Phenyl glycine ortho-carboxylic acid

Phenyl Glycine ortho-Carboxylic Acid.—The next step toward indigo is the formation of phenyl glycine ortho-carbo3grlic acid which is an ortho-dimino derivative of a mixed ring-carboxy and side-chain-carboxy acid. With chlor acetic acid anthranilic acid forms an amino acetic acid derivative in which anthranilic acid, acting as ammonia or an amine, is substituted in acetic acid. 

This compound may be termed anthranilo acetic acid, but as it is also a phenyl substituted glycine or amino acetic acid it is termed phenyl glycine ortho-carboxylic acid. The rest of the synthesis of indigo will be discussed under indigo itself, but as it all involves the original synthesis of anthranilic acid from a cheap raw material and as the phenyl glycine or//fo-carboxylic acid is an amino aromatic acid, this much has been given here. 

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. 

Naphthalene to Anthranilic Acid.—Such a cheap source was found in naphthalene which was converted into anthranilic acid, orthoamino benzoic acid, and this by treatment with chlor acetic acid yields phenyl glycine ortho-carboxylic acid. The complete synthesis is as follows Naphthalene is oxidized to or// o-phthalic acid which then yields phthalic anhydride. This with ammonia, as ammonium carbonate, yields phthalimide or phthalamidic acid. 

The anthranilic acid may also be converted into phenyl glycine ortho-carboxylic acid by the action of formaldehyde and potassium cyanide, yielding first cyano-methyl anthranilic acid which on hydrolysis is converted into the phenyl glycine compound. 

Finally the phenyl glycine ortho-carboxylic acid is fused with sodium hydroxide and converted into indoxyl which by atmospheric oxidation... 

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See also in sourсe #XX -- [ , , ]

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