334 



PIGMENTS 



Rhamnus cathartica and R. tinctoria, both of which are used 

 for dyeing cotton — 



OH 



CH,0 



OH 



OH 



Morin. — ^This substance, which is isomeric with quercetin, 

 occurs in the wood of Morus tinctoria (yellow wood) where it 

 is accompanied by another colouring matter, maclurin, some- 

 times called moritannic acid (see p. 280) — 



H0/\/°\ 



OH 



OH 



COH 



OH CO 



Luteolin. — This is the yellow colouring matter of Reseda 

 luteola, known as " weld " ; it is also contained in Genista 

 tinctoria or Dyer's broom — 



O OH 



HO 



c— 



11 



CH 



OH 



V 



OH CO 



Other members of this group of substances are Apigenin, 

 occurring in Apium petroselinum, and Fisetin, occurring in 

 Quebracho colorada, and Rhus cotinus or Dyer's sumach. 



The point of attachment of the carbohydrate residue has 

 as yet only been ascertained in the case of a few of the gluco- 

 sidal flavonols * ; thus in the case of quercitrin glucoside 

 exhaustive methylation yielded a pentamethyl ether which 

 on hydrolysis gave 5 : 7 '• 3' : 4' tetramethoxyfiavonol I. from 

 which it follows that the rhamnose was attached to the carbon 

 atom 3 as may be seen from the attached formulae : — 



* Attree and Perkin : " J. Chem. Soc," 1927. 234. 



