86 II. CHEMISTRY OF FATTY ACIDS AND GLYCEROL 



has recently been confirmed. ^^^^^^ Ricinelaidic acid was prepared by this 

 method by Playfair-^^ and others. 2^^~*'"' Nitric acid, usually in dilute 

 solution, has also been employed (Haussknecht,^"^ Keffler and Maiden ^''^) 

 to bring about the isomerization. 



In addition to the nitiogen oxides, sulfurous acid is an active catalyst. 

 Saytzeff^"^ obtained a transformation of oleic to elaidic acid with sulfurous 

 acid or sodium bisulfate. In the case of erucic acid, the transformation can 

 be effected in 24 hours at 200° C. Phosphorous acid acts catalytically in a 

 manner similar to that of sulfurous acid,^"* while Rankoff^"^-^"^ has suc- 

 cessfully used sulfur or phosphorus. 



Bertram 307-309 proposed the use of selenium, and this has turned out to 

 be one of the best agents to effect such transfoimations. An equilibrium 

 mixture of triolein and trielaidin can be produced in 8 hours with 0.3% 

 selenium at 150-220°C. In addition to selenium itself, hydrogen selenide, 

 selenium dioxide, and selenium dibromide are active. The closely related 

 element, tellurium, has been tested by Bertram, and it is also potent. 



The elaidinization reaction is a reversible one. In the case of the oleic 

 acid ^ elaidic acid change, equilibrium is reached when the mixture con- 

 tains 34% of oleic acid and 66% of elaidic acid. The point of equilibrium 

 is independent of the catalyst, and results irrespective of whether one starts 

 with the CIS or the trans form. 



c. Isomers of Oleic Acid. There are a number of positional isomers of 

 oleic acid, as well as an additional geometric isomer for each compound. 

 Not all of these potential compounds have been prepared. 



Among the six known cis isomers, petroselinic acid, CH3(CH2)ioCH:- 

 CH(CH2)4COOH, and oleic acid, CH3(CH2)7CH:CH(CH2)7COOH, are 

 best known. The other related acids are 2-, 3-, 4-, and 12-octadecenoic 

 acids. 



Eight trans isomers have been studied. These include three well-kno\\'ii 

 compounds, petroselaidic acid (the trans form of petroselinic acid), elaidic 

 acid (related to oleic acid), and vaccenic acid, CH3(CH2)5CH:CH(CH2)9- 



2" T. G. Green and T. P. Hilditch, Biochem. J., 29, 1552-1563 (1935). 



298 L. Playfair, Phil. Mag. [3], 29, 475^80 (1846). 



299 F. Kj-afft, Ber., 21, 2730-2737 (1888). 



300 C. Mangold, Monatsh., 15, 307-315 (1894). 



301 O. Haussknecht, Ann., US, 40-57 (1867). 



302 L. Keffler and A. M. Maiden, Bull. soc. chim. Belg., U, 467-472 (1935). 



303 M. Saytzeff, C. Saytzeff, and A. Saytzeff, /. prakt. Chem. [2], 50, 73-80 (1894). 

 30* S. Fokin, /. Russ. Phys. Chem. Soc, 42, 1068-1073 (1910); Chem. Abst., 5, 3923 



(1911). 



305 G. Rankoff, Ber., B62, 2712-2717 (1929); B64, 619-621 (1931); B69, 1231-1238 

 (1936). 



306 G. Rankoff, Ber., 63, 2139-2142 (1930). 



307 S. H. Bertram, Chem. Weekblad, 33, 3-5 (1936); Chem. Abst., SO, 3405-3406 (1936). 



308 S. H. Bertram, U. S. Patent No. 2,165,530 (July 11, 1939). 



309 S, H, Bertram, Rec. trav. chim., 59, 650-652 (1940). 



