212 VITAMIN D GROUP 



Concentrated preparations of vitamins D2, D3, and D^ are produced in 

 a much greater total unitage than fish oils for medicinal use and animal 

 feeding. The manufacture of fish oils has continued at a high level because 

 of their importance as a source of vitamin A, but since 1950, with the ad- 

 vent of synthetic vitamin A at low cost, the trend to replacement by syn- 

 thetics has been accelerated. The end use, as well as the source, of vitamin D 

 has undergone great change. In 1925 vitamin D, then almost solely in the 

 form of cod liver oil, was used principally to cure rickets in children. By 

 1950 florid rickets had become a rarity, thanks to the use of vitamin D in 

 many forms to 'prevent it. During the same period, the use of vitamin D in 

 poultry raising expanded from the experimental stage to the principal field 

 for this vitamin. 



The first synthetic vitamin D manufactured in the United States was 

 produced by pumping a peanut oil solution of ergosterol through the cooling 

 jacket of a quartz mercury vapor lamp and then through a heat exchanger, 

 cyclically, until the desired conversion was effected.^ A more efficient unit, 

 employing the carbon arc, and designed to activate provitamins D in 

 transparent solvents, is shown in Fig. 15. This unit, still in use after more 

 than twenty years, has a daily capacity of the equivalent of 8 metric tons 

 of cod liver oil. In a different arrangement, shown in Fig. 16, the solution 

 flows through a series of activating units, each containing a water-cooled 

 Hanovia lamp and an outer quartz chamber for the provitamin D solution. 



In commercial practice, ether is usually the preferred solvent. The irradia- 

 tion is continued until a certain percentage of the provitamin is transformed, 

 the exact amount being determined for optimum vitamin yield under the 

 conditions of exposure, particularly the type of light source and the kind 

 of provitamin. Usually not over 50% transformation is allowed. The un- 

 changed provitamin is recovered by evaporating the solvent, taking up the 

 resin in methanol, and freezing out. After the methanol is removed, the 

 resin is either dissolved without further treatment in an edible oil, or it is 

 converted into 3 , 5-dinitrobenzoate for the preparation of crystalline vita- 

 min D. 



Some manufacturers use light filters, and others do not. The advantages 

 in yield gained by using light of about X 280 m^i are more or less offset by 

 the loss of light, but filtered light is probably advantageous when minimal 

 accumulation of tachysterol is desired, as in the production of crystalline 

 vitamin D. Some choice of wavelengths is available to users of carbon arcs, 

 for carbons can be purchased with different core materials, and large users 

 can even have them made to order. The hot mercury arc differs spectrally 

 from the cold, but both are rich in the shorter waves, the cold especially so. 



It is customary to exclude oxygen during irradiation, either by using 



8 C. E. Bills, U.S. Pats. 1,808,760 (1931); 1,848,305 (1932). 



