98 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Propionic Acid. CH 3 . CH 2 . COOH. 



Propionic acid is present with acetic acid in pyroligneous acid; it is 

 found in sweat and is a product of putrefactive fermentation. It is most 

 easily prepared by the oxidation of propyl alcohol with potassium bichromate 

 and sulphuric acid. 



Propionic acid closely resembles acetic acid in its properties : it is a liquid 

 which boils at 140 and has asp.gr. of -996^1 19. It mixes with water 

 in all proportions, and may be separated from solution by adding calcium 

 chloride, which causes it to float as an oily layer. 



Butyric Acid. CH 8 . CH 2 . CH 2 . COOH. 



Butyric acid occurs in the free state in various animal and vegetable 

 secretions in the form of its glyceride butyrin ; it is always stated to exist 

 in but er to the extent of about 6 per cent., but this compound could not be 

 separated by Hurtl-jy by the distillation of pure butter in vacuo. Since butyric 

 acid resu'ts Irom the putrefaction of proteins and amino acids, it seems most 

 piobable that its occurrence in butter is due to the presence of butter milk 

 which has not been removed and which has undergone decomposition. Its 

 smell is always obvious in rancid butter. 



Butyric acid is prepaied by the butyric fermentation of glucose and 

 other carbohydrates in the same way as lactic acid (p. no). The filtered 

 solution is evaporated, acidified and distilled. 



Butyric acid is a colourless liquid with a pungent and disagreeable smell. 

 Like propionic acid it can be separated from aqueous solution by the addition 

 of calcium chloride. 



v 

 Isobutyric Acid. >CH . COOH. 



CH/ 



Isobutyric acid is found as the free acid, or as ester, in certain p'ants. It is 

 a product of putrefaction of proteins and would arise from the amino acid, vaiine. 

 It is very like normal butyric acid, but not so offensive in smell. 



Valerianic or Valeric Acids. C 4 H 10 . COOH. 



Four isomers are possible. The commom valerianic acid is isovaleric 



acid /CH . CH 2 . COOH which occurs in valerian root and various 



other animal and vegetable secretions. It is probably formed by the decom- 

 position of leucine. 



CH, 

 Methyl ethyl acetic acid /CH . COOH is also found in nature. 



This compound is optically active and would be derived from isoleucine by 

 putrefaction. 



Normal valerianic acid, whi( h has been found as a fermentation product, 

 presumably of carbohydrate, mo c t likely arises from amino acids in the same 

 way as the other acids. 



These acids are liquids with an unpleasant smell and behave in most 

 respects like butyric acid. 



Caproic to Myristic Acids. 



Tin: fatty ai ids with 6, 8 and 10 carbon atoms are found in combination 

 in various fats. They ;ire liquids slightly soluble in water. 



The tatty acids with 12 and 14 atoms of carbon are solids of low melting- 

 point, 



