130 II. CHEMISTRY OF FATTY ACIDS AND GLYCEROL 



bromo-''*^; phenylsemioxamazide^"; and /3-naphthylhydrazine.^^^ 



One important group of reactions of the aldehydes can be considered as 

 polymerizations. Practically all aldehydes will undergo such a change 

 even if kept at room temperature. Valeraldehyde spontaneously changes 

 to a poljoner melting at 83-84°C. in ether solution in the presence of potas- 

 sium carbonate, while heptanal undergoes a similar reaction to produce a 

 product melting at 51-52°C.^^^ As indicated earlier, the polymers which 

 are formed are less reactive; in fact, the polymer formation frequently 

 must be considered as a competitive reaction of the aldehydes. This re- 

 moves these components from the field of activity by changing them to 

 relatively stable polymers. 



One condensation which is of especial interest biologically is the so-called 

 aldol condensation. When aldehydes are heated in the presence of a cat- 

 alyst, two molecules combine to a hydroxy-aldehyde. In the case of 

 acetaldehyde, the reaction proceeds as follows: 



/H /H /H 



2CH3C=0 3-CH3C-CH2-C=0 



Acetaldehyde Aldol 



It has been suggested that, in the animal body, the alcohol is reduced and a 

 new condensation of acetaldehyde results. By a series of such condensa- 

 tions and reductions of the alcoholic groups, a long-chain aldehyde is built 

 up which is eventually oxidized to a fatty acid. This has been suggested 

 as a logical method for the biological synthesis of fat from a carbohydrate 

 intermediate, acetaldehyde.^^" 



The higher aldehydes such as caprylaldehyde likewise undergo the aldol 

 condensation reaction to produce branched-chain alcoholic aldehydes 

 which may be converted to unsaturated aldehydes by magnesium as fol- 

 lows:*" 



/H „ /H/CeHis/H -h^o /^ /^ 



2CHj(CH2)6C=0 ^- *CH3(CH2)6C-CH-C=0 ^CHjlCHjlsC-C C=0 



^OH CsHis 



Octanal 2-Hexyl-3-hydroxydecanal 2-Hexyl-2-decenal 



«« C. -H. Kao, T. -K. Tao, C. -H. Kao, and P. P. T. Sah, /. Chinese Chem. Soc, 4, 

 69-74 (1936). 



«' P. P. T. Sah and W. -P. Han, Science Repts. Nat. Tsing Hua Univ., AS, 469-476 

 (1936); Chem. Abst, SI, 3825 (1937). 



«8 H. -M. Chen and P. P. T. Sah, /. Chinese Chem. Sue, 4, 62-68 (1936). 



«9 G. Bruylants, Ber., 8, 414-416 (1875). 



*^ A. Magnus-L6vy (1894), cited by G. Lusk, Elements of the Science of Nutrition. 

 4th ed., 1928, p. 350,' 396. 



«' P. Shorigin, W. Is.saguljanz, and A. Gussevva, Ber., B66, 1431-1435 (1933). 



