Indigo, manufacture

Finally, it is appropriate to close this chapter with an example from the roots of fine chemicals the dyestuff, indigo. Manufacture of indigo involves chemistry (see Fig. 2.15) which has hardly changed from the time of the first commercial synthesis more than a hundred years ago (see earlier). Mitsui Toatsu has developed a two-step process in which indole is produced by vapour-phase reaction of ethylene glycol with aniline over a supported silver catalyst (Inoue et al., 1994). Subsequent liquid-phase oxidation of the indole, with an alkyl hydroperoxide in the presence of a soluble molybdenum catalyst, affords indigo. 

Reppe was also working on the preparation of ethylene oxide. The first step was the reaction of ethylene with chlorine and water to form ethylene chlorohydrin (2-chloroethanol). He was able to convert the unsatisfactory batch process, which had been used for indigo manufacture, into a continuous process. This was called the tower process (Turm-Verfahren), because a mixture of ethylene and a carefully controlled amount of chlorine was driven up a tower filled with water. The dilute solution of ethylene chlorohydrin was drawn off at the top and then heated, without being isolated, with lime water to form ethylene oxide. Ethylene oxide was chiefly converted into the glycol by adding water, but it could also be used to make diethylene glycoF (diglycol). 

Figure 2.82 Indigo manufacture from anthranilic acid...

Jewett, J. E. Treating molten materials with liquids as in indigo manufacture. U.S. Patent 1934716, 1933 Chem. Abstr. 1934, 28, 7236. 

P. Reed, The early years of the indigo manufacture in Britain , I.G. Farhen Study Group Newsletter, (1989), 10-17, p. 13. 

Many sodium compounds are made from sodium. Sodium is employed as a reducing agent in numerous preparations, including the manufacture of dyes (see Dyes and dye intermediates), eg, indigo herbicides (qv) (128) pharmaceuticals (qv) high molecular weight alcohols (129) perfume materials (130) (see Perfumes) and isosebacic acid (131,132). 

Piesendy, all ceitified colois aie factory-piepaied materials belonging to one of several different chemical classes. Although a few such as D C Blue No. 6 (indigo) are known to exist in nature, certified colors owe their commercial importance to their synthetic production. Because of the starting materials used in their manufacture in the past, certified colors were once known as coal-tar dyes. Today, since most of the raw materials used in their preparation are obtained from petroleum, this term no longer appHes. 

V-Phenyl glycine [103-01 -5] the key intermediate for indigo, may be manufactured by alkylation of aniline with chloroacetic acid, but it is much more economical, even though three in situ stages are required, to use formaldehyde as the alkylating agent. 

This serendipitous discovery marked the beginning of the synthetic dyestuffs industry, based on coal tar as its main raw material, which is, incidentally, a waste product from another industry, steel manufacture. The development of mauveine was followed by efficient syntheses of natural dyes such as alizarin in 1869 (Graebe and Liebermann, 1869), and indigo in 1878 (Bayer, 1878 Heumann, 1890). The synthetic production of these dyes marked the demise of the agricultural production of these materials and the advent of a science-based, predominantly German chemical industry. The present-day fine chemicals and specialties, e.g. pharmaceuticals, industries developed largely as spin-offs of this coal tar-based dyestuffs industry. 

Herz A process for making o-amino thiophenols by heating the hydrochlorides of aromatic amines with sulfur monochloride at 50 to 75°C. The products are used as intermediates in the manufacture of thio-indigo dyestuffs. Invented by R. Hertz in Germany in 1914. 

Indolebutyric acid org chem C12H13O2N A crystalline acid similar to indoleacetic acid in auxin activity. Abbreviated IBA. in,dol-byu tir-ik as-od indoxyl orgchem (C8H6N)0H A yellow crystalline glycoside, used as an intermediate in the manufacture of indigo. in dak-sol ... 

N-phenylglycine org chem C8H5NHCH2COOH A crystalline compound, moderately soluble in water, melting at 127-128°C used in dye manufacture (indigo). en fen-arglT,sen )... 

Uses Manufacturing phthalates, phthaleins, benzoic acid, synthetic indigo, pharmaceuticals, insecticides, chlorinated products, and artificial resins. 

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