Abstract: The invention relates to a process for the preparation of perylene-3,4,9,10-tetracarboxylic acid N,N'-dialkyldiimides by reacting perylene-3,4,9,10-tetracarboxylic acid dianhydride with an alkylamine in aqueous suspension at a low temperature, in the course of which the bis-(alkylammonium) salt of perylene-3,4,9,10-tetracarboxylic acid bis-N-alkylamide is formed. The latter is reacted with a metal salt to give the corresponding sparingly soluble metal salt, which is subjected to the cyclization reaction at an elevated temperature. The pigments prepared by the process according to the invention are distinguished by high purity and are suitable for pigmenting lacquers and plastic compositions.

Abstract: A perylene-3,4,9,10-tetracarboxylic acid dianhydride pigment, useful as a varnish pigment, made by adding an aqueous solution of an alkali metal salt of perylene-3,4,9,10-tetracarboxylic acid and a surfactant to an acid at a pH below 3, at 0.degree. C. to 90.degree. C., and then heating the suspension so obtained at 50.degree. C. to 150.degree. C.

Abstract: The invention provides a process for the preparation of 4,7-dichloro-3-hydroxy-thionaphthene by reaction of 2,5-dichlorophenyl-thioglycolic acid chloride in dichloromethane in the presence of Friedel-Crafts catalysts.

Abstract: Very pure, transparent pigments of high color strength, of the formula ##STR1## in which R is hydrogen or alkyl having 1 to 4 C atoms, X is chlorine and/or bromine and n is a number from 0 to 4 are obtained by converting the corresponding crude pigment to the sulfate, isolating the sulfate, liberating the pure product from the sulfate by hydrolysis, separating off the pure product and dry milling the anhydrous material, with or without additives and with or without subsequent solvent finishing. These pigments are suitable for coloring paints and plastic compositions, especially for pigmenting metallic paints.

Abstract: Thioindigo and its derivatives are obtained in high yield and excellent purity by oxidizing corresponding 3-hydroxy-thionaphthenes with peroxo-disulfate in an aqueous alkaline solution.

Abstract: Coarsely crystalline crude dioxazine pigments are subjected to dry milling while maintaining their crystallinity as far as possible until the desired degree of fineness is reached and then treated with a solvent.

Abstract: Thioindigo and its derivatives are obtained in high yield and excellent purity by oxidizing corresponding 3-hydroxythionaphthenes with peroxo-disulfate in an aqueous alkaline solution.