124 li. CHEMISTRY OF FATTY AClDS AND GLYCEROL 



(a) Fatty Acid Aldehydes. There is much evidence that the fatty acid 

 aldehydes are normal metabolic products. Feulgen and his collabora- 

 ^QPg4i8-422 carried out the classical work in proving the presence and wide- 

 spread distribution of the fatty acid aldehydes in tissues. Their results 

 have been confirmed by Anchel and Waelsch,^^^ who isolated 0.05 to 0.2% 

 of aldehydes (mostly Cie and Cis) from the brain and muscle of rats and 

 cattle. The importance of these aldehydes is further emphasized by the 

 fact that they are likewise found in the plant kingdom, where they have 

 been prepared from a number of the plant oils. The Cs and Cg aldehydes, 

 octanal (CH3(CH2)6CHO) and nonanal (CH3(CH2)7CHO), are quite 

 general components of essential oils. Decanal (CH3(CH2)8CHO) has 

 been reported in significant amounts in coriander oil,^^^-'*^^ while dodecanal 

 (CH3(CH2)ioCHO) has been isolated from the oil of the lily of the valley, ^^e 

 Marcelet'*" prepared an aldehyde-alcohol with 18 carbons from olive pulp. 

 Many of the floral odors are to be traced to the shorter chained aldehydes, 

 each one of which possesses a characteristic aroma. Violet leaf oil has 

 been found to contain a doubly unsaturated aldehyde, ^^^ i.e., 2,6-nonadi- 

 enal, which has the formula, CH3CH2CH :CHCH2CH2CH :CHCHO. Since 

 it would appear that aldehydes play an important role as intermediates in 

 fat oxidation and as primary tissue components in the animal, as well as 

 being essential products in the vegetable kingdom, a fairly complete dis- 

 cussion of their chemistry would seem to be desirable. 



a'. Methods of Preparation of Aldehydes: One Avidely used method 

 for preparing aldehydes involves the controlled oxidation of the corre- 

 sponding alcohols. When a mixture of alcohol vapor and a limited amount 

 of air is passed over a silver catalyst'*^^ at 230-300°C'., the aldehydes are 

 formed. Yields as high as 96% have been reported for octanal (from 

 caprylic alcohol)^'" and 82% for the higher aldehydes obtained by this 

 procedure. Metallic nickel (5%) can be used as a catalyst in liquid-phase 

 dehydrogenation at a carefully regulated temperature ; 20% of the theoret- 



"8 R. Feulgen and K. Voit, Arch. ges. Physiol. Pfliigers, 206, 390-410 (1924). 



^" R. Feulgen, K. Imhauser, and M. Behrens, Z. physiol Chcm., 180, 161-179 (1929). 



"s" R. Feulgen and M. Behrens, Z. physiol. Chem., 256, 15-20 (1938). 



^21 R. Feulgen and T. Bersin, Z. physiol. Chem., 260, 217-245 (1939). 



«2 M. Behrens, Z. physiol. Chem., 191, 183-186 (1930). 



«3 M. Anchel and H. Waelsch, J. Biol. Chem., 145, 605-613 (1942). 



'2^ P. P. Shorygin and V. P. Osipova, Sintezy Dushistykh Veshcheslv, Sbomik Statei, 

 246-247 (1939); Chem. AbsL, 36, 3781 (1942). 



"5 L. Y. Bryusova, R. Y. Shagalova, and N. Novikova, Sintezy Dushistykh Veshcheslv, 

 Sbomik Statei, 247-252 (1939); Chem. AbsL, 36, 3781 (1942). 



^26 W. Hannemann, Deut. Parfum.-Ztg., 9, No. 8/9, 7 (Api"- 15, 1923); Chimie & Indus- 

 trie, 11,941 (1924). 



«7 H. Marcelet, Cornpt. rend., 206, 529-530 (1938). 



<28 E. Spath and F. Kesztler, Ber., B67, 1496-1500 (1934). 



*29 C. Moui-eu and G. Mignonac, Compt. rend., 170, 258-261 (1920). 



"» Z. P. Aleksandrova, /. Applied Chem. U S. S. R., 10, 105-115 (1937); Chem. Abst., 

 31, 4266 (1937). 



