Process for the preparation of benzimidazolylbenzofuranes

摘要

Optical brighteners of the formula <IMAGE> wherein the radicals R1 to R9 are substituents customary in brightener chemistry, A(-) denotes a colorless anion, w denotes the valency of the anion A and n denotes 0 or 1, are obtained in a simple manner when a compound of the formula <IMAGE> is heated to 110 DEG -200 DEG C. in an inert solvent, without the addition of a catalyst.