Dyestuffs/synthetic dyes

As early as 2500 bce m India indigo was used to dye cloth a deep blue The early Phoenicians discovered that a purple dye of great value Tyrian purple could be extracted from a Mediterranean sea snail The beauty of the color and its scarcity made purple the color of royalty The availability of dyestuffs underwent an abrupt change m 1856 when William Henry Perkin an 18 year old student accidentally discovered a simple way to prepare a deep purple dye which he called mauveme from extracts of coal tar This led to a search for other synthetic dyes and forged a permanent link between industry and chemical research... 

Sulfonic Acid-Based Dyestuffs. Sulfonic acid-derived dyes are utilized industrially in the areas of textiles (qv), paper, cosmetics (qv), foods, detergents, soaps, leather, and inks, both as reactive and disperse dyes. Of the principal classes of dyes, sulfonic acid derivatives find utiUty in the areas of acid, azoic, direct, disperse, and fiber-reactive dyes. In 1994, 120,930 t of synthetic dyes were manufactured in the United States, of which 5,600 t were acidic (74). The three largest manufacturers of sulfonic acid-based dyes for use in the United States are BASF, Bayer, and Ciba-Geigy. 

The first synthetic dyestuff, mauveine, was discovered by Perkin in 1856 in the UK and led to many investigations of the derivatives of coal tar as potential coloring matters. The first dia2onium salt derived from picramic acid was prepared in 1858 and is still the basic chemistry behind coundess commercial products. Despite these inventions, in 1900 the vast majority of dyestuffs were still of natural origin. Now at the end of the century the situation has changed dramatically synthetic dyes dominate. 

Flavones. These compounds are the most widely distributed natural coloring matter formerly used as dyestuffs. The term flavone was first suggested in 1895 (69), and is indicative of their yellow color ijlavus, Latin for yellow). They have lost their commercial value as dyes since the advent of synthetic dyes in 1856. 

The chemical nature of most organic pigments is closely similar to that of the synthetic dyes that have been discovered during the past 150 years. In fact, with the exception of the phthalocyanines, almost every chemical class of pigments has been developed first for dyestuff use. There are some signs that this may not continue to be the case, with the development of some new organic pigments for specialised uses. 

Toxicology of Certain Azo Dyes. It has been known for over 100 years that certain amines used to manufacture synthetic dyes caused bladder cancer, especially 2-naphthylamine, benzidine and 4-aminodiphenyl. All the major dyestuff manufacturers abandoned the use of these amines in the production of dyes in the early 1970s. 

PERKIN, SIR WILLIAM HENRY (1838-1907). An English chemist who was the first to make a synthetic dyestuff (1856). He studied under Hofman at the Royal College of London. Perkin s first dye was called mauveine, but he proceeded to synthesize alizarin and coumarin, the first synthetic perfume. In 1907 he was awarded the first Perkin Medal, which has ever since been awarded by the American Division of the Society of Chemical Industry for distinguished work in chemistry. Not withstanding the fact that Perkin patented and manufactured mauve dye in England, the center of the synthetic dye industry shifted to Germany, where it remained until 1914. 

The success of logwood, from the heartwood of the tree Haematoxylan campechianum L found in Central America, as a black dyestuff also depended on complex formation. The active constituent of logwood is the chroman hematein (4), which is itself red. When applied with a chromium mordant, however, logwood gave black shades and held the premier position for blacks and blues until the late 1890s, by which time synthetic dyes accounted for some 90% of the dyes used. 

The development of the synthetic dye industry led to the emergence of classical organic chemistry. Its application in industry was rapid. From the end of the nineteenth century the intermediates employed in the manufacture of synthetic dyes were used to make pharmaceutical products such as aspirin. Some synthetic dyes exhibited bactericidal properties they were called medicinal dyes. Sulfonamides, drugs introduced in the 1930s, are based on research into dyestuffs and their intermediates. Less fast dyes have... 

Naturally occurring dyestuff, for example, indigo shrub, madder root, cochineal insects, Persian berries, and the like, have been known and used for centuries. These soluble dyes were rendered insoluble in water by treatment with suitable precipitating agents and used as lakes. With the increase in the variety of synthetic dyes available and multiplicity... 

Aniline Dyes.—Aniline and many of its derivatives, also many related amino derivatives of both benzene and naphthalene hydrocarbons, are of great technical importance in the manufacture of dyes. As the first synthetic dye, mauve, was made from aniline the name aniline dyes is often used synonymous with coal tar dyes for all synthetic dyestuffs, though, as we shall find, there are several groups, some of which are in no sense related to aniline. The dyestuffs and the intermediate products connected with their preparation will be referred to as we come to each compound. 

Synthetic Dyes.—Ip common usage the term aniline dye is applied to any dyestuff prepared from organic chemical substances. As the first dye made and many of those made at present are derived from aniline the above name is significant. It is not a true name, however, in many cases for though some of the azo and benzidine dyes (p. 573) may be considered as aniline derivatives those derived from naphthalene can not be so considered. Other dyes which we shall study later. 

The preceding discussion of the tri-phenyl methane and pyronine dyes is by no means exhaustive but enough has been said to give the student some idea of the importance of the dye compounds which are derived from the hydrocarbon tri-phenyl methane also to give the principal facts in connection with their relation to the history of synthetic dyes and to the question of chemical constitution and color of dyestuffs. 

Azo dyes based on the aromatic intermediate benzidine were invented in 1884. These were the first synthetic dyes that adhered to cotton fabrics without the need for a fixing agent (mordant). For this reason they were known as direct or substantive dyes. The first member was discovered by Paul Bottiger, at Bayer. From benzidine (25) and naphthionic acid (20) he obtained a red bisazo dyestuff (26)41 see Scheme 9. 

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