GLUCOSIDES 83 



Anthraquinone Xanthone 



Flavone 



\/ 



The red dyes which were formerly obtained from madder, the 

 powdered roots of Rubia tindoria, but are now almost wholly 

 artificially synthetized, consist of at least four different glucosides, 

 the organic group of which, in each case, is an hydroxy-deriva- 

 tive of anthraquinone. The most important of these is rubery- 

 thric add, composed of two molecules of glucose linked with one of 

 alizarin (1, 2, dioxyanthraquinone). Xanthopurpurin contains 

 1, 3, dioxyanthraquinone, which is isomeric with alizarin; and 

 rubiadin is a monomethyl (the CHa being in the 4 position), deriva- 

 tive of this compound. Purpurin is a glucoside of 1, 2, 4, trioxy- 

 anthraquinone. 



The soluble yellow pigments are generally glucosides of 

 hydroxy-derivatives of xanthone or flavone, known as oxyxan- 

 thones or oxyflavones. The sugars which are united to these 

 nuclei vary greatly, so that there are a great variety of yellow, 

 white, or colorless flavone or xanthone pigment compounds. 

 These compounds are almost universally present in plants. For 

 example, one typical set of examinations of the wood, bark, leaves, 

 and flowers of over 240 different species of tropical plants showed 

 that flavone derivatives were present in every sample which was 

 tested, the pigments being usually located hi the powdery coating 

 of the epidermis of the tissues. 



The following typical examples will serve to illustrate the com- 

 position and properties of the glucosides of this type. 



