Structure of Simpler Organic Compounds. 87 



Part VI. The Fatty Acids. 



On the oxidation of aldehydes with suitable oxidizing 

 reagents a series of products, to which reference has been 

 repeatedly made, is formed. These form the important 

 class of organic compounds known as the fatty acids, 

 as the higher members of the series are obtained from the 

 natural fats. Formic aldehyde and acetic aldehyde yield 

 in this way the two lowest members of the series, namely, 

 formic and acetic acid, H-C0 2 H and CH 3 -C0 2 H. 



The general formula assigned to these substances is 



',>: R 



Formic and acetic acids would consequently have the 

 formulae 



They all contain the group ^\QH' w *^ cn * s known as 



the carboxyl group, and is characteristic of most of the 

 organic acids. Substances containing such a group (except 

 those which contain also a basic or alkaline group as, for 

 example, certain ammo-acids, see p. 219) have definite 

 acidic properties. Their solutions turn red litmus paper 

 blue, and they can be neutralized by alkalis and other 

 bases, and give rise to a well-defined series of salts. Thus, 

 with sodium hydroxide 



E-COja + NaOH = R-C0 2 Na + H a O 



This fact alone might indicate the presence of a hydroxyl 

 group such as exists in the alcohols. There is, however, a 

 marked difference between the action of alkali metals in 

 the case of the alcohols and acids ; for whereas the metallic 



