Anthraquinone-1-sulfonic acid,
K salt, also called diamant salt, is
prepared by sulfonation in the presence of, e.g.,
0.5 % mercury in 20 % oleum, an amount of
SO3 adequate for the sulfonation of about 60 %
of the charge. The reaction is controlled in such
a manner that about 50 % of the anthraquinone
remains unsulfonated. After mercury is precipitated
as the sulfide, the unreacted anthraquinone
is precipitated by dilution and is collected by
filtration. After washing and drying, it is recirculated
as ‘reclaimed quinone‘. Mercury is
removed completely from the filtrate, and the
anthraquinone-1-sulfonic acid is then precipitated
as the potassium salt .
