THEORY OF THE PROCESS 379 



and nitrates are mixed, does not play at least a part in the re- 

 duction of the nitro into the amido compounds. 



329. Theory of the Process. The theory of the process by 

 which salicylic acid converts nitrates to ammonia is as follows: 



r. When salicylic acid and sulfuric acid are added to a nitrate, 

 the sulfuric acid takes up water and one of the hydrogen ele- 

 ments of the salicylic acid is replaced by NO 2 , forming nitro 

 salicylic acid. This reaction takes place without heat. It is 

 probably mononitro and not dinitro salicylic acid that is formed. 

 The reaction is probably as follows : 



(i) C 6 H S .OH.CO 2 H+HNO 8 +H,SO 4 = 

 C 6 H 4 (NO 2 ).OH.CO 2 H+H,SO 4 +H 2 O. 



2. Subsequently when zinc sulfid is added the hydrogen sulfid 

 liberated reduces the nitro salicylic acid to amido salicylic acid 

 as follows: 



(2) C 6 H 4 (N0 2 ).OH.C0 2 H+ 3 H 2 S4-H 2 S0 4 + 

 C c H 4 (NH 2 ).OH.CO 2 H+ 3 S+2H 2 O-f-H 2 SO 4 . 



3. The strong sulfuric acid and heat on the amido salicylic acid 

 breaks it up and there is formed ammonium sulfate, carbonic 

 acid, sulfur dioxid and water, as follows : 



(3) 2C 6 H 4 (NH 2 ).OH.CO 2 H+28H 2 SO 4 = 

 ( NH 4 ) 2 SO 4 + i4CO 2 +27SO,+32H,O. 



Similar reaction probably occurs when benzoic acid or phenol 

 is used, but either nitro compounds are not as readily formed or 

 they are not as easily converted into amido compounds, and pro- 

 bably the heat caused by the reaction when phenol is used is the 

 cause of the loss of some nitric acid. Furthermore, phenol and 

 benzoic acid do not break up as easily in the final reaction and, 

 therefore, it takes longer to complete the oxidation than when 

 salicylic acid is used. 



Other nitro- and amido-forming compounds might be sub- 

 stituted for salicylic acid, but by the use of salicylic acid, the 

 method is so simple and accurate that it is doubtful whether any 

 substance other than salicylic acid would improve the method. 



Other substances have been under observation, e> g., pure potas- 

 sium nitrate, using gallic acid in the place of salicylic acid, gave 



