Patent GB-738650-A (GB)
Title: Process for the reduction of nitroanthraquinones
IPC: C09B1/22
Filed: 1952-01-10
Abstract: The invention comprises 1-amino-anthraquinones containing as the only other substituent an alkyl sulphone, alkyl mercapto or thiol group in either the 6- or 7-position of the anthraquinone nucleus, the alkyl groups containing at most 5 carbon atoms.  The compounds are prepared by reduction of 1-nitro-6- or 7-alkylsulphone-anthraquinones with a water-soluble salt of hydrosulphuric acid, when at 100 DEG  C. the products are 1-amino-6- or 7-mercapto-anthraquinones, whilst at lower temperatures the 6-alkyl sulphone group is not reduced.  The mercapto groups may then be alkylated with an alkylating agent containing at most 5 carbon atoms, and thereafter oxidized to the corresponding sulphones with e.g. hydrogen peroxide.  Detailed examples are given and the preparation of the starting materials is described (see Group IV (b)).  Specification 689,279 is referred to.ALSO:The invention comprises 1-amino-anthraquinones containing as the only other substituent an alkyl sulphone, alkyl mercapto or thiol group in either the 6- or 7-position of the anthraquinone nucleus, the alkyl groups containing at most 5 carbon atoms. These compounds are prepared from 1-nitro-6- or 7-alkyl-sulphone-anthraquinones by reduction with water-soluble salts of hydrosulphuric acid, when at elevated temperatures the products are 1-amino-6-or 7-mercapto anthraquinones.  At low temperatures the reduction is incomplete in the case of the 1-nitro-6-alkyl sulphone, yielding a 1-amino-6-alkyl sulphone, which can thus be separated from the product obtained on reduction of an isomeric mixture of nitrated b -alkyl sulphone anthraquinones, and then subsequently reduced to 1-amino-6-mercapto-anthraquinone.  Alkylation of the mercapto derivatives with alkylating agents providing at most 5 carbon atoms gives the corresponding alkyl mercapto compounds, which may be oxidized, particularly with hydrogen peroxide, to alkyl sulphones. In examples: (1) 2-methylsulphone-anthraquinone is nitrated, and the mixture obtained reduced with sodium hydrosulphide at 64 DEG  C., when 1-amino-6-methylsulphone-anthraquinone separates from the cooled solution.  Treatment of the filtrate with sodium chloride precipitates the sodium salt of 1-amino-7-mercapto-anthraquinone, which is methylated with methyl iodide to 1-amino-7-methylmercapto-anthraquinone and finally oxidized with hydrogen peroxide to give 1-amino-7-methylsulphone-anthraquinone; (2) 1-nitro-6-methylsulphone-anthraquinone is reduced as in (1) to 1-amino-6-methylsulphone-anthraquinone; (3) as in (2), carrying out the reduction at 100 DEG  C. to give 1-amino-6-mercapto-anthraquinone, which is then treated with methyl iodide, yielding 1-amino-6-methyl-mercaptoanthraquinone; (4) 1-nitro-7-methylsulphone-anthraquinone is reduced as in (1) to 1-amino-7-mercaptoanthraquinone, which is methylated to 1 - amino - 7 - methyl - mercapto - anthraquinone; (5) 2-isopropyl-sulphone-anthraquinone is nitrated and the product reduced with sodium hydrosulphide to yield 1-amino-6-isopropyl-sulphone-anthraquinone.  Specification 689,279 is referred to.  The preparation of the starting materials 1-nitro-6-methylsulphone- and 1-nitro-7-methylsulphone - anthraquinone by nitration of 2 - methylsulphone-anthraquinone is described in detail.