COMPLEX AROMATIC COMPOUNDS 



333 



The naphthalene sulphonic acids are crystalline hygroscopic solids. 



a-naphthol is crystalline, melts at 95 and boils at 280; it resembles 

 phenol in smell, is only slightly soluble in water, but dissolves easily in 

 alcohol and ether. It gives a violet flocculent precipitate with ferric chloride. 



/?-naphthol is a crystalline solid, melting at 138. It forms nitro deriva- 

 tives like phenol, many of which are used as dyes. 



a-naphthylamine is a colourless, crystalline solid melting at 50 and 

 boiling at 300. It has an unpleasant smell and turns red on exposure' to 

 air ; on oxidation it is converted into a-naphthaquinone. It gives a blue 

 precipitate with ferric chloride. 



/2-naphthylamine is a colourless crystalline solid, melting at 112 and 

 boiling at 294. It has no smell and gives no precipitate with ferric chloride. 



It gives phthalic acid on oxidation. 



a-nitronaphthalene is yellow, melts at 61 and boils at 304. 



/?-nitronaphthalene, prepared by indirect methods, melts at 79. 



The chief derivatives of naphthalene are the naphthol sulphonic acids and 

 naphthylamine sulphonic acids of which 14 isomers of each are possible. 



Naphthalene and its substitution products are extensively used in the 

 preparation of dyes. Apparently no natural compound contains a naphtha- 

 lene ring. 



Anthracene. 



a y a The chief interest attaching to anthracene 



is that it is the parent hydrocarbon from which 

 the red dye of madder root is derived. 



Anthracene is a constituent of coal tar and 

 is isolated like naphthalene from the* fraction 

 boiling above 270. 

 Its constitution has been arrived at by its resemblance in properties to 

 benzene and naphthalene and by its synthesis by treating tetrabromo-ethane 

 with benzene in presence of aluminium chloride : 



BrCHBr / CH \ 



C* TJT 1 i C* TT TJTTD /"** TT / I N/~* TT 



^6 n 6 *" T ^66 ==s 4"-^^ "T" ^6 4V I /^6^4* 



BrCHBr \CH/ 



It is a colourless crystalline solid with a blue fluorescence, melting at 

 213 and boiling at 351. It is insoluble in water, very slightly soluble in 

 alcohol and ether, but easily soluble in benzene. 



Anthracene resembles benzene and naphthalene fairly closely, but it is 

 oxidised by nitric acid and converted into anthraquinone. 



Anthraquinone. 



Anthraquinone is prepared by oxidising anthra- 

 cene with sodium bichromate and sulphuric acid 

 and is the chief derivative of anthracene. 



It consists of pale yellow needles which melt at 

 2 85. It resembles the aromatic ketones, e.g. benzo- 

 phenone, rather than quinone and is a very stable 

 compound. It is used in making alizarin and other dyes. 



Alizarin. 



Alizarin occurs in madder root as the 

 glucoside termed ruberythric acid. This 

 glucoside on hydrolysis by enzymes, or by 

 acids, gives two molecules of glucose and 

 alizarin, the " Turkey red " dye. Since its 



synthesis by Graebe and Liebermann who determined its constitution, 



alizarin is made entirely from anthraquinone, 



CO 



