184 VITAMIN D GROUP 



ethyl acetate-alcohol or in benzene-alcohol mixtures promotes the forma- 

 tion of large crystals.^^' Under the microscope ergosterol crystals are found 

 to be elongated six-sided prisms, the angles adjacent to the long sides 

 measuring about 127°, and the angles between the short sides 106°. The 

 extinction is parallel, the sign positive, and the plane of the optical axes 

 transverse to the length. The needles differ from the leaflets only in exag- 

 geration of length. It is somewhat uncertain whether the crystals are mono- 

 clinic or orthorhombic, but examination in convergent light suggests that 

 they are monoclinic.^^^' ^^^ 



Ergosterol usually contains one molecule of water of crystallization.**- ^*^' 

 246, 251 i^ retains this water so tenaciously that drying at room temperature 

 over sulfuric acid or calcium chloride removes only part of it.^*' ^^^ Tanret^^^ 

 apparently felt that ergosterol can be completely dehydrated without de- 

 composition by heating to 105° in a vacuum or in carbon dioxide (time not 

 specified, but presumably brief). The product thus obtained regains its 

 original weight after a few hours of exposure to air, but this is not the case 

 if it has become discolored. Callow** warns that the water "is difficult to 

 remove completely without decomposition." Bacharach ei alr^^ state that 

 "attempts to remove the water of crystallization by ordinary methods 

 involve some decomposition of the sterol." 



Tanret^^*' ^*^ noted that ergosterol oxidizes readily, especially in solution 

 or under the influence of warmth and light ; it becomes yellow and odorous 

 and its melting point and optical rotation are lowered. Callow** observed 

 that anhydrous ergosterol oxidizes more readily than does the hydrated 

 form. However, hydrated ergosterol, kept over calcium chloride and ex- 

 posed to air occasionally, took up five atoms of oxygen in the course of a 

 year, arriving at practically constant weight. The oxygen uptake curve was 

 that of an autocatalytic oxidation. The destruction of ergosterol is very 

 noticeable in hot solutions,^^®' ^^^^ -*i and it is probable that some damage 

 occurs whenever an ergosterol solution is heated, unless extraordinary pre- 

 cautions are taken to exclude oxygen. 



To preserve ergosterol, Tanret-^^ recommended that it be kept in a vac- 

 uum or under carbon dioxide. Callow** reported that in sealed tubes it 

 remains unchanged for long periods. Bills and Honey welP^^ found that 

 ergosterol, kept in the dark at 0°, remained colorless for a year, even though 

 exposed to air. However, Bacharach et al}^^ observed yellowing in a sample 

 kept in the dark at "a low temperature." It is the experience of industrial 

 users that ergosterol can be kept indefinitely in well-sealed bottles, which 

 have been gassed and stored in a cool, dark place. 



The melting point, or melting range, of ergosterol has never been satis- 

 factorily established. Callow** reported that the purest ergosterol, partially 



253 W. A. Carlson, U. S. Pat. 2,167,272 (1939). 



