Chromotropic dyes are a class of azo dyes formed by reacting various diazonium salts with chromotropic acid as a coupling component. The synthesis of chromotropic dyes was patented by Farbwerke vorm. Meister, Lucius & Brüning in Höchst a. M. (later Hoechst AG) in 1890. Originally, they were used primarily to dye wool. By adding various metal salts during the dyeing process—such as copper sulfate or potassium dichromate—these dyes can produce vibrant shades ranging from red to burgundy and violet to black. Due to this diversity and versatility in color tones, the dyes were named chromotropes.
Chromotropic dyes are also used in histological staining—such as in Gömöri trichrome staining—or as indicators in complexometric titrations.
Chromotrope Name Chromotrope 2R Chromotrope 2B Chromotrope 6B Chromotrope 10B Structural formula Hue red blue-red violet-red red-violet CAS Number 4197-07-3 548-80-1 4197-09-5 5850-63-5 PubChem 20172 68360 160740 135870601 Color Index C.I. 16570 C.I. 16575 C.I. 16600 C.I. 16640 Color Index Name Acid Red 29 Acid Red 176 Acid Violet 6 Acid Violet 13 Molecular Formula C16H10N2Na2O8S2 C16H9N3Na2O10S2 C20H16N4Na2O9S2 C20H12N2Na2O8S2 Molar mass 468.37 g·mol−1 513.37 g·mol−1 566.47 g·mol−1 518.43 g·mol−1
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