Abstract: Naphthoquinone having a purity of higher than 95% is separated from an aqueous slurry of naphthoquinone and phthalic acid prepared by contacting, with an aqueous medium, a reaction mixture gas containing naphthoquinone and phthalic anhydride formed by a catalytic vapor phase oxidation of naphthalene. An extraction of naphthoquinone is carried out with a chain or cyclic saturated hydrocarbon at 60.degree. to 110.degree. C. under the condition adjusting pH to 1.2 to 5 and substantially dissolving phthalic acid in the aqueous phase and leaving resinous materials as a bottom.

Abstract: A process for oxidizing an organic compound by ceric sulfate dissolved in an aqueous sulfuric acid solution, wherein the organic compound is oxidized (1) by means of a ceric sulfate-aqueous sulfuric acid solution or a cerous sulfate-containing ceric sulfate-aqueous sulfuric acid solution in which the molar concentration (mol/liter) of ceric sulfate is at least the molar concentration of cerium (ions) contained in the molecules of cerous sulfate at the maximum solubility of cerous sulfate in an aqueous sulfuric acid solution at the final sulfuric acid concentration (exclusive of ceric sulfate and cerous sulfate) and at the temperature under the oxidation reaction conditions and at most the saturated molar concentration of ceric sulfate in said aqueous sulfuric acid solution, (2) under a condition such that at the end of the oxidation reaction, the concentration of ceric sulfate is maintained at a level capable of dissolving cerous sulfate which is present at a concentration of at least the maximum solubility o

Abstract: A process for preparing a quinone, which comprises reacting a polynuclear aromatic hydrocarbon and a ceric salt in an aqueous acid solution in the presence of an organic solvent selected from the group consisting of chlorobenzene and an alkylbenzene represented by the general formula: ##STR1## where each of R.sub.1, R.sub.2 and R.sub.3 is an alkyl group and the total carbon number of the alkyl groups is from 3 to 6.

Abstract: A method for electrolyzing cerous sulfate in the electrolytic oxidation of cerous sulfate to ceric sulfate in an aqueous sulfuric acid solution, characterized in that the concentration of the cerous sulfate in the electrolyte to be supplied to the electrolytic cell is maintained, by the presence of ceric sulfate, at a level of at least the saturated concentration of cerous sulfate in the aqueous sulfuric acid solution (exclusive of the cerous sulfate and ceric sulfate) at the initial sulfuric acid concentration and at the temperature of electrolysis, and at most the saturated concentration of cerous sulfate in the presence of the ceric sulfate in the aqueous sulfuric acid solution at the initial sulfuric acid concentration and at the temperature of electrolysis, and the concentration of the ceric sulfate in the electrolyte is maintained at a level of at most the saturated concentration of ceric sulfate in the aqueous sulfuric acid solution at the initial sulfuric acid concentration and at the temperature of e

Abstract: In a process for purifying crude anthraquinone obtained by the oxidation, by molecular oxygen in an aqueous alkali metal hydroxide solution, of an adduct obtained by the Diels-Alder reaction of butadiene with 1,4-naphthoquinone obtained by a catalytic vapor phase oxidation reaction of naphthalene, an improvement characterized in that said crude anthraquinone is subjected to oxidation treatment in an aqueous medium in the presence of a hypochlorite.

Abstract: 1,4,4a,9a-Tetrahydroanthraquinone compounds are produced by Diels-Alder reaction of 1,4-naphthoquinone with a conjugated diolefin in the 1,4,4a,9a-tetrahydroanthraquinone compound as a reaction medium.

Abstract: A hydroanthraquinone is produced from a reaction mixture obtained by the Diels-Alder reaction of naphthoquinone with a conjugated diolefin in an inert organic solvent. The reaction mixture in an inert organic solvent is oxidized with an oxidizing agent to decompose quinhydrone or quinhydrone derivative produced by said Diels-Alder reaction and the crystallized hydroanthraquinones are separated from said inert organic solvent.

Abstract: In a process for separation of naphthoquinone and phthalic acid from an aqueous slurry prepared by contacting a reaction mixture gas formed by a catalytic vapor phase oxidation of naphthalene with an aqueous medium, the decomposition of naphthoquinone is prevented and phthalic acid is substantially separated by adding a base to the aqueous slurry so as to neutralize only sulfuric acid component and maleic acid component without substantially neutralizing phthalic acid component and heating the aqueous slurry to dissolve phthalic acid to form a slurry of naphthoquinone in an aqueous solution of phthalic acid and extracting naphthoquinone with a solvent while preventing a crystallization of phthalic acid.A pH of the aqueous slurry is adjusted in a range of 1.2 to 2.5 before the heat dissolution of phthalic acid and the extraction of naphthoquinone.