1 1 2 Biological Chemistry. 



From this ester the free acid can be obtained by 

 hydrolysis, namely : 



/COOH 



CRR' 



\X)OH 



which on heating above its melting point decomposes 



=C0 2 4-CRR'-CO-OH 

 \X).OH 



yielding a dialkyl substitution product of acetic acid. 

 The value of this process for the determination of the 

 constitution of fatty acids is evident. To take only one 

 concrete example : 



If sodio ethyl malonate is treated with ethyl iodide, 

 and the ester thus produced is hydrolyzed, and the acid so 

 obtained heated above its melting point, the final product, 

 as already mentioned, is CH 2 (C 2 H 5 )CO OH that is, normal 

 butyric acid. If the sodio-malonic ester is, however, 

 treated with methyl iodide, and the methyl derivative of 

 malonic ester thus produced is treated with sodium ethoxide, 

 and the sodium salt is then treated with methyl iodide, 

 the dimethyl-malonic ester is obtained ; the free acid of 

 this ester, on heating above its melting point, yields 

 CH(CH 3 ) 2 COOH, dimethyl-acetic or ^sobutyric acid, 

 which is isomeric with ethyl-acetic or normal butyric 

 acid. Reference has already been made to the fact that 

 it is possible by synthetical methods to distinguish between 

 the various fatty acids. These two acids will themselves 

 differ in their properties, as will those of their salts, and 

 they can be readily distinguished by ascertaining these 

 properties. This process has been dwelt upon in some 

 detail, as it is a synthetical method of very wide applica- 

 tion. It is possible, for example, that a fatty acid of the 



