Color Index Acid Red 176 is a chemical compound belonging to the azo and acid dye families. It is a chromotropic dye originally used for dyeing wool.
Synthesis Acid Red 176 is synthesized via the diazotization of 4-nitroaniline using sodium nitrite and hydrochloric acid, followed by azo coupling of the resulting diazonium salt with chromotropic acid.
Uses Acid Red 176 is used to dye wool a bluish-red shade. Mordanting with chromium salts, such as potassium dichromate, induces a distinct color transition from red to blue or black.
Acid Red 176 serves as an indicator in the complexometric titration of thorium and in the photometric determination of magnesium in natural waters.
History The synthesis of the dye was patented by Hoechst in 1890. In common with other chromotropic acid-derived dyes described in these patents, its application in wool printing is highlighted.
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