1 86 REPORTS OF* INVESTIGATIONS AND PROJECTS, 



(NaOC,H,),CCeH,COO ^ (NaOC.HJ (0:C,H,:)CCeH,COONa ^ 

 A. Colorless. B. Somewhat colored. 



(NaOCeHJ (OiC.H.OCC^H.COONa 

 C. Deeply colored. 



[(CH3),NCeHj[Cl(CH3),N:C,H,:]CC,H,N(CH3),^ 

 B. Somewhat colored. 



[(CH3),NC,HJ[C1(CH3),N:C,H,:]CC,H,N(CH3), 



C. Deeply colored. 



We have found that the theory of tautomeric salts is entirely adequate to 

 make clear the constitution of the colored and colorless salts as well as the 

 formation of isomeric esters in the alkylation reactions of the acids and salts. 

 We have secured evidence which shows that in solutions of the salts of 

 phenolphthalein and analogous compounds at least three tautomeric salts, 

 A, B, and C, exist in equilibrium with each other and their ions. A is color- 

 less, B is somewhat colored, and C, an intra- or inter-molecular compound of 

 the quinone and phenolate groups which we call a quinone phcnolate com- 

 pound, is deeply colored. Each salt reacts with alkyl halides and forms the 

 corresponding colorless and colored esters, those corresponding to C probably 

 changing into those corresponding to B, and these sometimes changing into 

 those of the form A. Likewise the salts of rosaniline, and similar compounds, 

 exist in solution in the two tautomeric forms B and C. C, which we call a 

 quinaminone, is far more deeply colored than A. Colorless salts of the 

 phenolphthalein series corresponding to A are known in the salts of para- 

 oxydiphenylphthalid, the phenol methyl ester of phenolphthalein, the phenol 

 ethyl ester of tetrabromphenolphthalein, the anilides of phenolphthalein and 

 hydroquinonephthalein, etc. These yield with alkyl halides only the phenol 

 esters, as is to be expected. But the colored salt of the phenol ethyl ester 

 of fluorescein, which becomes in solution a mixture of the three salts cor- 

 responding to E and F and the quinone phenolate formed by the union of 

 these, yields with alkjd halides a mixture of the corresponding colorless and 

 colored phenol and carboxyl esters. 



(CH30CeH,)(NaOC,H,)CC,H,COO JJ(CH30C,H,)(0:C,H,:)CC,H,C00Na 

 E. Colorless. F. Somewhat colored. 



The chief source of color in dyestuffs (both basic and acid) is not the 

 quinone group, but one or more inter- or intra-molecular reversible combina- 



