270 The Ninhydrin Reaction [Jan. 



acids and realized its importance to biological chemistry. As a 

 result of his researches, Ruhemann showed that the reaction be- 

 tween triketohydrindene Hydrate and the amino acids depends upon 

 the presence of free, intact, amino and carboxyl groups which are 

 attached either to an ahphatic Compound (radical) or to the aH- 

 phatic side chain of an aromatic Compound. The amino group may 

 be either in the a, ß, y, 8 or e, position although the a-compounds are 

 the most reactive ; the other Compounds usually require the apphca- 

 tion of heat to produce a color. The formation of the color sub- 

 stance is associated with the production of an aldehyde. Tests with 

 a number of amino acids and other biological products^ have shown 

 that the blue reaction is given by Compounds having the groups indi- 

 cated above.^ 



It has been noted (Ruhemann) that a blue coloration results 

 when a Solution of triketohydrindene hydrate is warmed in strongly 

 alkaline Solutions ; upon dilution the color disappears, or with dilute 

 alkalies the reaction is obtained only with difficulty. Subsequently''' 

 it was shown that conc. Solutions of alcohols, aldehydes, ketones 

 and reducing sugars give the red or blue coloration when warmed 

 with triketohydrindene hydrate, which is intensified by the addition 

 of alkali. Dilution here, as with the alkalies, resulted in the dissipa- 

 tion of the color. The colored products obtained with these sub- 

 stances under the conditions outlined above, are not the same as 

 those formed with amino acids. 



of alcohoHc potassium hydroxid sol., gives a Substitution product — the hydrate 

 of 2:3-bis (/'-dimethylaminoanilo) a-hydrindone, 



CeH,— C:N-CeH,-N(CH3), 

 I I H2O 



CO — C:N-CÄN(CH,)a 



•which, when warmed slightly with dilute sulfuric acid, gives triketohydrindene 

 hydrate. 



5 Ruhemann: Loc. cit.; Abderhalden and Schmidt: Zeit. f. physiol. Cheni., 

 191 1, Ixxii, p. 37. 



• Ruhemann found that one part of triketohydrindene hydrate in 15,000 of 

 water gives a reaction with glycocol, while the same dilution gives a yellow col- 

 oration with ammonia — ordinarily, red to reddish yellow in more concentrated 

 Solutions. Abderhalden and Schmidt found that, when o.i gm. of the substance 

 is dissolved in 30 c.c. of water and O.i c.c. of this is taken, glycocol gives a dis- 

 tinct reaction in dilutions of i : 10,000, alanin a sharp reaction at i : 10,000 and 

 /-tyrosin at i : 5,000. 



^ Halle, Loewenstein and Pribram : Biochem. Zeit., 1913, Iv, p. 357- 



