| 摘要 |
The invention relates to a process for the preparation of concentrated storage-stable aqueous solutions of yellow azo- and azoxystilbene dyes which are obtained by self-condensation of 4-nitrotoluene-2-sulfonic acid in the presence of an alkali metal hydroxide, by converting the sparingly soluble alkali metal salt of the dye into a water-soluble ammonium salt by double cation exchange via a lipophilic ammonium salt, which process comprises carrying out the double ion exchange in a two-phase system of nitrobenzene/water and using, for the first ion exchange a di- or trialkylamine containing a total of 12 to 40 carbon atoms and, for the second ion exchange, a mono-, di- or trialkanolamine containing 2 to 4 carbon atoms in each alkyl moiety. The concentrated storage-stable dye solutions so obtained are particularly suitable for dyeing paper.
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