II. CHEMISTRY AND INDUSTRIAL PREPARATION 9 



of these carotenes will therefore clarify the chemical structure of all other 

 provitamin A carotenoids. It has already been shown hi Table I that these 

 three carotenes are isomeric, having the same empirical composition, C4oH66. 

 Furthermore, they are isomeric with Ija-opcue, which is devoid of provita- 

 min A activity. Theoretically a hydrocarbon of the above composition 

 should absorb 13 moles of hydrogen to form a saturated hydrocarbon of 

 the empirical composition C40H82. Only lycopene'' yields a hydrocarbon of 

 this composition, showing that it is an open-chain unsaturated hydrocarbon. 

 Catalytic hydrogenation of a-carotene'^ and /S-carotene'^ gives the same 

 perhydro compound, C40H78, showing the presence of two rings in each 

 carotene. T-Carotene,-" on the other hand, absorbs 12 moles of hydrogen to 

 yield perhydro-7-carotene, C40H80, showmg the presence of only one ring 

 in the orighial molecule. 



In addition to quantitative hydrogenation and spectroscopic examination 

 of carotenoids, degradative studies are essential for the complete elucida- 

 tion of their structure. Table III summarizes the products obtained when 

 lycopene and a-, (5-, and 7-carotenes are subjected to air oxidation, ozon- 

 olysis, hot chromic acid oxidation, alkaline permanganate oxidation, and 

 dry distillation. The last column shows the mam literature references. 



From the hydrogenation data, absorption spectra, and degradation prod- 

 ucts shown in Table III, the following conclusions may be drawn re- 

 garding the structure of the four carotenoids. Lycopene has thirteen double 

 bonds, eleven of which are conjugated and two isolated. Since 2 moles of 

 acetone are formed on ozonolysis, the isolated double bonds are attached 

 to isopropylidene groups, each of which is separated from the conjugated 

 system by a saturated residue which leads to the formation of succinic 

 acid. Since 7-carotene gives, on degradative oxidation, acetone and geronic 

 and succinic acids, it must have one trimethylcyclohexenyl nucleus similar 

 to that present in jS-ionone and an open chain similar to that present in 

 lycopene. j8-Carotene has eleven conjugated double bonds and two tri- 

 methylcyclohexenyl rings similar to that present in /3-ionone. a-Carotene 

 likewise has eleven double bonds, but its absorption spectrum, optical 

 activity, and degradation products indicated that one of the double bonds 

 is isolated in a trimethylcyclohexenyl ring similar to that present in a- 

 ionone. The other ring is of the |8-ionone type. Since the provitamin A ac- 

 tivity depends in part upon the presence of the j8-ionone nucleus, jS-caro- 

 tene which has two such nuclei shows twice as much biological activity as 



" P. Karrer and R. Widmer, Helv. Chim. Ada 11, 751 (1928). 

 '8 (a) J. H. C. Smith, ./. Biol. Chem. 102, 157 (1032). 



(b) R. Kuhn and E. F. Moller, Z. niujew. ('hem. 47, 145 (1934). 

 " L. Zechmeister, L. Cholnoky, and V. Vrabdly, Ber. 61, 566 (1928); 66, 123 (1935). 

 20 R. Kuhn and H. Brockmann, Ber. 66, 407 (1933). 



