686 Professor H. E. Boscoe [May 27, 



Following up this view, Claissen and Shadwell, two of Kekule's 

 pupils, succeeded in preparing isatin, and, therefore, now indigo, from 

 ortho-nitro-benzoic acid. 



The following are the steps in the ascent : — 



1. Ortho-nitro-benzoic acid acted on by phosphorus pentachloride 



yields the chloride 06H4(N02)C0C1. 



2. This latter heated with silver cyanide yields the nitril CqH^ 



(N02)C0.CN. ^ 



3. On heating this with caustic potash it yields ortho-nitro-phenyl- 



glyoxylic acid, C6H4(N02)CO.C02H. 



4. This is converted by nascent hydrogen into the amido-com- 



pound C6H4(NH2)C0.C02H. 

 6. And this loses water and yields isatin, CgH^NH . CO . CO. 



(Q. E. D.) 



The reasons why this process will not work on a large scale are 

 patent to all those who have had even bowing acquaintance with such 

 unpleasant and costly bodies as phosphorus pentachloride or cyanogen. 



Process No. 2. — Baeyer's (1878) synthesis from ortho-nitro-phenyl 

 acetic acid. 



This acid can be obtained synthetically from toluol, and it is first 

 converted into the amido-acid, and which, like several ortho-compounds, 

 loses water, and is converted into a body called oxindol, from which 

 isatin, and therefore indigo, can be obtained. The precise steps to be 

 followed are : — 



This again with nascent hydrogen gives amidoxindol 

 CH(NH2) 



