Alizarin dyes alkali

We know now that dyeing is an adsorption phenomenon but no one has met specifically the two points raised by Witt. The answer has recently been given implicitly in a paper by Weiser and Porter, who showed that alumina takes up alizarin in the form of the ahzarin anion, because one gets the same red lake whether the lake is treated with acid or alkali, whereas solid sodium alizarate is purple and solid alizarinic acid is yellow. 

Pure -nitroabzarin forms orange-yellow needles, which melt at 244°, with partial decomposition [19]. It sublimes in yellow leaflets, undergoing partial decomposition. It dissolves in benzene and glacial acetic acid, and gives a purple-red solution with alkalies. The violet lime-lake is not decomposed by carbonic acid. (Distinction from alizarin.) It forms a diacetyl compound, M.P. 218° [19]. Nitroalizarin dyes orange shades on alumina mordants, and reddish-violet on iron mordants. 

Quinizarin dissolves, like oxyanthraquinones, in alkalies with a violet colouration. (Try it.) Since it does not contain the hydroxyl groups in the vicinal a-/3-positions, it will not form dyes with metallic-salt mordants. This will be explained further under Alizarin. 

Of the numerous di- and poly-oxyanthraquinones only those are actual dyes which contain, like alizarin, two hydroxyl groups in the vicinal a-/J-i>osition, i.e. the derivatives of alizarin (Rule of Liebermann and Kostanecki). The above prepared quinizarin dissolves in alkalies with a violet colouration, but with metallic oxides it forms no salts on fibres. 

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 is reduced to anthracene when heated with zinc-dust—a transformation which was the first step taken in determining the structure of the dye contained in madder-root. The view that alizarin is a dihydroxyl derivative of anthraquinone, follows from the fact that it is formed as the result of the fusion of anthraquinone-sulphonic acid with caustic alkalies, and from the synthesis of the dye by heating phthalic anhydride and pyro-catechol with sulphuric acid at 150° —... 

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