Heumann indigo synthesis

By far the most important member of these vat dye families is C.I. Vat Blue 1 (indigo). Its synthesis can be achieved via the four-step method shown in Fig. 13.129. The method shown is known as the Heumann-Pfleger... 

Since Baeyer s work was more directed to the elucidation of the structure of indigo, the synthesis he had discovered could not be applied economically on a large scale. Karl Heumann, at the Federal Polytechnic in Zurich, discovered a method of synthesis which was based on phenylglycine, which can be produced from aniline and chloroacetic acid. The yield from this process, however, was still unsatisfactory. Heumann s second proposal used phenylglycine-o-carboxylic add, obtained by first oxidizing naphthalene to phthalic anhydride. 

In the synthesis due to Heumann and Pfleger the fusion yields the potassium derivative of indoxyl, which is dehydrogenated to indigo even by atmospheric oxygen at the same time hydrogen peroxide is produced (see p. 175). 

In the Heumann I synthesis, which is the basis of modem synthetic indigo production (see Section 3.5), ring closure takes place by C-C bond formation. Aniline is first treated with a chloroacetate salt to give phenylglycine salt 5, which... 

On account of the carboxyl group in the ortho position, ring closure occurs more readily than in the case of A-phenylglycine salt 11. This makes it possible to attain yields of between 70 and 90%, even without the use of sodium amide. Isolation of indigo from the suspension is carried out as in the Heumann I synthesis... 

Heumann s Synthesis, Phenyl Glycine Ortho-carboxylic Acid.—The synthesis that has resulted in placing synthetic indigo on the market is that of Heumann by the fusion of phenyl glycine ortho-carboxylic acid with caustic potash. The product of this fusion is indoxyl which by atmospheric oxygen is oxidized to indigo. The industrial success of this synthesis was achieved only when the preparation of the-phenyl glycine ortho-carboxylic acid from a cheap source was accomplished. 

Heumann-Pfleger indigo synthesis. Cycli-zation of phenylglycine to indoxyl followed by oxidation by air or oxidizing agents, such as ferric chloride, to yield indigo. 

In the industrially used Heumann-Pfleger synthesis, N-phenylglycine 1, readily accessible from aniline, is transformed through indoxyl 2 into indigo 3 in a targeted fashion (Scheme 1-1). 

Scheme 1-1 Industrial production of indigo 3 by the Heumann-Pfleger synthesis [15] from 1 via 2 to 3.

Synthesis After A. von Baeyer achieved the first synthesis of I. in 1878 and the exact structure was elucidated in 1883, further syntheses of I. were developed, the best of which was that by Heumann in 1890. Like natural 1., synthetic I. contains the isomeric indigo red, the content of the latter ranges from 2-4% in Bengal I. to 15% in Java I. The biosynthesis proceeds from indole and/or L-tryptophan and has not been completely clarified . ... 

Heumann-Pfleger synthesis (indigo) 145 Hinsberg synthesis (thiophene) 98 Hoffmann-Loffler reaction 158 Huisgen synthesis... 

For example, the indigo synthesis depended on Adolf Baeyer at Munich, after 1875, and Karl Heumann at ETH, Zurich, who discovered the basis of industrial manufacture in 1890. 

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