104 II. DIGESTION AND ABSORPTION OF FATS 



appears to be the maximum, even in the case of tritetracontane, which 

 contains 43 carbons. 831 



The ability to form choleic acids is apparently related to the solubility 

 of the complex in the solvent employed. Ethyl alcohol is usually used with 

 desoxycholic acid because it forms a labile complex from which the acid 

 can be recovered by prolonged drying in a vacuum. Xylene gives a similar 

 complex with desoxycholic acid which is more stable than the alcohol com- 

 plex; in fact, the xylene will displace the ethyl alcohol from the choleic 

 acid. Finally, the acetic acid choleate is more stable than is xylene- 

 choleic acid ; acetic acid will displace xylene from its combination. 



Cyclic hydrocarbons form compounds with desoxycholic acid, but the 

 number of molecules added is much smaller than is the case when straight- 

 chain hydrocarbons having the same number of carbons are employed. 

 For example, naphthalene and acenaphthene 529 form compounds with a 

 coordination value of 2, phenanthrene 529 one of 3, and anthracene 630 one of 

 4. On the other hand, Fieser and Newman 629 did not obtain choleic acids 

 when chrysene, 1,2-benzpyrene or several related hydrocarbons were em- 

 ployed in alcoholic solutions. 



(e) Apocholic Acid Complexes. Desoxycholic acid is the only one of the 

 natural bile acids which possesses the ability to form choleic acids. How- 

 ever, Boedecker alone 538 and in association with Volk 539 discovered that 

 apocholic acid, an unsaturated derivative of desoxycholic acid, is able to 

 combine with acids and hydrocarbons in a manner analogous to that of 

 desoxycholic acid. Two forms of apocholic acid were shown to be active, 



COOH 



HO H 



(XI) Apocholic Acid 



ol- (or simply apocholic) and /3-apocholic acid. The mild dehydration of 

 cholic acid with anhydrous zinc chloride in acetone solution gives a 75% 

 yield 540 of apocholic acid; when carried out in acetic acid solution the yield 



"»F. Boedecker, Ber., 63, 1852-1862 (1920). 



539 F. Boedecker and H. Volk, Ber., 64, 2489-2492 (1921). 



540 A. W. Devor and H. W. Marlow, /. Am. Chem. Soc, 68, 2101 (1946). 



