May 13, 191S Chemistry of the Cotton Plant 347 



IsoQUERCiTRiN (j) crystallizes from pyridin and water in pale- 

 yellow needles that melt at 217° to 219° C, are almost insoluble in cold 

 water, sparingly soluble in boiling water. The acetyl derivative is 

 much more soluble in alcohol than that of quercimeritrin. By hydroly- 

 sis both glucosids are split into quercetin and dextrose. Isoquercitrin 

 is more easily hydrolyzed than is quercimeritrin. 



Quercetin, a product of hydrolysis of quercimeritrin and iso- 

 quercitrin, is a flavone derivative to which the following formula has 

 been assigned by various investigators {10): 



O H 



II ^— ^ 

 -C— c 



^H 6dH 



Quercetin (9) has been found quite abundantly in various plants, 

 either free or combined. Since some of these quercetin compounds 

 are easily hydrolyzed, the finding of free quercetin may often be due 

 to the occurrence of hydrolysis during the extraction. Most of the 

 quercetin compounds are glucosids, the nature of the glucosid depend- 

 ing on the sugar groups with which quercetin is combined and also on 

 the place of linkage. Among such glucosids not occurring in the cotton 

 plant, quercitrin (9), rutin (9), and serotrin (6) have been isolated. 

 The sugars obtained by the hydrolysis of these glucosids are dextrose 

 and rhamnose. 



Quercetin crystallizes from aqueous solutions with two molecules of 

 water in fine needles of a bright-5'ellow color. It melts with partial 

 decomposition at about 310° C It is only slightly soluble in boiling, 

 and almost insoluble in cold water. 



The solubility in boiling alcohol is i to 18, being more than 10 times 

 the solubility in cold alcohol. The acetyl derivative crystallizes in 

 colorless needles that melt at 194°. 



GossYPiTRiN^ (j), another glucosid found in cotton, has the for- 

 mula C21H20O13. It crystallizes in small glistening needles of an orange- 

 yrllow color and melts at 2oo-202°C. 'It is only slightly soluble in 

 water and alcohol. The acetyl derivative crystallizes from acetic an- 

 hydrid and alcohol in colorless needles melting at 226° to 228° C. They 

 are almost insoluble in alcohol. 



'There is some confusion in the literature concerning the melting point of quercetin, some authors (7 

 p. 524) stating that it melts at 251° C, others (5, p. 813) at 310° . The writers found that their quercetin 

 melted at 310°. The same was true of a commerical sample. Both of these samples of quercetin 

 gave acetyl-quercetia melting at 194°. 



^ The presence of this glucosid in Hibiscus sabdariffa and Thespasia lampas has been reported by Schmidt, 

 but the authors have been unable to locate the original references. (Schmidt, Ernst, ausfuhrliches 

 tEHRBUCH DER PHARMAZEUTiscHEN CHEMIB. Aufl. 5, Bd. 2, p. 2040. Braxmschweig, 1911.) 



