 6 -C 14 aryl or heteroaryl with 5 or 6 ring atoms, by photooxidation of a thiourea of the formula II ##STR24## in which R and R 1 are as defined above with oxygen in a solvent, which comprises carrying out the reaction in the presence of an acid trapping agent which is soluble in the reaction medium.