Wakeman—Pigments of Flowering Plants. 
853 
Rhamnetin, — Quercetin-3-monomethyl ether, or 
Trihydroxy-1, 3', 4'-methoxy -3-flavonol. 
CH s OC 
CH 
C — O— C-C 
II 
c - C — COH 
:oh 
HC 
CH CH 
M 
o 
COH 
Rhametin was known as early as 1841 in the form of gluco- 
side then called rhamnin 1 but now known as xanthorhamnin. 
It was hydrolized in 1858 by Gellatly, 2 and the sugar was identi¬ 
fied as rhamnose by Berend 3 in 1878. Later Tanret 4 found 
that xanthorhamnin was a mixed glucoside containing two mole¬ 
cules of rhamnose and one of galactose. The constitution 5 of 
rhamnetin and other methyl ethers of quercetin has been the 
subject of considerable chemical study, the question under con¬ 
sideration being the position of the methoxy groups. Perkin, 6 
in 1902 showed that by careful decomposition with alkalies the 
monomethyl ether of phloroglucin is obtained and that the 
methoxy group must therefore be in that part of the molecule 
from which the phloroglucinol is obtained. The formula for 
rhamnetin according to Perkin is given above. 
According to Czapek, rhamnetin occurs as the glucoside in the 
fruit and in the bark of several species of Rhamnus. Kane, 7 
Gellatly, 8 Schuetzenberger, 9 and Liebermann 10 find it in the 
“Gelbeern” or * ‘ Avignonkoerner, ’ ’ the fruit of Rhamnus in- 
fectoria and R. tinctoria. 
Rhamnetin crystallizes best from phenol, in which it is easily 
soluble when heated. It separates on cooling in small bright 
lemon yellow crystals. It is sparingly soluble in warm water 
and very slightly soluble in the ordinary organic solvents. It 
1 Jr. Chem. Soc., 27, p. 666. 
2 Chem. Centrlbl., 29, p. 477. 
8 Ber., 9, p. 1353. 
4 C. r., 129, p. 725; Bull. Soc. Chim., (3) 21, p. 1073. 
6 Monats., 4, p. 889; 9, p. 548; 10, p. 561. 
* Jr. Chem. Soc., 81. p. 569. 
7 Berz. Jahresb. 24, 505. 
8 Jahresb., 1838, p. 474. 
"Jahresb., 1868. p. 774. 
10 Ann.. 196. p. 313. 
