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C26H28014
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C26H28014 +2H20 = 2 See also:C6H,2O6 +C14H804 Ruberythric See also:acid = See also:Glucose +See also:Alizarin. Alizarin was known to the ancients, and until 1868 was obtained entirely from See also:madder See also:root. The first step in the synthetical See also:production of alizarin was the See also:discovery in 1868 of C. Graebe and C. See also:Liebermann that on See also:heating with See also:zinc dust, alizarin was converted into See also:anthracene. In See also:order to synthesize alizarin, they converted anthracene into See also:anthraquinone and then brominated the quinone. The dibrominated product so obtained was then fused with See also:caustic potash, the melt dissolved in See also:water, and on the addition of hydrochloric acid to the See also:solution, alizarin was precipitated. This See also:process, owing to its expensive nature, was not in use very See also:long, being superseded by another, discovered simultaneously by the above-named chemists and by See also:Sir W. H. See also:Perkin; the method being to sulphonate anthraquinone, and then to convert the sulphonic acid into its See also:sodium See also:salt and fuse this with caustic soda. In practice, the crude anthracene is purified by solution in the higher See also:pyridine bases, after which treatment it is frequently sublimed. It is then oxidized to anthraquinone by means of sodium dichromate and sulphuric acid in leaden vats, See also:steam heated so that the mixture can be brought to the See also:boil. When oxidation is See also:complete the crude anthraquinone is separated in See also:filter presses and heated with an excess of commercial oil of See also:vitriol to 12o° C., the various impurities See also:present in the crude material being sulphonated and rendered soluble in water, whilst the anthraquinone is unaffected; it is then washed, to remove impurities, and dried. The anthraquinone so obtained is then heated for some See also:hours at about 150-16o° C. with fuming sulphuric acid (containing about 4o-5o % SO3), and by this treatment is converted into anthraquinone-(3-monosulphonic acid. The solution is poured into water and sodium carbonate is added to neutralize the excess of acid, when the sodium salt of the monosulphonic acid (known as See also:silver salt) separates out. This is filtered, washed, and then fused with caustic soda, when the sulpho-See also:group is replaced by a hydroxyl group, and a second hydroxyl group is simultaneously formed; in order to render the formation of this second group easier, a little See also:potassium chlorate or sodium nitrate is added to the reaction mixture. The melt is dissolved in water and the dyestuff is liberated from the sodium salt by hydrochloric or sulphuric acid, or is converted into the See also:calcium salt by digestion with hot See also:milk of See also:lime, then filtered and the calcium salt decomposed by acid. The precipitated alizarin is then well washed and made into a See also:paste with water, in which See also:form it is put on to the See also:market. K. Lagodzinski (Berichte, 1895, 28, p. 1427) has synthesized alizarin by condensing hemipinic acid [(CH3O)2C6H2(COOH)2] with See also:benzene in the presence of See also:aluminium chloride. The product on acidification gives a See also:compound C15H12O5•H2O which is probably an oxy-methoxy-benzoyl benzoic acid. This is dissolved in See also:cold concentrated sulphuric acid, in which it forms a yellowish red solution, but on heating to See also:roe C. the See also:colour changes to red and See also:violet, and on pouring out upon See also:ice, the monomethyl See also:ether of alizarin is precipitated. This compound is hydrolysed by hydriodic acid and alizarin is obtained. It can also be synthesized by heating catechol with See also:phthalic anhydride and sulphuric acid at 150° C. See also:C6H4<C0>O+C6H,(OH)z[1.2] = H20+C6H4<CD>C6Hz(OH)2. Pure alizarin crystallizes in red prisms melting at 290 C. It is insoluble in water, and not very soluble in See also:alcohol. It dissolves readily in caustic alkalis on See also:account of its phenolic See also:character, and it forms a yellow-coloured di-acetate. Its value as a dyestuff depends on its See also:power of forming insoluble compounds (lakes) with metallic oxides. It has no See also:affinity for See also:vegetable See also:fibres, and consequently See also:cotton goods must be mordanted before See also:dyeing with it (see DYEING). Numerous derivatives of alizarin are known. On solution in glacial acetic acid and addition of nitric acid, (3-nitroalizarin OH See also:CON OH (alizarin See also:orange) 1 1 is produced, and this on heating. `/See also:NCO/N/NO2 with sulphuric acid and See also:glycerin is converted into alizarin See also:blue. The trioxyanthraquinones—purpurin, anthrapurpurin, anthragallol and flavopurpurin—are also very valuable dyestuffs. These compounds may be represented by the following formulae: OH OH OH ,CO OI;OH HO/\/COa/\OH /CO /\OH /CO\/\OH 0co /0 I\)NCO/L) HOV CO/0 0 CO/UGH. uH I'urpurin. Anthrapurpurin. Flavopurpurin. Anthragallol. Purpurin (1.2.4 trioxyanthraquinone) is found with alizarin in madder root; it is now prepared synthetically by oxidizing alizarin with See also:manganese dioxide and sulphuric acid. After the separation of the silver salt (see above) obtained on sulphonating anthraquinone, the remaining acid liquid gives on treatment with calcium carbonate the calcium salt of anthraquinone 2.6 disulphonic acid (anthraquinone-a-disulphonic acid). This is converted into the sodium salt by means of sodium carbonate, and on See also:alkali See also:fusion yields flavopurpurin. In a similar manner anthrapurpurin is prepared by alkali fusion of anthraquinone 2.8 disulphonic acid. Anthragallol is synthetically prepared by the condensation of benzoic and gallic acids with sulphuric acid OH OH / COOH+ i ~OH O/COQ/\OH J HOOC\/OH-2H.0 { NCO/IL/10H or from See also:pyrogallol and phthalic anhydride in the presence of sulphuric acid or zinc chloride. A. See also:Baeyer in 1890, by heating alizarin with fuming sulphuric acid for 24-48 hours at 35-40° C., obtained a product, which after treatment with caustic soda gave a sulphuric acid ester of quinalizarin, and this after acidification and boiling was converted into quinalizarin (Alizarin See also:Bordeaux) or 1.2.6.9 tetra-oxyanthraquinone. Penta-oxyanthraquinones have been obtained from purpurin and anthrapurpurin, while a hexaoxyanthraquinone has been obtained from 1.5 dinitro-anthraquinone. Additional information and CommentsThere are no comments yet for this article.
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