334 



IV. WAXES, HIGHER ALCOHOLS, ETC. 



The iodine absorption value, which is a function of the double bond, may 

 be useful in the identification of cholesterol. Hiibl reagent gives a theoret- 

 ical result (65.8), as does the Rosenmund-Kuhnhenn pyridine sulfate-bro- 

 mine reagent.^*" The Wijs and Hanus solutions, on the other hand, yield 

 erroneous values. According to Rolls, ^^* such irregularities in iodine ab- 

 sorption may be the result of variations in temperature or in the solvent 

 employed. Although the Rosemnund-Kuhnhenn reagent gives theoretical 

 results with cholesterol, the values are too high with ergosterol. ^^^ Bloor^'^^ 

 has indicated that when the latter reagent is modified by substitution of 

 iodine for bromine, it serves satisfactorily for the determination of ergos- 

 terol; the modified reagent no longer gives a theoretical result with 

 cholesterol. However, the original Rosenmund-Kuhnhenn reagent can be 

 employed satisfactorily with both cholesterol and ergosterol if the medium 

 is changed to one containing three parts of methanol and one part of acetic 

 acid. 



One important transformation which can be effected on the cholesterol 

 molecule is the introduction of a second double bond in ring B with the 

 formation of 7-dehydrocholesterol. This compound, which is found to 

 some extent in nature and presumably may be synthesized in limited 

 amounts by the higher animals, is of especial interest, since it has been 

 shown to be provitamin D3. The classical synthesis of this compound has 

 been accomplished by Windaus and his co-workers ^^^ by oxidation of choles- 

 teryl acetate with chromic acid to 7-oxycholesteryl acetate, followed by 

 reduction with aluminum isopropoxide. This yields 7-hydroxycholesterol. 

 The latter compound is benzoylated, and the dibenzoate is then decom- 

 posed by heat and by saponification into 7-dehydrocholesterol and benzoic 

 acid. These reactions are illustrated in the following equations: 



CHXOO 



Cholesteryl acetate 



"^ J. O. Rolls, ./. Am. Chem. Soc, 55, 2083-2094 (1933). 



"5 M. Yasuda, ./. Biochem. Japan, 25, 417-433 (1937). 



i'-'6 A. Windaus, H. Lettr6, and F. Schenck, Ann., 520, 98-106 (1935). 



