Abstract:
A number of 2-chlorobenzophenones, containing
electron releasing groups (e.g. hydroxy, thiomethoxy and
methoxy) in the 4' - position, were prepared by the Friess
rearrangement, or the Friedel-Crafts reaction. These
ketones, when treated with potassamide in liquid ammonia,
underwent partial Haller-Bauer scission, unlike 2-chlorobenzophenone
which is known to undergo complete scission.
Under similar conditions 4-nitrobenzophenone
also underwent partial scission, but the main reaction in
this case was nucleophilic amination of the nitro containing
ring. This amination reaction was shown not to be a useful
general reaction for aromatic nitro compounds.
3-Methylxanthone was then prepared by treatment
of 2- and 3- chloro-2'-hydroxy-5'-methylbenzophenone with
. little, if any, attendant scission. The corresponding 2fluoro-
compound also gave the xanthone, but as the 3-fluoro
compound did not, it was concluded that the 2-fluoro compound
reacted through a nucleophilic substitution mechanism, rather
than the benzyne mechanism invoked for the chloro and bromo
compounds.
3-Methylthioxanthone was synthesised by treatment
of methyl 4-tolyl sulphide and 2-chlorobenzoyl chloride
with aluminum chloride in carbon disu1phide, followed.by heating.
This compound was also prepared by treatment of 3-chloro-2'thiomethoxy-
5'-methylbenzophenone with potassamide in liquid
ammonia.
