Process for the production of asymmetrical thioindigo compounds

A process for the production of the compound of the formula I ##STR11## wherein two substituents R or R' are hydrogen or alkyl of 1 to 12 carbon atoms, one R or R' is hydrogen, a halogen atom or alkyl of 1 to 12 carbon atoms, and one R or R' is hydrogen, a halogen atom, alkyl, alkoxy, alkylthio, alkoxyalkyl, alkanoyloxyalkyl or alkylcarbamoyl, each containing 1 to 12 carbon atoms in the alkyl and alkoxy moieties and 2 to 13 carbon atoms in the alkanoyl moieties, or two adjacent substituents R or R' together are trimethylene or tetramethylene and the other substituents R are hydrogen, with the proviso that at least one substituent R is different from a substituent R', which process comprises reacting a compound of the formula II ##STR12## with a compound of the formula III ##STR13## in the presence of an inert organic solvent at a temperature between about 0.degree. and 120.degree. C. to form a compound of the formula IV ##STR14## in which formulae II, III and IV above X is chlorine, bromine or fluorine and R and R' are as defined for formula I;

• and cyclising said compound of the formula IV either directly by splitting off water, optionally in the presence of a condensation agent, with or without the addition of an inert organic solvent at a temperature between about 100.degree. and 300.degree. C., or by heating, with or without the addition of a high-boiling organic solvent, at a temperature between about 100.degree. and 300.degree. C., to give a compound of the formula I, or converting said compound of the formula IV into the corresponding acid chloride by treating it with a chlorinating agent, optionally in the presence of an inert organic solvent, at a temperature between about 0.degree. and 100.degree. C., and cyclising this latter, in the presence of a Friedel-Crafts catalyst in an inert organic solvent or in a melt at a temperature between about 0.degree. and 130.degree. C., to give a compound of the formula I.