TWO CHEMICAL CONSTITUENTS FROM THE EUCALYPTS. 69 



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A typical example of this class is gentisin, the dye material 

 of gentian root (Gentiana lutea), and which has the con- 

 stitution of a dihydroxy monomethyl ether. 



The constitutional formula for quercetin — first suggested 

 by Herzig — is as follows :— 



O 



oh/ 



OH 



0— < > OH 



O'OH 



OH CO 



and this on heating in concentrated potash at 180 — 200°C. 

 for half an hour, breaks up into protocatechuic acid and 

 phloroglucinol. This method of decomposition has been 

 found most useful in determining the structure of the 

 several members of the quercetin group, and the position 

 of the hydroxyl radicles. It has been the information 

 gained in this way that has enabled the hydroxyls in morin 

 to be located. This substance is isomeric with quercetin, 

 the only difference being that the nucleus in morin is reso- 

 cinol instead of catechol as in quercetin, so that these two 

 hydroxyls in morin are in the meta position, whereas they 

 take up the ortho position in quercetin. 



It has been suggested 1 that the tinctorial property of 

 quercetin is due to the two distinct pairs of hydroxyl groups 

 in its molecule, but morin also dyes very well and is largely 

 used commercially as a dyestuff ; both molecules contain 

 one hydroxyl in the pyrone ring. 



1 Perkin and Martin— Trans. Chem. Soc, 1897, p. 821. 



