PROPERTIES OF VITAMINS D 



779 



In hcxane or diethyl ether, vitamin D2 has an absorption maximum at 

 265 mM^"^ and an absoiption minimum at 310 mju. The molecular extinc- 

 tion coefficient (e) is 18,200'°^ while the value for E (1%, 1 cm.) equals 

 4g0i59.247 2^^ 265 m/x; the figures are both at the minimum point on the 

 curve (310 vaij). The complete absorption curve is given in Figure 7. 



mm" 



350 mjuL 



Fig. 7. The absorption spectra of vitamin D2 (O — O) and of vitamin 

 D, (A- -A) in 0.02% solution in hexane.85'Bi K = 45 to 46 X 10^ 



Two crystalline esters of vitamin D2 can be readily prepared. These in- 

 clude the 3,5-dinitrobenzoate, which melts at 148-149°C. and has an optical 

 rotation ([ajo) in benzene of +55°. The second common ester is the p- 

 nitrobenzoate, which melts at 93°C., and has a specific rotation, ([q:]d) of 

 -f-104° in chloroform. 



Crystalline vitamin D2 is stable over long periods when stored in the dark 

 in sealed tubes from which oxygen has been excluded. It is also quite 

 stable when dissolved in olive oil and stored under similar conditions. 

 After 5 years, more than 50% was found to be still present. 



Vitamin D2 is destroyed by heat. In spite of the fact that it can be sub- 

 limed at 125°C. if a high vacuum is employed, it is partially decomposed 

 into pyrocalciferol and isopyrocalciferol, although these decomposition 



2" S. K. Crews and E. L. Smith, Analyst, 64, 568-570 (1939). 



