1885.] 



The Chemical Constitution of Isatin. 



205 



composition C 6 H 3 (N0 3 )(OH)COOC 2 H 5 (51-3 per cent. C and 4'37 

 per cent. H found; 51"2 per cent. C and 4*27 per cent. H, calculated). 

 The formation of a-nitrosalicylic acid from isato acid, as described 

 above, is easily explained upon the supposition that the anthranilic 

 acid (amidobenzoic acid) generated from the latter is nitrated by the 

 nitrous acid, and that in this nascent nitro-amidobenzoic acid the 

 amide is replaced by hydroxyl. 



C 6 H 3 (N0 2 )(NH 2 )COOH + NOOH=N 2 + H 2 + C 6 H 3 (N0 2 )(OH)COOH 



Nitro-amidobenzoic acid. Nitro-salicylic acid. 



The foregoing research explains the behaviour of isatoic acid sub- 

 stantially only in one direction. Other experiments are now being 

 made, by means of which the changes induced in this compound by 

 suitable oxidising and reducing agents are to be made clear, in order 

 thereby to gain new foundations for the right perception of the 

 chemical constitution of isatin and compounds derived from it. 



We possess in the substance obtained by the oxidation of indigo, and 

 named by me isatoic acid, a nitrogen compound which seems to be specially 

 fitted to shed light upon the question whether nitrogen can act not only as 

 a di-, tri-, tetra-, and penta-valent element (as in nitric oxide, ammonia, 

 nitrous acid, and nitric acid) , but also as a monovalent one. The mode of 

 formation and the chemical behaviour of this isatoic acid gain — through 

 the conception that it is benzoylcarboxylic acid, in which one of the five 

 phenyl hydrogen atoms is replaced by an atom of monovalent nitrogen, 

 and through the further supposition that isatin is its corresponding alde- 

 hyde — such a simple and, from all points of view, satisfactory explana- 

 tion, that only one already prejudiced by the idea that nitrogen can only be 

 trivalent can feel himself satisfied by ~the supposition that the molecular 

 weight of isatoic acid must be doubled, i.e., that it is a dibasic acid. None 

 of the facts which up till now I have discovered support this hypothesis ; 

 on the contrary, by the supposition that isato acid contains 1 atom of 

 monovalent nitrogen as substitute for 1 atom of hydrogen, they all obtain 

 the simplest and least strained explanation in such a degree that, in the 

 publication of my research on isatin and isatoic acid and their derivatives, 

 I have not discussed the question ivhether the nitrogen in them may 

 possibly be polyvalent. 



N.B. — Benzoyl carboxylic acid is usually termed phenyl glyoxylic 

 acid, so that nitrogen-benzoyl carboxylic acid = nitrogen- phenyl 

 glyoxylic acid. 



