II, CHEMISTRY 187 



phase is more pronounced, while the color play frequent with other sterols 

 is usually absent. 



Ergosterol is insoluble in water,^^^ but the presence of 0.2 % of water in 

 ethyl acetate is claimed-^^ to increase its solubility in the latter solvent. 

 Weak aqueous colloidal solutions can be made by means of a mutual solvent 

 such as acetone, or by the action of supersonic waves, or with the aid of 

 dispersing agents. Better colloidal solutions can be made by dissolving the 

 sodium, potassium, or ammonium salts of ergosteryl acid esters, e.g., the 

 monoergosteryl esters of phthalic,^^^ • ^^^ succinic,^^^ and especially n-butane- 

 1 ,2,3,4-tetracarboxylic-®*' acids. 



Ergosterol is sparingly soluble in methyl formate and in methanol, which 

 makes these low-boiling liquids useful for washing ergosterol crystals in 

 analytical procedures, and for recovering unconverted ergosterol from crude 

 irradiation resin. Ergosterol is soluble in most organic solvents and in oils 

 and fats. Examples of its solubility in certain solvents are given in Table V. 



The stability of ergosterol in different solvents varies. Alcoholic solutions 

 keep for several weeks if stored in a dark place. Pyridine favors decomposi- 

 tion and oxidation. ^^ Ethylene dichloride is unsuitable because of the dif- 

 ficulty of keeping it free from traces of hydrogen chloride,^* to which er- 

 gosterol is very sensitive. Chloroform, which is so widely used for the 

 determination of the specific rotations of organic compounds that it may 

 be said to be the solvent of first choice, must be used with caution for ergos- 

 terol. Hydrated ergosterol dissociates in chloroform, giving the unstable 

 anhydrous sterol and a quantity of free water sometimes sufficient to create 

 turbidity and optical unfitness. -^^ Moreover, a solution of ergosterol in 

 chloroform discolors in a week, and if exposed to daylight it becomes brown 

 in a few hours.-^^- ^*^ Chloroform intended for optical test solutions should 

 be tested for traces of hydrogen chloride, which might induce isomeriza- 

 tion.2^' Any solvent subject to peroxide formation, such as acetone or ether, 

 should, on general principles, be removed from ergosterol crystals to pre- 

 vent the possible initiation of destructive changes. 



Ergosterol is strongly levorotatory, more so, in fact, than any sterol 

 likely to be associated with it. Consequently its rotation is a reliable index 

 of purity. On this basis it would seem that the preparations of Callow^* 

 and Huber et alP'^ are the purest ever described. Ergosterol does not 

 exhibit mutarotation (in chloroform) .-^^ Its rotation is more influenced than 

 that of sugars by the wavelength employed, and it is also greatly influenced 

 by the solvent. Data on these factors, obtained by Bacharach el al?^^ with 



2"aM. Sumi, Sci. Papers Inst. Phys. Chem. Research Tokyo 30, 252 (1936). 



"8 H. Emerson and F. W. Heyl, J. Am. Chem. Soc. 52, 2015 (1930). 



"9F. Hoffmann-La Roche and Co., German Pat. 495,450 (1930). 



260 R. Schonheimer and F. Breusch, Hoppe-Seyler's Z. physiol. Chem. 211, 19 (1932). 



