14 января, 2016 
Pokraskin Determination of azo dyes is done most satisfactorily in the presence of sodium tartrate which prevents the precipitation of the difficultly soluble dye acids (e. g., benzopurpurin, see Knecht,105 pages 31-32). Yellow dyes cannot be easily titrated because titanium tartrate is strongly yellow in color.
The reduction takes place quantitatively according to the equation: R—N=N—R’ + 4 TiCls + 4 HC1 -» 4 TiCl4 + R—NH2 + R’—NH2
It is only necessary to know the molecular weight of the dye and the number of azo groups present. The titration is carried out exactly as described above.
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