Benzofuran derivatives, process for preparing them and their use as optical brighteners

摘要

Condensation of a benzofuran, which is substituted in 2-position by a carboxylic acid hydrazide group bound to the benzofuran nucleus via a bridgemember being in conjugation with the double bonds of the benzofuran, with a benzofuran-2-carboxylic acid halide yields a bisacyl hydrazide which is capable of oxdiazol ring closure while splitting off water. The so-obtained oxdiazoles are optical brighteners, especially for polyester materials.