598 VI. CAROTENOIDS AND RELATED COMPOUNDS 



Aschoff^" investigated the saffron pigment as early as 1818, and gave it 

 the name "crocin." Although the glucosidic nature of crocin became 

 evident through the work of a number of investigators in the last half of 

 the 19th century,^""^^^ the isolation of the aglucone crocetin was not 

 accomplished until 1914 when Decker*" succeeded in obtaining it. The 

 constitutions of crocin and of crocetin have been elucidated mainly through 

 the work of the Karrer group.^^-*'*^'*^^"*^^ 



Crocetin exists in both the stable and the labile forms, although only one 

 example in the latter category is recognized. The relationship of the 

 several compounds and their terminology are indicated in Table 1 1, page 595. 



a. Crocetlns. Two stereochemical crocetin isomers (labile and stable) 

 exist, as is the case with bixin. According to the recent work of Kuhn 

 and L'Orsa,''^ they have an empirical formula of C20H24O4, although a num- 

 ber of the earlier workers'^-*^^-'*®^ assigned to them a composition repre- 

 sented by the formula Ci9Hi204. The polyene nature of the saffron pig- 

 ments was first recognized by Karrer and Salomon.^- They demonstrated 

 that the perhydro compound, obtained by catalytic hydrogenation, is a 

 saturated, completely aliphatic dicarboxylic acid. On the basis of strong 

 absorption in the ultraviolet region, as well as the extensive production of 

 glyoxal on ozonolysis, it can be concluded that the double bonds are con- 

 jugated. On decomposition with chromic acid, 4 molecules of acetic acid 

 are produced, indicating the presence of that number of methyl groups 

 attached as side chains. Two additional carbons are accounted for as 

 present in carboxyl groups. This leaves 14 carbons present in the alipha- 

 tic chain; these undoubtedly account for the 7 double bonds which are 

 known to exist. The unsymmetrical structural formula proposed by Kuhn 

 and L'Orsa''^ is probably incorrect. There are several reasons for accepting 

 the synmietrical formula proposed by Karrer and his collaborators.'***'*" 



CH3 CHj CHj CH3 



^J^IhhhIhhhhIhhhI? 

 HOC •c:C-c:C'C:C'C:C'C:C'C:C'C:C- C— OH 



Crocetin 



«2 Aschoff, Berl. Jahrhuch Pharm., SI, 142 (1818). Cited by P. Karror and E. Jucker, 

 Carotinoide, Birkhauser, Basle, 1948, p. 279. 



""B. Quadrat, /. prakt. Chem., 56, 68 (1852). Cited l)y I^ Karrer and E. Jucker, 

 Carotinoide, p. 279. 



«4 R. Kayser, Ber., 17, 2228-2234 (1884). 



«5 E. Fischer, Ber., 21, 988-991 (1888). 



«6 E. Schunck and L. Marchlewski, Ann., 278, 349-3.59 (1894). 



«^ F. Decker, Arch. Pharm., 252, 139-160 (1914); Chem. Ah.st., S, 3416 (1914). 



«8 p. Karrer and H. Salomon, Helv. Chim. Ada, 10, 397-405 (1927). 



«9 P. Karrer and H. Salomon, Helv. Chim. Acta, 11, 711-713 (1928). 



«" P. Karrer and H. Salomon, Helv. Chim. Acta, 16, 643 (1933). 



«i P. Karrer and K. Miki, Helv. Chim. Acta, 12, 985-986 (1929). 



«2 P. Karrer and A. Helfenstein, Helv. Chim. Acta, 13, 392-397 (1930). 



«3 p. Karrer, F. Benz, and M. Stoll, Helv. Chim. Acta, 16, 297-302 (1933). 



