| 摘要 |
A mixture of yellow azo- and azoxystilbene dyes having the shade of a C.I. Direct Yellow 11 dye is obtainable from the self-condensation of 4,4'-dinitr o- 2,2'-stilbenedisulfonic acid in the presence of an alkali metal hydroxide an d an excess of formaldehyde beyond that needed for the conversion of 4,4'dinit ro- 2,2'-stilbenedisulfonic acid to Direct Yellow 6. Concentrated aqueous solutions of the dyes are obtainable by converting the sparingly soluble alkali metal salt of the dye into a water-soluble alkanolammonium salt by a double cation exchange via a lipophilic ammonium salt, in which process the double ion exchange is carried out in a two-phase system of methyl isobutyl ketone/water and using, for the first ion exchange a trialkylamine containin g 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 dyes are especially useful for dyeing paper.
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