788 XIII. ESSENTIAL FATTY ACIDS 



Abu-Nasr, Potts, and Holman^^ employed the urea inclusion technic in 

 an effort to prepare fatty acids having four, five, or six double bonds from 

 marine fish oil. Although they were unsuccessful, they did obtain frac- 

 tions with iodine numbers as high as 356. 



d. Preparation from Bromo-Derivatives. One of the most widely used 

 procedures for the preparation of certain polyimsaturated acids is by decom- 

 position of the corresponding bromo-derivatives. Under certain condi- 

 tions, when the double bonds are saturated by bromination, the halogen 

 compounds possess solubility differences in organic solvents which permit 

 their isolation.^* 



However, at least two drawbacks have been ascribed to the use of this 

 procedure for the preparation of the EFA. Thus, in the first place, Fran- 

 kel and Brown ^'^ showed that the unsaturated acids formed after debromina- 

 tion consist of mixtures of cis- and trans-isomers. Since the geometrical 

 isomerization is an important factor in establishing whether or not a prod- 

 uct may possess biologic activity, this criticism merits most serious con- 

 sideration. A second difficulty associated with the use of the debromina- 

 tion method in the preparation of polyunsaturated acids is its limited 

 application. Thus, the procedure cannot be applied to acids which have 

 four or more double bonds, since these bromo-compounds are too insoluble 

 to allow their separation in a satisfactory manner from a solvent; moreover, 

 such polybromo-derivatives prove to be difficult to debrominate. Stein- 

 ]-)gj.g38 ]^^s found tetrahydrofuran useful for this purpose. 



e. Chromatographic and Related Methods. The only methods which 

 permit certain highly unsaturated acids to be obtained in a high degree of 

 purity in their natural form are the newer procedures of chromatography. 

 Elution analysis, frontal analysis, displacement analysis, partition chroma- 

 tography, and paper partition chromatography have all been employed. 



Partition chromatography has been used over the past decade for the 

 separation and analysis of volatile fatty acids, in which chloroform + 1% 

 butanol, along with silica gel, was the resolving mixture. ^^~^^ Moyle 

 et al.^" were able to effect the separation of a somewhat wider range of 



36 A. M. Abu-Nasr, W. M. Potts, and R. T. Holman, /. Am. Oil Chemists' Soc, 31, 

 16-20(1954). 



36 K. S. Markley, Fatty Acids, Interscience, New York, 1947, pp. 603 ff. 



"J. S. Frankel and J. B. Brown, J. Am. Chem. Soc, 65, 415-418 (1943). 



3* G. Steinberg, The Metabolism of the Essential Fatty Acids, Pli. D. Tliesis, Univ. Calif, 

 at Los Angeles, 1956. 



39 E. L. Smith, Biochem. J., 36, xxii-xxiii (1945). 



^"L. L. Ramsey and W. I. Patterson, J. Assoc. Offic. Agr. Chemists, 28, G44-656 

 (1945). 



^1 S. R. Elsden, Biochem. J., 40, 252-256 (1946). 



" V. Moyle, E. Baldwin, and R. Scarisbrick, Biochem. J., 32, 2178-2184 (1938). 



