go Biological Chemistry. 



really the case, the following should be the formulae assign- 

 able to the chlorine substitution products of acetic acid : 



CH 2 C1 C0 2 H .... Monochloracetic acid. 

 CHC1 2 -C0 2 H .... Dichloracetic acid. 

 CC1 3 -C0 2 H ..... Trichloracetic acid. 



If, now, the carboxyl group has remained intact throughout 

 these operations, these substitution products should still 

 have a hydrogen replaceable by a metal and give salts with 

 the formulae CH 2 C1 - C0 2 M, CHC1 2 C0 2 M, CC1 3 - C0 2 1/ 

 (when M = Na, K, or any univalent metal). The hydroxyl 

 group should, furthermore, be replaceable by chlorine, and 

 it should be possible to obtain substances of the formulae 

 CH 2 C1-COC1, CHOla-COCl, CC1 3 -COC1, on treatment of the 

 above chlorine derivatives with phosphorus pentachloride. 

 As a matter of fact, all these reactions can be accomplished. 

 There seems, therefore, no other possible constitutional 

 formula for acetic acid than that which has been proposed, 

 which may be expanded into the following : 



H 

 H 



This indicates the presence of a methyl group and a 

 hydroxyl group, and the oxygen atom other than that in 

 the carboxyl group is directly united to a carbon atom as 

 it is in the aldehyde from which the acid is derived by 

 oxidation. 



The following are some of the chief fatty acids, with 

 their physical properties : 



Melting Boiling 



point. point. 



Formic acid H-C0 2 H 8-3 101 



Acetic CH 3 C0 2 H 16'5 118 



Propionic 8 H 6 -C0 8 H 36 141 



