Background The xanthenes 1 are among the oldest synthetic dyes. Fluorescein was prepared originally in 1871 by Baeye# by the condensation of resorcinol with phthalic anhydride catalyzed by zinc chloride. Eosin, tetrabromofluorescein, was synthesized by Fischer and was the subject of subsequent controversy between Baeyer and H~ ffmann.~ x&x//0 o/ONa
