38 THE ROYAL SOCIETY OF CANADA 



ammonium salt of diketohydrindylidene-diketohydrindamine. The 

 primary action of ammonia on hydrindantin to form diketohydrin- 

 dylidene-diketohydrindamine, involves the replacement of a hydroxyl 

 group and an ethereal oxygen atom by a nitrogen atom with the loss 

 of two molecules of water — a reaction, as far as we are aware, without 

 parallel in organic chemistry. We believe it much more likely that 

 the succeeding stage in the reaction is the action of ammonia on the 

 diketohydrindol to give diketohydrindamine 



» 

 C6H4 - CO C6H4 - CO 



I I + NH3 =1 I + H20 



CO CHOH CO CHNH2 



This compound, according to Ruhemann, readily oxidises to the 

 analogue of murexide, readily condenses with aldehydes, and conse- 

 quently would be expected to condense with triketohydrindene 

 hydrate to give diketohydrindylidene-diketohydrindamine, 



C6H4-CO CO-C6H4 



I I + 11= H2O + 



CO CH ■ NH2 CO— CO 



C6H4 - CO CO - C6H4 



CO CH-N = C CO 



of which the ammonium salt is the required blue coloration. 



In this way a satisfactory idea can be gained of the mechanism 

 of the "ninhydrin" reaction with amino acids. To apply it, however, 

 as such, to the reaction with ammonium salts is impossible, for am- 

 monium chloride, nitrate, and sulphate, are not, in any sense of the 

 term, reducing agents. It is to be noted that ammonium salts do not 

 react in very dilute solution but all react in presence of pyridine to 

 give a constant amount of decomposition independent of the acid 

 radicle in the salt. All reduction must thus come from the triketo- 

 hydrindene hydrate itself. In presence of pyridine the triketone 

 in part hydrolyses to give the yellow colored phenylglyoxal carboxylic 

 acid 



C6H4 — CO C6H4 — COOH 



I I 4- H2O = I 

 CO CO CO CHO 



