Patent ID: 7393956

Claim:
A process for preparing perylene-3,4:9,10-tetracarboxylic diimides of the general formula I wherein R is C 1 -C 30 -alkyl whose carbon chain may be interrupted by one or more —O— moieties and/or which may be substituted by one or more substituents selected from the group consisting of C 5 -C 8 -cycloalkyl (which may be substituted by one or more C 1 -C 6 -alkyl substituents), phenyl or phenyl-C 1 -C 6 -alkyl (which may each be substituted by one or more C 1 -C 18 -alkyl and/or C 1 -C 6 -alkoxy substituents), —OCOR 1 , —N(R 1 ) 2 , —SO 2 NH 2 , —SO 2 N(R 1 ) 2 , —CON(R 1 ) 2 and —COOR 1 ; C 5 -C 8 -cycloalkyl whose carbon skeleton may be interrupted by one or more moieties selected from the group consisting of —O—, —S— and —NR 2 — and/or which may be substituted by one or more C 1 -C 6 -alkyl substituents; phenyl, phenyl-C 1 -C 6 -alkyl, naphthyl or hetaryl, which may each be substituted by one or more substituents selected from the group consisting of C 1 C 18 -alkyl, C 1 -C 6 -alkoxy, phenylazo, naphthylazo, pyridylazo, pyrimidylazo, cyano, —N(R 1 ) 2 , —CON(R 1 ) 2 and —COOR 1 ; R 1 is C 1 -C 6 -alkyl, C 5 -C 8 -cycloalkyl, phenyl or phenyl-C 1 -C 6 -alkyl; R 2 is C 1 -C 6 -alkyl, phenyl or phenyl-C 1 -C 6 -alkyl, comprising: dimerizing a naphthalene-1,8-dicarboximide of the formula II in a substantially homogeneous reaction medium consisting essentially of an apolar aprotic organic solvent and an alkali metal base and subsequently reoxidizing the resulting alkali metal salt of the leuco form of the perylene-3,4:9,10-tetracarboxylic diimide in the presence of a polar solvent.