US Patent 7807836 Preparation of perylen-3,4:9,10-tetracarboxylic dianhydride and also of naphtalene-1,8-dicarboximides

A process for preparing perylene-3,4:9,10-tetracarboxylic dianhydride, comprising: dimerizing a naphthalene-1,8-dicarboximide of the formula IIa;