Syntheses of 8-Chloro and 11-Chlorobenzanthrone and their Ullmann Condensation

Abstract

An improved procedure for the syntheses of the two isomeric 8-chloro (4) and 11-chlorobenzanthrone (6) was devised and their condensation, by Ullmann reaction, to the corresponding dibenzanthronyls was achieved with the object of synthesizing violanthronyl derivatives.
The product (mp 118°C) of reduction of 1-chloroanthraquinone (2) by Sn and glacial acetic acid which had been reported to be 4-chloro-9-anthrone (5), was found, by chromatographical separation, to be mixed crystals of two isomeric (5) (mp 137°C) and 1-chloro-9-anthrone (3) (mp 118°C), whose ratio was about 2 : 1.
(5) was converted into pure (6) (mp 178°C) in 46% yield by the glycerol condensation. On the other hand, (4) (mp 182°C) obtained from (3) in this manner was the same product as the one obtained by the glycerol condensation of the reduction product of (2) in cone. H₂SO₄ with Al powder. (2) was converted into isomeric chlorobenzanthrones by a simultaneous reaction of reduction with aniline sulfate and condensation with glycerol. The product was separated by alumina chlomatography to (6) in 18% yield and (4) in 15% yield.
Ullmann reaction of (4) and (6) was carried out in naphthalene, and 95% yield of 8, 8'-dibenzanthronyl was obtained from the former, while 11, 11'-dibenzanthronyl was obtained only in 7.8% yield from the latter.