Structure of Simpler Organic Compounds. 105 



Part IX. The Dibasic Acids. 



A large number of organic acids are known which 

 contain more than one carboxyl group (see p. 87). As 

 each of such groups contains a hydrogen replaceable by a 

 metal, these acids will be poly basic ; those containing two 

 carboxyl groups will have two hydrogens replaceable, and 

 are therefore dibasic; those containing three carboxyl 

 groups are tribasic; and those with still more carboxyl 

 groups will have still higher basicities. 



The simplest dibasic acid is oxalic acid, which can be 

 represented by the formula 



COOH 



COOH 



that is, it is a substance consisting of two carboxylic 

 groups only. 



The formula of this substance, which is found in a large 

 number of plants, is readily demonstrated by two methods 

 of synthesis. In the first place, it can be obtained from 

 cyanogen by hydrolysis ; if an aqueous solution of this 

 gas is kept for some time it forms, amongst other products, 

 ammonium oxalate 



CN COONH, 



| +4H.O= | 



CN COONH 4 



It will be remembered that the (CN) nitrile group always 

 undergoes hydrolysis according to the equation 

 CN + 2H 2 = COOH + NH 3 



(In the absence of a mineral acid the ammonia will 

 form an ammonium salt with the carboxylic acid thus 

 produced, as in the above equation representing the decom- 

 ition of cyanogen.) 

 The second synthesis is an example of the oxidation 



