Process for the preparation of pigments of the anthanthrone series
AssigneeHoechst Aktiengesellschaft
InventorsErnst Spietschka, Manfred Urban
Life of this patent
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Abstract
Process for the preparation of pigments of the anthanthrone series of the formula ##STR1## in which R.sub.1 and R.sub.2 denote chlorine, bromine or iodine atoms or C.sub.1 -C.sub.4 -alkoxy groups, having valuable properties, which comprises first converting the anthanthrones of the formula mentioned, in the form of the crude pigment, in an aqueous alkaline medium and at a pH>10, into the leucoform, precipitating the latter by adding inorganic or organic acids, reoxidizing the aqueous suspension of the leuco-form to give the anthanthrones and subjecting the resulting finely divided pre-pigments of the formula mentioned to a solvent finish.
Claims5
A process for the preparation of a pigment of the anthanthrone series having the formula ##STR3## in which R.sub.1 and R.sub.2 denote chlorine, bromine or iodine atoms or C.sub.1 -C.sub.4 -alkoxy groups, which comprises:
- a. reducing with sodium dithionite a crude anthanthrone of the said formula to the leuco form in an alkaline medium at a pH>10,
- b. adding an inorganic or organic acid, to pH 7 to 11.5, to precipitate the leuco anthanthrone,
- c. oxidizing the resulting aqueous suspension of leuco anthanthrone at a pH of 7 to 11.5 to give finely-divided anthanthrone pre-pigment, and
- d. treating the resulting finely divided anthanthrone pre-pigment with solvent.
Dependencies are inferred from the claim text.