ABSTRACT
In commercially available dyes the extent of conjugation typically increases in the sequence dis-, tris- and polyazo; all have more extensive aromatic systems and usually more extended conjugation than analogous monoazo dyes. Benzidine and various of its carcinogenic derivatives are intermediates in the manufacture of many dis- and polyazo dyes. For the safety of workers in the dyestuffs industry these compounds should be synthesized, diazotized and coupled entirely within enclosed apparatus. The dye was introduced as a fat stain for animal tissues, applied from aqueous alcoholic solutions, at the beginning of the 20th century by both Michaelis and Herxheimer. Sudan black B is a superlipophilic disazo dye, carrying secondary amine substituents which only ionize under acid conditions, not in routine staining solutions. The dye can be used as a substrate for demonstration of myeloperoxidase-containing leukocyte granules. The dye was proposed as a substitute for acid fuchsine in the Van Gieson procedure by Curtis as long ago as 1905.
