CHEMICAL PROPERTIES OF FATTY ACIDS AND RELATED COMPOUNDS 151 



that a mixture of nickel and boron trioxide gives an active catalyst.®^' 

 Nickel silicate has been reported to be the most active nickel salt when com- 

 pared with the tungstate, borate, chromate, and molybdate salts.^^o 



Although platinum catalysts are not generally used in commercial opera- 

 tions, they are useful in laboratory-scale sjmtheses. They are less specific 

 than are the nickel catalysts. ^^^ Mixed catalysts containing platinum or 

 palladium and nickel®-^"^^* have been suggested. Platinum catalysts are 

 poisoned by hydrogen sulfide, phosphine, mineral acids, carbon disulfide, 

 chloroform, and liquid hydrocarbons. ^^^ 



(b) Mechanism of Catalytic Hydrogenation. When hydrogenation is 

 carried out with oleic acid, one mole of hydrogen is added per mole of oleic 

 acid, with the formation of one molecule of stearic acid as follows: 



H H „ H H 



CH3(CH2)7C:C(CH2)7C00H ^-*CH3(CH2)7C-C{CH2)7C00H 



H H 



Oleic acid Stearic acid 



When linoleic acid is used as the starting material, three products can 

 originate: 9-octadecenoic acid, 12-octadecenoic acid, or stearic acid: 



HHHH „ HHHH 



CH3(CH2)4C:C-CH2C:C(CH2)7C00H ^— *CH3(CH2U-C-CH2C:C(CH2)7C00H 



H H 



Linoleic acid 9-Octadecenoic acid 



HHHH HHHH 



CH3(CH2)4C:C-CH2G-C(CH2)7C00H ^-*CH3(CH2)4C-C-CH2C-C(CH2)7C00H 



H H HHHH 



12-Octadecenoic acid Stearic acid 



In the case of the reaction which results in the formation of stearic acid, 

 only one end product results, since it is completely symmetric and entirely 

 saturated. However, when linoleic acid is the starting point, the inter- 

 mediate products may be either cis or trans, so that at least four different 

 isooleic acids may result, namely cis- and frans-9-octadecenoic acids and 

 cis- and /rans-12-octadecenoic acids. It is quite obvious that the situation 

 becomes still more complicated when a triethenoid acid such as linolenic 

 acid is partially saturated. 



Variations in the end products produced on hydrogenation of di- or poly- 



619 C. Bosch, A. Mittasch, and C. Schneider, U. S. Patent No. 1,215,334 (Feb. 13, 1917). 



6M L. Kahlenberg and T. P. Pi, /. Phys. Chem., 28, 59-70 (1924). 



6" A. S. Richardson and A. O. Snoddy, Ind. Eng. Chem., IS, 570-571 (1926). 



622 E. B. Higgins, U. S. Patent No. 1,170,814 (Feb. 8, 1916). 



623 C. Paal, U. S. Patent No. 1,222,660 (Apr. 17, 1917). 



62< N. Sulzberger, U. S. Patent No. 1,338,709 (May 4, 1920). 



625 F. Goldschmidt, Seifenfabrik., 32, 713-720 (1912); Chem. Abst., 6, 2550-2551 

 (1912). 



