324 CHEMICAL DISCOVEKY AND INVENTION 



in the choice of the process adopted. The question is which of 

 the hydrocarbons present in coal-tar is to be chosen as the start- 

 ing point, supposing the operations leading to the dye being 

 about equally suitable ? This can only be answered by calcu- 

 lating the probable demand for the synthetic product, and 

 ascertaining the probable amount of the requisite coal-tar hydro- 

 carbon available. These considerations it was, which, according 

 to Dr. H. Brunck, director of the great colour works at Ludwigs- 

 hafen, led to the abandonment of the otherwise successful 

 process which depended on toluene, in favour of a process which 

 starts from the far more abundant naphthalene obtained from 

 coal-tar. 



The raw material of one of the modern processes is then 

 naphthalene, and the successive steps can be most concisely 

 indicated by the following formulae. 



Naphthalene heated with fuming sulphuric acid and a small 

 quantity of mercury is oxidised into phthalic acid. The sulphuric 

 acid is reduced to sulphur dioxide which, by the modern contact 

 process, is converted back again into sulphuric acid. It is there- 

 fore the oxygen of the air which thus indirectly acts on the 

 naphthalene. 



Naphthalene Phthalic acid 



C 10 H 8 gives C 6 H 4 (C0 2 H) 2 



Phthalic acid when heated (sublimed) loses water and is con- 

 verted into 



Phthalic anhydride 







By heating this substance in presence of ammonia it is con- 

 verted into 



Phthalimide 







This compound under the simultaneous action of alkalis and 

 chlorine in the form of alkaline hypochlorite yields 



Anthranilic acid 



