Method of producing perylenetetracarboxylic acid derivatives

A method of producing a perylenetetra-carboxylic acid derivative of the formula:

• ##SPC4##
• where X.sub.1, X.sub.2 and X.sub.3, X.sub.4 represents the group, ##EQU1## wherein R is selected from the group consisting of hydrogen, lower alkyl, cycloalkyl of ring size 4 to 8 carbons, phenyl, phenyl substituted with one or two of the groups chloro or methoxy, and pyridyl;
• or one X of the pair X.sub.1, X.sub.2 and one X of the pair X.sub.3, X.sub.4 represent the group --C=O, the other X then being in the benzimidazole or perinone cycle, the method comprising the steps of subjecting to cyclization a dinaphthyl compound of the formula:
• ##SPC5##
• wherein X.sub.1, X.sub.2 and X.sub.3, X.sub.4 represent the group ##EQU2## wherein R is selected from the group consisting of hydrogen, lower alkyl, cycloalkyl of ring size 4 to 8 carbons, phenyl, phenyl substituted with one or two of the groups chloro or methoxy, and pyridyl;
• or one X of the pair X.sub.1, X.sub.2 and one X of the pair X.sub.3, X.sub.4 represent the group --C=0, the other X then being in the benzimidazole or perinone cycle, said dinaphthyl compound being either symmetrical or non-symmetrical with respect to the 1, 1' bond, by treating said dinaphthyl compound with a reducing agent selected from the group consisting of hydrosulphite, Rongalite and other reducing agents capable of reducing vat dyes to leuco compounds in an aqueous alkaline medium, followed by oxidation with an oxidant selected from the group consisting of atmospheric oxygen, solutions of hydrogen peroxide, Na.sub.2 Cr.sub.2 O.sub.7 or K.sub.2 Cr.sub.2 O.sub.7, and other oxidants capable of oxidizing the leuco compounds of vat dyes to the corresponding vat dyes.