Process for the manufacture of indigoid dyes

Claim 1

A process for the manufacture of indigo Compounds wherein a functional derivative of the anthranilic acid of the general formula I ##STR8## in which A is unsubstituted or substituted benzene, naphthalene, anthracene, phenanthrene, fluorene, acenaphthene, pyrene, quinoline or phenothiazine, wherein the substituent is selected from the group consisting of alkylene, aliphatic, cycloaliphatic, araliphatic or aromatic hydrocarbon radicals, etherified hydroxyl groups and halogen atoms, x represents a hydrogen atom or a protective group for the free amino group which can form an anhydro derivative with the carboxyl group in the ortho-position, said protective group being the acyl radical of a substituted or unsubstituted aliphatic, cycloaliphatic, cycloaliphtic-aliphatic, aromatic, araliphatic carboxylic acid or of a carbonic acid hemiester or carbonic acid, is reacted with nitromethane in the presence of a base selected from the group consisting of alkali metal hydrides, alkali metal amides, alkali metal alcoholates of lower alkanols or alkali base or with a salt of nitroacetic acid to give the ω-nitro-o-amino-acetophenone derivative of the general formula II ##STR9## in which A and X are as defined in formula I, and this intermediate is condensed by heating with aqueous organic or inorganic acid to give the indigo compound of the general formula III ##STR10## in which A is as defined in formula I.