Stilbene dyes of importance are mostly direct yellow dyes for cellulosic fibers, especially paper. There have been several red and blue stilbene‐containing dyes reported but none have been developed to commercial importance. There are brown leather dyes which are stilbene‐based. Most stilbene dyes are derived from 4‐nitrotoluene‐2‐sulfonic acid which is oxidized under alkaline conditions to 4,4′‐dinitro‐2,2′‐stilbenedisulfonic acid, which can be further condensed to yellow dyes or reduced to 4,4′‐diamino‐2,2′‐stilbenedisulfonic acid. The latter can be tetrazotized and coupled to yield dyes of reasonably definitive structure. 4,4′‐Diamino‐2,2′‐stilbenedisulfonic acid is more important as an intermediate for fluorescent brighteners than for dyes. Dyes produced by alkaline condensation of 4‐nitrotoluene‐2‐sulfonic acid or 4,4′‐dinitro‐2,2′‐stilbenedisulfonic acid are listed as a subclass of azo dyes. Those dyes derived from coupling the tetrazo of 4,4′‐diamino‐2,2′‐stilbenedisulfonic acid are listed as regular azo dyes. Since 1980 activity has been reported in all known areas of stilbene dye chemistry, but it is minuscule compared to other dye chemistries. There were reports of using 4,4′‐diaminostilbene‐2,2′‐disulfonic acid as a bridging group in reactive dyes and one report of stilbene participating in the chromophore. Basic dyes reported were made by coupling the tetrazo of 4,4′‐diaminostilbene and quaternizing. The most important stilbene dyes are those known for more than fifty years. The commercial importance of Direct Yellow 11 (1883), Direct Orange 15 (1888), Direct Yellow 4 (1886), and Direct Yellow 106 (1936) attests to the value, properties, and durability of stilbene yellow dyes.
Azine, oxazine, and thiazine dyes were among the earliest of synthetic dyes. The names are derived from the 6‐member heterocyclic ring system present in all dyes of these classes: 1,4‐diazine, 1,4‐oxazine, and 1,4‐thiazine. Azine, oxazine, and thiazine dyes were historically more important than they are at present. However, at least one example of each, introduced more than 100 years ago, is still offered commercially today. Azo and anthraquinone dyes have largely displaced them in commercial application. Azo dyes offer better fastness and broader shade ranges at more economical prices. Azine dyes are used extensively as biological stains. Colors are mostly yellow to red. Oxazine dyes have seen use as laser dyes and titration indicators. Oxazine dyes containing sulfonic acid groups are claimed to be suitable for dyeing leather in brown shades. Methylene Blue CI Basic Blue 9(CI 52015), is the classic thiazine dye still in use today. Thiazine is not important in dyes as such, but it is a part of some reactive dyes.
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