Nitro, acids phenyl propiolic acid

Diphenyl-diacetylene is the parent hydi ocarhon of indigo blue, and the dye itself can be prepared by means of tliis reaction, starting with o-nitro-phenyl-propiolic acid. By loss of carbon dioxide the acid becomes o-nitro-phenyl-acetylene, the copper derivative of which passes to di-ortho-nitrophenyl-diacety-lene ... 

It is necessary to prepare first, o-nitro-phenyl-propiolic acid, which is itself obtained from o-nitro-cinnamic acid. Cinnamic ester (50 gms.) is nitrated by pouring gradually into cooled nitric acid (sp. g. 1-5). 

Benzaldehyde, ortho-Nitro Cinnamic Acid, ortho-Nitro Phenyl Propiolic Acid.—Later he started with benzaldehyde and obtained first benzal chloride which by condensation with sodium acetate yielded cinnamic acid salt. 

From the cinnamic acid salt by nitration he obtained ortho-nitro cinnamic acid. This yielded a di-bromide which by loss of two molecules of hydrogen bromide was converted into ortho-nitro phenyl propiolic acid (p. 700). 

Finally ortho-nitro phenyl propiolic acid when heated with alkali and glucose, the latter acting as a reducing agent, yielded indigo. He also converted ortho-miio phenyl propiolic acid into indigo by the following series of reactions. 

The following are examples of the reduction of nitro-compounds by ferrous sulphate nitro-phenyl propiolic acid1 and nitro-dichlor-benzaldeliyde2 the method has been used to reduce several nitro-acids to the corresponding amino-acids.3... 

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