Violanthrone, Indanthren Dark
Blue BOA,is generated by
potash fusion of benzanthrone , .
Direct potash fusion leads to side products, such
as isoviolanthrone and 4-hydroxybenzanthrone.
The crude product may be used directly or in
mixtures with other dyes in vat dyeing. It is also
used to generate violanthrone derivatives. Several
processes have been developed to decrease
the amounts of undesirable side products of the
direct potash fusion of benzanthrone or to purify
the bibenzanthronyl or the crude violanthrone
. Especially effective is the addition
of high-boiling solvents such as naphthalene, the
so-called low carbazole anthracene residues, or
sodium acetate to the melt. The quality of the
products prepared by these methods is satisfactory
for the production of almost all violanthrone
dyes.
Violanthrone of high purity is obtained
from 4,4'-bibenzanthronyl (153) by alkaline or
acid ring closure, preferably in the presence
of oxidizing agents , . If this ring
closure is carried out in sulfuric acid with
an excess of manganese dioxide, the 16,17-
violanthronequinone (155) is obtained. This can
be reduced readily with sodium hydrogen sulfite
to 16,17-dihydroxyviolanthrone (156). Subsequent
alkylation of the hydroxy groups yields
very fast navy-blue to brilliant-green vat dyes.
The dimethyl ether (157) is the well-known
dye Caledon Jade Green or Indanthren Brilliant
Green B and FFB (extremely pure form).
