Anthraquinone derivatives of the formula IMAGE where at most two of R originate from the group comprising H, CH3, C2H5 and C3H7, but at least two of R originate from the group comprising the substituents OH, CH2OH, C2H4OH, the esters of these substituents with carboxylic acids having at most 3 C atoms or the glycosides of these substituents, where a plant containing the anthraquinone derivative or an extract of this plant is extracted by means of a solvent - in particular at elevated temperature - are prepared by the following process: a) the plant or extract is extracted by means of a first hydrophilic solvent, in particular by means of water, an alcohol having a maximum of 3 C atoms, acetone, ethyl acetate, diethyl acetate [sic], or mixtures of these solvents and the extract is then filtered; b) the resulting solution is either evaporated - preferably to a residual content of at least 5, in particular to 10 to 15 per cent by weight of solvent to a syrupy consistency - or passed through a polar ion exchanger, for example Amberlite IR45, from which the retained anthraquinone derivatives are eluted using methanol; c) the compound is extracted from the syrup by means of a second solvent, in particular benzene and/or a homologue thereof, which step is preferably repeated 2 to 4 times with the residue from the extraction; d) the extract is evaporated to dryness and optionally recrystallised. The filtrate resulting after step a) can be exposed to air and light for several days - in particular several times successively - before step b), preferably with stirring and/or introduction of oxygen and/or with UV irradiation.
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