GLUCOSIDES 85 



meric with similar flavone and xanthone derivatives, and the 

 transition from one color to the other in plants takes place very 

 easily under the action of oxidizing or reducing enzymes. This 

 accounts for the change of reds and blues to yellows and browns, 

 and vice versa, under changing temperature conditions. 



The following red or blue plant pigments, which are anthocyan 

 glucosides, have been isolated and studied (for the structural 

 arrangement of the characteristic groups, see pages 116): from 

 cornflower and roses, cyanin, C28HsiOi6Cl (2 molecules glucose 

 -fcyanidin); from cranberries, idain, C2iH2iOioCl (galactose 

 -fcyanidin); from geranium, pelargonin, C27H3oOi5Cl (2 mole- 

 cules glucose -f pelargonidin); from pseony, pceonin, C2sH33Oi6Cl 

 (2 molecules glucose +paeonidin, a monomethyl cyanidin); from 

 blue grapes, oenin, C23H25Oi2Cl (glucose -foenidin) ; from whortle 

 berry, myrtillin, C22H 2 3Oi2Cl (glucose -f myrtillidin) ; from lark- 

 spur, delphinin, C^HsgC^iCl (2 molecules glucose +2 molecules 

 p-oxybenzoic acid+delphinidin); and from mallow, malvin, 

 C29H3sOi7Cl (2 molecules glucose +malvidin). 



The blue dye, indigo, is derived from a glucoside of an entirely 

 different type, known as indican. Indican is readily extracted 

 from the leaves of various species of indigo plants. When hydro- 

 lyzed, it yields glucose and indoxyl (colorless). Indoxyl is easily 

 oxidized to indigotin (the deep blue dye known as " indigo ") 

 The equations illustrating these changes are as follows: 



(a) Ci 4 Hi 7 6 N + H 2 = C 6 Hi 2 O 6 + C 8 H 7 ON 



Indican Glucose Indoxyl 



(6) 2C 8 H 7 ON + O 2 = Ci 6 Hi O 2 N + 2H 2 O 



Indoxyl Indigotin 



The structural relationships of indoxyl and indigotin may be 

 illustrated by the following formulas: 



Indigotin 



o o 



i i x I j 



>N/ \ N / \/ 



I I 



H H 



