CLASSIFICATION AND STRUCTURE OF FATTY ACIDS 17 



milk fats,22~" butter fat, 2"* and in egg-j^olk oil.^^ Bosworth and Brown," 

 however, feel that the evidence for the occurrence of palmitoleic acid in 

 milk fatty acids is doubtful. The vegetable phosphatides contain 5 to 

 10% of this fatty acid.^^ Riebsomer and Johnson-^ found as much as 35% 

 of the unsaturated acids of Lycopodium clavatum (ground pine) spores to 

 consist of palmitoleic acid, and 60% of 9-octadecenoic acid, while another 

 primitn^e form, a sea alga (Cystophylhwi hakodatense Yendo), has been 

 shown to contain more than 20% of palmitoleic acid.^*' 



d. Other Monoethenoid Acids. The chief sources of the other mono- 

 ethenoid acids are the marine oils. Thus, the head oil of the sperm whale 

 {Physeter macrocephalus) contains decenoic, dodecenoic, and tetradecenoic 

 acids, while 9-eicosenoic acid, or gadoleic acid, has been reported in cod 

 liver oil, whale, herring, and sardine oils. It may also be obtained from 

 many other marine sources. The elasmobranch fish oils contain one of 

 the C24 monoethenoid acids, 15-tetracosenoic acid, while a hexacosenoic 

 acid has been reported in the body oil of the castor oil fish. Milk fat is the 

 source of fats of the Cw, C12, and C18 series. Erucic acid, 13-docosenoic 

 acid, makes up 40 to 50% of rapeseed, mustardseed, and wallflow^erseed 

 oils, while it almost completely accounts for the fatt}^ acid content of 

 nasturtium oil (80%). 



(4) Polyethenoid Adds 



The acids which have more than one double bond are of great importance 

 in animal nutrition, as well as for industrial uses. They include the so- 

 called "essential" fatty acids which are required by the animal since they 

 cannot be synthesized from other fatty acids or from carbohydrates. They 

 are of considerable importance in the paint industry, as well as w^herever 

 drying oils are employed. Moreover, it is by virtue of the relative ease 

 with which such acids can be hydrogenated that the margarine and vege- 

 table shortening industries have been able to develop. 



Only one representative of the diethenoid series is found ordinarily in 

 fats. It is linoleic acid, CH3CCH2)4CH:CHCH2 CH:CH(CH2)7COOH, 

 which has the empirical type formula C„H2„_402. Three triethenoid acids 

 are fairly common, one of which is a Cie (hiragonic) and the other two ds 

 acids (linolenic and elaeostearic). These have empirical formulas of 

 C„H2n-60':. Of the two tetraethenoid acids, arachidonic acid is better 

 known as a component of depot fats. Two more highly unsaturated acids 



26 F. Trost and B. Doro, Ann. chim. appUcata, 27, 233-242 (1937); Chem. AbsL, SI 

 8233 (1937). 



" A. W. Bosworth and J. B. Brown, J. Biol. Chem., 103, 115-134 (1933). 

 2» T. P. Hilditch and W. H. Pedelty, Biochem. /., 31, 1964-1972 (1937). 



29 J. L. Riebsomer and J. R. Johnson, J. Ayn. Chem. Soc, 55, 3352-3357 (1933). 



30 E. Takahashi, K. Shirahama, and N. Ito, /. Chem. Soc. Japan, 59, 622-666 (1938). 



