| abstract |
Stilbene azo dyes, as lithium salts or mixed lithium and sodium salts wherein the ratio of lithium to sodium is at least 1:2, especially useful for dyeing paper or paper pulp, prepared by condensing a member of the group consisting of the lithium salt of 5-nitro-o-toluenesulfonic acid and the dilithium, monolithium monosodium, and disodium salts of 4,4''-dinitro-2,2''stilbenedisulfonic acid, in an aqueous alkaline medium, at a temperature of from about 20*C. to the boiling temperature of the reaction medium, in the presence of sufficient ionic lithium to provide a ratio of lithium to sodium in the dye of at least 1:2 until formation of said stilbene azo dye is substantially complete, the condensation reaction product optionally being reacted with a reducing agent selected from the group consisting of aliphatic aldehydes, hydroxyaliphatic aldehydes, glycerol, alkanolamines, alkali metal sulfites and alkali metal sulfides to achieve shade variation. |