Process for the preparation of concentrated stable liquid dye solutions of CI Direct Yellow 11 utilizing an extended surface silica filter aid during a desalting procedure

DETAILED DESCRIPTION As mentioned, the preferred starting materials are derived from the tetrasodium complex of Direct Yellow 11.
However any complex that yields the free acid complex on acidification may be desalted and stabilized by this process including the lithium Paper Yellow 11 complex according to the aforementioned U.
S.
Pat.
No.
3,905,949 (duPont).
The preferred strong inorganic acid for preparing the free acid complex is sulfuric acid.
At elevated temperatures only stoichiometric amounts are needed to complete the metathetical reaction.
Hydrochloric acid requires an excess to complete the reaction and the resulting NaCl does not vary sufficiently in solubility with temperature to permit speedy washing from the filter.
Nitric acid has been found to shift the dyestuff color slightly to longer wave lengths introducing orange shades to the dyed paper.
The alkanolamines are particularly excellent solubizers for the alkanolamine complexes.
The dyestuffs they provide disperse easily in the dyeing solutions and are self-leveling, penetrating easily into massed or felted fibers.
The useful alkanolamines have the formula ##STR2## where at least one of R', R" or R"' are HO(CH.
sub.
2).
sub.
n, the rest being H or CH.
sub.
3 (CH.
sub.
2).
sub.
m, where n is an integer from 1 to 6 and m is 0 to 6.
Preferred are triethanolamine (TEA) and diethanolamine (DEA).
Economically useful is the commercially available unrefined mixture containing 85% TEA and 15% DEA.
After acidification the slurry is heated to about reflux temperature (97.
degree.
C.
) for about 30 minutes to ensure completion of the reaction.
The neutralization reaction proceeds rapidly even at room temperature being hindered only by the viscosity of the alkanolamine.
To promote this reaction, the neutralization mixture is maintained at about 65.
degree.
C.
to ensure lowered viscosity of the mixture during conversion to the alkanolamine stilbeneazo(xy) complex and its filtration.
The final complex, after removal of the excess water, is adjusted to an absorbence of 24 at