334 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Anthraquinone is converted by sulphonation with sulphuric acid at 

 250, or by heating with fuming sulphuric acid at 160, into anthraquinone- 

 /3-monosuiphonic acid. The solution is diluted with water, unchanged 

 anthraquinone is filtered off and the solution neutralised with soda. Sodium 

 anthraquinone-/3-monosulphonate crystallises out and is purified by crystallisa- 

 tion. It is heated with caustic soda and a small quantity of potassium 

 chl'orate ; the sodium salt of alizarin is obtained from which alizarin is pre- 

 cipitated on acidifying : 



/ CO \ / CO \ 



r\ TT / \f tr _L TJ Qn r* w ' \f tr Qn w _i_ tr c\ 



L/gii 4 \ xV^gin 4 + ri 2 o^ 4 = v/jjii 4 v /v/gtij . oUgJui -f- ri 2 vy 



\co/ \co/ 



X co \ X co \ 



C 6 H 4\ /C 6 H 3 . SO 3 Na + sNaOH + O = C 6 H 4 \ /C 6 H 2 (ONa) 2 + Na 2 SO 3 + 2H 2 O. 



\co< \co/ 



Alizarin forms dark red prisms melting at 290. It is almost in- 

 soluble in water, slightly soluble in alcohol. 



As a phenol it forms salts with alkalies ; the solution in caustic 

 soda has a violet colour ; the salts with the divalent and trivalent 

 metals are insoluble and of various colours ; these salts are the dyes 

 which colour the fabrics. 

 Purpurin. 



Purpurin or I, 2, 4-trihydroxy-anthra- 

 >H quinone is present in madder root with 

 alizarin and is made by oxidising alizarin 

 jo OH with manganese dioxide and sulphuric acid. 



It forms dark red needles which melt at 253; in dyeing it gives 

 yellower shades than alizarin. 



Anthropurpurin and Flavopurpurin 



CO OH CO OH 



CO 



are two other anthraquinone derivatives used as dyes. It may be noted that 

 only those derivatives containing two hydroxy groups in the i, 2 position 

 form dyes. 



Mention may finally be made of the following complex aromatic com- 

 pounds : 



fluorene. 



Phenanthrene 



Chrysene, 



