Bayer Aktiengesellschaft

Nikolaus Schulz

Heinz U Blank

Karlheinrich Meisel

Friedrich-Wilhelm Ullrich

Willi Streicher

Joachim Priemer

Gunther Klag

Dieter Irmscher

Georg Nicklas

Indoles of the formula ##STR1## can be prepared by reaction of a phenylhydrazine of the formula ##STR2## which is unsubstituted in at least one ortho-position, with a ketone of the formula ##STR3## in an aqueous medium in the presence of an acid compound, less than 5 equivalents, based on 1 mol of phenylhydrazine, of an acid compound having a pK value of 1.3-4.5 being employed.

Process for the preparation of indoles

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.

Process for the isolation of purified anthraquinone

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Kuerten, Germany

Nikolaus Schulz