II. CHEMISTRY 195 



ciferol or precalciferyl 3 , 5-dinitrobenzoate is held at G0° for several hours 

 in the dark, the dextrorotation increases to almost that of calciferol or 

 calciferyl 3, 5-dinitrobenzoate, and the latter products can be isolated. 

 Conversely, solutions of calciferol or calciferyl 3 , 5-dinitrobenzoate produce 

 some precalciferol or precalciferyl 3, 5-dinitrobenzoate. In any of these 

 solutions, calciferol always predominates at equilibrium. The relationship of 

 the two isomers is presumed to be a phenomenon of transitory cyclization. 

 The increasing dextrorotation in the Windaus and Auhagen^**' experi- 

 ment, heretofore unexplained, was probably due to the precalciferol-cal- 

 ciferol transformation, which was overshadowed spectrally by the simul- 

 taneously occurring protachysterol-tachysterol transformation. Thus it 

 appears that there are two dark reactions in the activation series. 



Mention should be made of the claim by Raoul et al}^'^ that, in ionizing 

 solutions, calciferol and tachysterol are interchangeable. It was found that 

 in an ionizing agent such as symmetrical dichloroethane, activated with 

 1 % glycerol dichlorohydrin, calciferol undergoes a change, its optical prop- 

 erties simulating those of tachysterol. If the ionization is checked before it 

 has continued too long, the product reverts to calciferol, but if it has been 

 prolonged, the change l)ack to calciferol can be brought about only by 

 irradiation. That the product into which the calciferol changed was really 

 tachysterol may be ciuestioned, since it was reported that an attempt to 

 prepare the 3,5-dinitro-4-methylbenzoate of tachysterol resulted only in 

 the formation of the corresponding ester of calciferol. 



/. Calciferol. Vitamin Do. Ergocalciferol 



C28H44O. Four double bonds. Melting point 121°.2^'' Distils, with de- 

 composition, at 150° in high vacuum.-'*' Broad absorption band with maxi- 

 mum at 265 m/i; molecular extinction coefficient = 19,400 in alcohol 

 (El'^^m. = 490) .29«- 290a [^]2o _ 4-106°, [a]fiQ, = +125° (in absolute alco- 

 hol) .2« 



In 1930-1931 the English and German teams of investigators succeeded 

 in isolating pure xdtamin D from the irradiation resin of ergosterol. An 

 ingenious method for the distillation and fractional condensation of the 

 resin in a high vacuum was described by Askew ei al.-^^ Small amounts of 

 potent crystals were obtained. The method was improved, and a detailed 

 study of the active crystals was reported by Angus ei al.^'^^ The name, 

 calciferol, was given to the crystalline substance. A few months later, in 

 1931, Askew et al.^^^ discovered that the original calciferol was a mixture, 



289 Y. Raoul, J. Chopin, P. Meunier, and N. Le Boulch, Compt. rend. 228, 1064 (1949). 

 29» H. P6nau and G. Hagemann, Helv. Chirn. Acta 29, 1366 (1946). 

 290" S. K. Crews and E. L. Smith, AnaUjst 64, 568 (1939). 



"1 F. A. Askew, R. B. Bourdillon, H. M. Bruce, R. G. C. Jenkins, and T. A. Webster, 

 Proc. Roy. Soc. (London) B107, 76 (1930). 



