PROPERTIES OF THE TOCOPHEROLS 813 



able to produce crystalline a- and 7-toeopherols from two highly jjurified 

 preparations of natural tocopherols.*^ He was unsuccessful, however, in 

 obtaining crystalline natural /S-tocopherol. The method employed for 

 crystallizing the a- and 7-tocopherols was by the use of a 2.5% methanol 

 solution at — 35°C. followed by drying at — 10°C. under a high vacuum. 

 The a- and 7-tocopherol crystals are pictured in Figures 2 and 3. 5- 

 Tocopherol has been obtained only as a yellow oil, although the p-phenyl- 

 azobenzoyl ester is crystalline.** 



In the absence of oxygen, the tocopherols are quite stable when heated 

 alone to 200°C. or to 100°C. in the presence of sulfuric or hydrochloric 

 acids. They are acted on by alkalies only slowly, and therefore may be ob- 

 tained by alkaline hydrolysis. The tocopherols are reasonably resistant to 

 destruction in visible light but are quite susceptible to alteration in ultra- 

 violet light. *''^^ They are all highly sensitive to oxidation, which causes a 

 disappearance of their biological activity. In general, such esters as the 

 succinates and acetates are more stable than are the free alcohols. 



The four tocopherols have similar characteristic absorption spectra in 

 the ultraviolet with maxima in the neighborhood of 295 m^.*^ Olcott^^-*^ 

 was the first investigator to call attention to this property. He placed the 

 band at 294 m/x. The latter figure was confirmed shortly thereafter by 

 Martin and associates,^^ as well as by Drummond et al.^^'^'' This maximum 

 is displaced to approximately 285 m^u for such esters as the acetates. The 

 extinction coefficient, E (1%, 1 cm.), for the free a-tocopherol is reduced 

 from 77 to 42 when changed to the allophanate ester. ^'*<' The absorption 

 maximum of 6-tocopherol was reported to be 298 van. E (1%, 1 cm.) was 

 found'^ to be 91.2. The absorption spectrum of a-tocopherol in iso-octane 

 is given in Figure 4. A similar absorption pattern obtains for /3-to- 

 copherol.^"' Data on the characteristic absorption of a-tocopherol are also 

 given in Table 5. 



TABLE 5 

 Absorption Characteristics of a-TocoPHEROL in Iso-octane" 



" O. H. Emerson, G. A. Emerson, A. Mohammad, and H. M. Evans, /. Biol. Chem., 

 122, 99-107 (1938). 



97 J. C. Drummonci, E. Singer, and R. .J. Mac Walter, Biochem. J., 29, 2510-2521 

 (1935). 



98 H. S. Olcott, J. Biol. Chem., 105, Ixv (1934). 



99 A. J. P. Martin, T. Moore, M. Schmidt, and F. P. Bowden, Nature, 134, 214 (1934). 

 '"o H. Rudy, "Chemie der Vitamine," in W. Stepp, Ernahrungslehre, Springer, Berlin, 



1939, pp. 108-166. 



10' F. Bergel, A. Jacob, A. R. Todd, and T. S. Work, Nature, HI, 646 (1938). 



