Patent ID: 8569500

Claim:
A process for preparing a rylenetetracarboxylic dianhydride, or a salt thereof having formula Ib wherein R is phenoxy, phenylthio, pyridyloxy, pyrimidyloxy, pyridylthio or pyrimidyl-thio, each of which may optionally be mono- or polysubstituted by C 1 -C 12 -alkyl, C 1 -C 12 -alkoxy and/or aryl; m is 1 or 2; n is 4 when m=1; 4 or 6 when m=2, the process comprising a) subjecting a rylenetetracarboximide of general formula II wherein R, m and n are as defined above and R′ is hydrogen or a C 1 -C 30 -alkyl whose carbon chain may, optionally, be interrupted by one or more —O— and/or —CO— moieties and which may, optionally, be mono- or polysubstituted by: C 1 -C 6 -alkoxy, cyano and/or aryl which may, optionally, be mono- or polysubstituted by C 1 -C 18 -alkyl or C 1 -C 6 -alkoxy; or phenyl, or naphthyl, or pyridyl, or pyrimidyl, each of which may be, optionally, mono or polysubstituted by: C 1 -C 18 -alkyl, C 1 -C 6 -alkoxy, halogen, cyano, nitro, —CONR 2 R 3 , —SO 2 NR 2 R 3 , or phenyl or naphthylazo, each of which may be, optionally, mono- or polysubstituted by C 1 -C 10 -alkyl, C 1 -C 6 -alkoxy and/or cyano; or C 5 -C 8 -cycloalkyl which, optionally, may be mono- or polysubstituted by C 1 -C 6 -alkyl, where R 2 and R 3 are each independently hydrogen; C 1 -C 18 -alkyl whose carbon chain may be interrupted by one or more —O—, —S—, —CO—, —SO— and/or —SO 2 — moieties and which may be mono- or polysubstituted by C 1 -C 12 -alkoxy, C 1 -C 6 -alkylthio, hydroxyl, mercapto, halogen, cyano, nitro and/or —COOR 1 ; aryl or hetaryl to each of which may be fused further saturated or unsaturated 5- to 7-membered rings whose carbon skeleton may be interrupted by one or more —O—, —S—, —CO— and/or —SO 2 — moieties, where the entire ring system may be mono- or polysubstituted by C 1 -C 12 -alkyl and/or the above radicals specified as substituents for alkyl; and R 1 is hydrogen or C 1 -C 18 -alkyl, where the R 1 radicals may be the same or different when they occur more than once; to a hydrolysis under alkaline conditions in the presence of a polar organic solvent and removing the rylenetetracarboxylic dianhydride Ib from any rylenetetracarboxylic monoimide monoanhydride of formula Ia which is formed where R′, R, n and m have the same meanings as above, to form the rylenetetracarboxylic dianhydride, or the salt thereof having formula Ib or b) hydrolyzing the rylenetetracarboximide of general formula II under conditions that form the compound of formula Ib and substantially no rylenetetracarboxylic monoimide monoanhydride of the formula Ia.