GB430914A - Improvements in or relating to the manufacture of compounds of the benzanthrone series - Google Patents

Abstract

The proportion of by-products formed in the oxidation of benzanthrone for the ultimate production of Bz-2 : Bz-2<1>-dihydroxydibenzanthrone and of vat dyestuffs obtained therefrom, is reduced by carrying out the oxidation with managanese dioxide and somewhat diluted, e.g. 80 per cent sulphuric acid, and/or by a restriction of the time of reaction so that only a portion, e.g. 60 to 70 per cent of the benzanthrone is oxidized to Bz-1 : Bz-1<1>-dibenzanthronyl. The reaction product is subjected to reduction with bisulphite and extraction with alkali to remove by-products, and may then be either further extracted with organic solvents or with 75--80 per cent sulphuric acid to remove unchanged benzanthrone, or the mixture of Bz-1 : Bz-1<1>-dibenzanthronyl and unchanged benzanthrone may be fused with caustic alkali and subsequently oxidized with sulphuric acid and manganese dioxide for the production of Bz-2 : Bz-2<1>-dihydroxydibenzanthrone. In examples: (1) purified benzanthrone is dissolved in 80 per cent sulphuric acid and cooled to 2 DEG C., pyrolusite added during 7 to 8 hours, and the mixture stirred for 15 to 20 hours, the temperature being maintained throughout at 2 to 4 DEG C. A small quantity of water is then added and the product washed on a porous plate with 75 to 80 per cent sulphuric acid, whereby unchanged benzanthrone and any oxybenzanthrone are removed. The product is finally boiled with bisulphite to remove residual manganese. (2) The reaction mixture of example 1 is diluted with large excess of water, the product boiled with bisulphite, filtered, washed with caustic soda, and finally washed with warm toluene to remove unchanged benzanthrone. (3) Stronger acid (94 per cent) is used for the oxidation, but the reaction time is limited to 4 hours. The reaction product is treated with bisulphite and alkali, but the unchanged benzanthrone is not removed, approximately 35 per cent being present together with 65 per cent Bz-1 : Bz-1<1>-dibenzanthronyl. (4) The process of example 2 if stopped short of the final toluene extraction yields a yellowish brown powder containing approximately 70 per cent of substantially pure Bz-1 : Bz-1<1>-dibenzanthronyl and 30 per cent unchanged benzanthrone. (5), (6) The products of examples 3 or 4 are fused at 130 DEG C. with a melt of methanol, fused potassium acetate, and caustic potash, drowned in cold water, and aerated until the dyestuff is completely precipitated. The product is oxidized with manganese dioxide and 93 per cent sulphuric acid at 20--25 DEG C., and after filtering and treatment with bisulphite consists of Bz-2 : Bz-2<1>-dihydroxydibenzanthrone of great technical purity. (7) Pure Bz-1 : Bz-1<1>-dibenzanthronyl obtained according to example 1 is oxidized as in example 6. Specifications 251,313, 275,927, 278,112, [all in Class 2 (iii)], and 418,202 are referred to.