Sodium alizarin sulphonate

The yield of radioactive D.F.P. from 32P is necessarily small on the semi-micro scale (p. 75) it is better therefore to titrate the fluoride (obtained after the decomposition of D.F.P.) with thorium nitrate, sodium alizarin sulphonate being used as indicator.2 It is necessary, however, first of all, to remove the fluoride by distillation (p. 211). This method gives an accuracy of +1 per cent with 50 mg. of D.F.P. This degree of accuracy on a semi-micro scale3 may be considered fairly satisfactory. 

Prepare the zirconium-alizarin red S paper as follows. Soak dry filter paper in a 5 per cent solution of zirconium nitrate in 5 per cent hydrochloric acid and, after draining, place it in a 2 per cent aqueous solution of sodium alizarin sulphonate (BDH Alizarin Red S ). The paper is coloured red-violet by the zirconium lake. Wash the paper until the wash water is nearly colourless and then dry in the air. 

Mix together on a spot plate 2 drops each (equal volumes) of a 0-1 per cent aqueous solution of alizarin-S (sodium alizarin sulphonate) and zirconyl chloride solution (0-1 g solid zirconyl chloride dissolved in 20 ml concentrated hydrochloric acid and diluted to 100 ml with water) upon the addition of a drop or two of the fluoride solution the zirconium lake is decolourized to a clear yellow solution. 

The reagent consists of a 2 per cent aqueous solution of alizarin-S (sodium alizarin sulphonate). 

Alizarin. Dissolve successively in 75 ml. of water 6 g. of potassium chlorate, 20 g. of sodium anthraquinone- p-sulphonate and 75 g. of sodium hydroxide. Transfer the mixture to a 500 ml. autoclave (compare Section VI,4) and heat for 20 hours at 170°. After coohng, scrape out... 

Upon heating anthraquinone with fuming sulphuric acid at 160° for about 1 hour, the main product Is anthraquinone-p-sulphonic acid, which is isolated as the sparingly soluble sodium salt. The latter when heated imder pressure with sodium hydroxide solution and an oxidising agent (sodium or potassium chlorate) yields first the corresponding hydroxy compound further hydroxy-lation occurs in the a-position through oxidation by the chlorate and 1 2-di-hydroxyanthraquinone (alizarin) is formed. 

A mixture of 2 g. of potassium chlorate, 30 g. of commercial sodium hydroxide, 10 g. of finely powdered sodium /3-anthraquinone-sulphonate ( silver salt ), and 40 c.c. of water is heated for twenty hours at 170° (oil bath) in an autoclave or in an iron tube with screwed-on cap. The cooled melt is repeatedly extracted with hot water and the extracts, after being combined and filtered, are acidified while hot with excess of hydrochloric acid, which precipitates the alizarin. When the mixture has cooled the precipitate is collected at the pump, washed successively with dilute hydrochloric acid and water, and dried. 

Reaction LXX. Oxidation of certain Hydrocarbons. (B., 14, 1944 A. Spl., 1869, 300 E.P., 1948 (1869).)—This reaction is confined in the aliphatic series almost exclusively to the replacement by hydroxyl of the hydrogen attached to tertiary carbon atoms. A powerful oxidising agent, e.g., chromic acid in glacial acetic acid, is necessary. In the aromatic series the reaction is somewhat more easy to accomplish when the sodium salt of anthraquinone-jS-monosulphonic acid, for example, is fused under pressure with caustic soda and a little potassium chlorate, replacement of both a hydrogen atom and the sulphonic acid group by hydroxyl occurs, and alizarin ( /f-dihydroxyanthraquinone) is obtained. 

Besides these, use is also made (especially for dyeing wool), under the name of alizarin red, of the sodium salts of the respective sulphonic derivatives, which form orange-yellow powders... 

Occasionally in the synthesis of phenols by this route oxidation products are formed. A particular example is provided by the alkali fusion of sodium anthraquinone-2-sulphonate during which a second hydroxyl group is introduced into the 1-position, forming the dyestuff alizarin (1) (cognate preparation in Expt 6.99). In the procedure described the oxidation step is promoted by the deliberate introduction of potassium chlorate as an oxidant. 

Cognate preparation. Alizarin. Dissolve successively in 75 ml of water 6g (0.049 mol) of potassium chlorate, 20 g (0.065 mol) of sodium anthraquinone-2-sulphonate (Expt 6.39) and 75 g of sodium hydroxide. Transfer the mixture to a 500-ml autoclave (compare Section 2.17.2, p. 97) and heat for 20 hours at 170°C. After cooling, scrape out the violet-coloured mass and extract it three or four times with 100 ml portions of boiling water. Acidify the filtered extract with hydrochloric acid. When cold, filter the orange precipitate of alizarin at the pump, wash it thoroughly with cold water and dry at 100 °C. The yield of alizarin is 14 g (90%). It may be purified by recrystallisation... 

In this synthesis it is interesting that it is the mono-sulphonic acid of anthraquinone and not the di-sulphonic acid which is the intermediate product. Other syntheses have been used commercially. Anthraquinone may be converted into alizarin without sulphonation by treating it with a mixture of sodium hydroxide, potassium hydroxide and sodium chlorate and heating to 200°. Also electrolytically by passing a current through a mixture of anthraquinone and fused potassium hydroxide. 

They synthesized the substance from dibromoanthraquinone, but the method did not prove commercially successful. In 1869 Perkin took out a patent covering the preparation of Alizarin by sulphonating anthra-quinone and fusing the product with sodium hydroxide the yield was subsequently improved by the addition of an oxidizing agent such as sodium chlorate or potassium nitrate during the fusion with alkali. Another mordant dye associated with Alizarin which was found in madder was 1 2 4 trihydroxyanthraquinone, known as Purpurin, (4). 

Alizarin, the dyestuff contained in madder, is made from anthracene, another coal tar product, by the action of "sodium bichromate and sulphuric acid to form antbraquinone this is traniSformed by the action of sulphuric acid into anthraquinone sulphonic acid, the sodium salt of which when fused with soda and a little potassium chlorate yields a compound of alizarin containing sodium, from which alizarin itself is made by the action of acid. 

Okabayashi et al.[29] rep)orted on a dual preconcentration column system for the determination of low concentrations of fluoride using a fluoride electrode. 1 ml of sample was sorbed selectively on an anion-exchanger loaded with alizarin fluorine blue sulphonate-lanthanum complex. The columns were loaded alternately, and successively eluted with IM sodium chloride - O.S M sodium chloride. A detection limit of 1 /xg r was achieved at a sampling frequency of 24 h ... 

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