GB443972A - Improvements in or relating to the manufacture of a pigment colour from n-dihydro-1:2:2:1-anthraquinone azine - Google Patents

Abstract

Anthraquinone vat dyes; dye preparations; lakes.--Pigments are obtained by oxidation of a crystalline leuco salt of N-dihydro-1 : 2 : 2<1> : 1<1>-anthraquinoneazine, preferably in the form of an aqueous suspension, with a nitrobenzenesulphonate or a nitrotoluenesulphonate. The covering power of the products is greater than that of the products obtained by air oxidation of the solid leuco salt, by oxidation of the dissolved leuco compound with sodium m-nitrobenzenesulphonate or by precipitation of the azine from sulphuric acid, and the shade is a redder tint of blue. The products are specially suitable for colouring paper and may be used in admixture with the greener product obtainable by precipitation from sulphuric acid to obtain the desired shade. The precipitation of the colour is preferably effected in the presence of an alkali in amount insufficient to dissolve the leuco crystals. The following examples are specified. (1) b -Aminoanthraquinone is fused with a mixture of sodium and potassium hydroxides at about 205 DEG C., the fusion mass is drowned in water and the solid leuco salt of the N-dihydro-1 : 2 : 2<1> : 1<1>-anthraquinoneazine A isomer is separated and suspended in water at 20--35 DEG C., sodium hydrosulphite is added followed by a slurry of sodium m-nitrobenzenesulphonate in water, the mixture is stirred until the oxidation is complete, and the pigment is isolated by filtration and washed free of alkali &c. (2) N-Dihydro-1 : 2 : 2<1> : 1<1>-anthraquinoneazine, as sold commercially under the name Ponsol blue R is vatted with caustic soda and sodium hydrosulphite, the leuco crystals are salted out, filtered off, washed with weak caustic soda solution containing some sodium hydrosulphite, suspended in water at 20--35 DEG C. with addition of more hydrosulphite while stirring, followed by a slurry of sodium m-nitrobenzenesulphonate in water, the stirring is continued until the oxidation is complete and the product is isolated as in (1). (3) The sodium m-nitrobenzenesulphonate in (2) is replaced by sodium p-nitrotoluene-o-sulphonate. In all cases the pigment may be formed in presence of a salting out agent, e.g. sodium chloride or aluminium sulphate, a wetting agent, e.g. an abietene sulphonate or an alkylated naphthalene sulphonate, a dispersing agent, e.g. cellulose sulphite waste liquor or an alkali metal caseinate, a protective colloid, e.g. glue, or a substratum, e.g. alumina, barytes, silica, clay, talc, asbestos, magnesium carbonate, lithopone, titanium oxide and zinc oxide, and an agent, e.g. an aluminium hydroxide floc adapted to bind the pigment to the substratum may be present. Other specified oxidizing agents are the sodium and potassium salts 1-methyl-2-nitrobenzene-4- and 6-sulphonic acids. The Specification as open to inspection under Sect. 91 comprises also the oxidation of a crystalline leuco salt of any vat dyestuff of the anthraquinone series with any oxidizing agent acting more rapidly than air. Other specified dyestuffs are the monochloro-, monobromo-, 3 : 3<1> - dichloro- and 3 : 3<1> - dibromo - derivatives of N-dihydro-1 : 2 : 2<1> : 1<1> - anthraquinoneazine, flavanthrone, pyranthrone and halogenated pyranthrones and other specified oxidizing agents are sodium peroxide, the sodium and potassium salts of 1-methyl-2-nitrobenzene-4-and 6-carboxylic acids, or of 1-methyl-2-nitro-4-and 6 - oxybenzenes, nitrobenzoic acids and nitrophenols and soluble oxidizing salts of the naphthalene and anthracene series. This subject-matter does not appear in the Specification as accepted.