Bayer Aktiengesellschaft

Georg Nicklas

Joachim Priemer

Nikolaus Schulz

A process has now been found for the isolation of purified anthraquinone from the crude anthraquinone which has been obtained by oxidation of naphthalene to give naphthoquinone, reaction of the oxidation product with butadiene to give tetrahydroanthraquinone, oxydehydrogenation of this reaction product with molecular oxygen to give a crude anthraquinone and optionally removal of naphthalene, phthalic anhydride and low-boiling substances from this crude anthraquinone, which is characterized in that the crude anthraquinone is treated with an oxygen compound of the elements of the first and/or second main group of the periodic system at an elevated temperature, optionally in the presence of a solvent, and purified anthraquinone is then isolated by subliming the anthraquinone present at a temperature of about 190.degree. to about 290.degree. C. and a pressure of about 1 to about 90 mm Hg and then desubliming it under the same pressure, or by vaporizing the pretreated anthraquinone at a temperature of about 290.degree. to about 380.degree. C. and a pressure of about 90 to about 760 mm Hg and condensing the vapor under a pressure of about 90 to about 760 mm Hg.

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Cologne, Germany

Georg Nicklas