Patent ID: 7138522

Claim:
A process for the preparation of a rylenetetracarboxylic monoimide monoanhydride of formula IIIa or IIIb where the variables have the following meanings: R is hydrogen; C 1 –C 30 -alkyl, whose carbon chain may be interrupted by one or more —O—, —S—, —NR 2 —, —CO— and/or —SO 2 — groups and which may be monosubstituted or polysubstituted by carboxyl, sulfo, hydroxyl, cyano, C 1 –C 6 -alkoxy and/or by a 5- to 7-membered heterocyclic radical which is bonded via a nitrogen atom, may contain further heteroatoms and may be aromatic; aryl or hetaryl, each of which may be monosubstituted or polysubstituted by C 1 –C 18 -alkyl, C 1 –C 6 -alkoxy, halogen, hydroxyl, cyano, carboxyl, —CONHR 3 , —NHCOR 3 and/or aryl- or hetarylazo, each of which may be substituted by C 1 –C 10 -alkyl, C 1 –C 6 -alkoxy, halogen, hydroxyl, cyano and/or carboxyl; R 2 is hydrogen or C 1 –C 6 -alkyl; R 3 is hydrogen; C 1 –C 18 -alkyl; aryl or hetaryl, each of which may be substituted by C 1 –C 8 -alkyl, C 1 –C 6 -alkoxy, halogen, hydroxyl or cyano, which comprises monohydrolyzing an asymmetrical rylenetetracarboxylic diimide of the formula IIa or IIb where R 4 is C 5 –C 8 -cycloalkyl, whose carbon skeleton may be interrupted by one or more —O—, —S— and/or —NR 2 — groups and which may be monosubstituted or polysubstituted by C 1 –C 6 -alkyl, under alkaline conditions in the presence of a polar organic solvent.