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.