ROLE OF BILE IN LIPID ABSORPTION 103 



Unsaturated and halogenated acids usually have the same coordination 

 numbers as do the saturated acids having the same number of carbons. 

 Crotonic acid, the simplest unsaturated acid studied, combines with 3 

 bile acids, while butyric acid, the saturated acid with the same number of 

 carbon atoms, forms choleic acids with 2 or 4 desoxycholic acids, depending 

 upon the method of preparation. 526 The cis and trans isomers, oleic and 

 elaidic acids, 630 have the same coordination value (8) as stearic acid. 606,631 

 Such alicyclic ring acids as hydnocarpic and chaulmoogric behave in the 

 same manner as the corresponding straight-chain acids. 532 



In the case of the dicarboxylic acids, glutaric (C 5 ) acid fails to form a co- 

 ordination compound, although data are not available on the two simplest 

 acids in this series (oxalic and malonic) . Dicarboxylic acids having 7 to 1 1 

 carbons (5-9 — CH 2 — groups) combine with four bile acid molecules, 

 while no coordination numbers higher than 6 have been observed in the 

 higher acids (even up to C 23 ) . 



A large group of simple esters have been examined by Rheinboldt, 

 alone 533 and with Konig and Otten. 534 These investigators found that an 

 alcohol with n carbons has the same coordination number as does an acid 

 with (n + 1) carbon atoms. In the alkyl esters of the aliphatic acids, the 

 coordination number corresponds to the value characteristic of the longer 

 of the two chains. In most cases where the acyl and alkyl groups have the 

 same coordination number, the ester will have the next higher coordination 

 value. Thus, in the case of butyl valerate and amyl caproate, in which 

 both alkyl and both acyl groups, when present as free alcohols or acids, 

 have a coordination number, of 4, there are six bile acid components in the 

 choleic acid molecules of the esters. Triolein has been shown to yield 

 choleic acid 535 melting at 184-185°C, but the coordination number is 

 uncertain. Sobotka and Kahn 536 ' 537 reported a figure of 3 for the coordina- 

 tion value of the choleic acid derivative prepared from ethyl acetoacetate, 

 which melts at 154°C. 



It is surprising that choleic acid derivatives of many hydrocarbons, both 

 aliphatic and cyclic, can be readily prepared. A coordination number of 8 



630 W. Marx and H. Sobotka, /. Org. Chem., 1, 275-279 (1939). 



631 H. Rheinboldt, H. Pieper, and P. Zervas (with M. Kircheisen), Ann., 451, 256-273 

 (1927). 



532 A. P. Buu-Hoi, Z. physiol. Chem., 278, 230-235 (1943). 



533 H. Rheinboldt, Ann., 451, 256-273 (1926). 



534 H. Rheinboldt, O. Konig, and R. Otten, Ann., 478, 249-259 (1929). 



635 A. W. Downie, L. Stent, and S. M. White, Brit. J. Exptl. Pathol., 12, 1-9 (1931). 



636 H. Sobotka and J. Kahn, Biochem. J., 26, 898-904 (1932). 



637 H. Sobotka and J. Kahn, Ber., 65, 227-232 (1932). 



