Process for preparing dyes of the dibenzopyrenequinone series

摘要

The production of vat dyes of the dibenzopyrenequinone type is conventionally based on 1,5-dibenzoylnaphthalene. To prepare this starting material for the oxidative ring closure, naphthalene is dibenzoylated in aluminium chloride using a benzoyl chloride excess of 70%. When the naphthalene derivative produced is isolated, this excess benzoyl chloride has to be inconveniently washed out in the form of benzoic acid. In addition, for the subsequent cyclisation, the resulting dibenzoyl compound, which still contains many by-products, must first be brought to the required purity (>/=de 95%) by reprecipitation from organic solvent. The invention now provides a one-pot process starting from naphthalene. In this process, the dibenzoylation of the naphthalene is carried out with an excess of only 5% of benzoyl chloride, and the melt of 1,5-dibenzoylnaphthalene is then - without intermediate isolation thereof - subjected to the oxidative ring closure reaction, bromination and finally work-up to the desired dye.