THE ABSORPTION SPECTRA OF PHENOQUINONE, 2,5-DIANI- 



L1NOQUINONE, 2,5-DIANILINOQUINONEANIL, AND 



2,5-DIANILINOQUINONEDIANIL 



(AZOPHENINE) 



By D. S. Pratt and H. D. Gibbs 1 



{From the Laboratory of Organic Chemistry, Bureau of Science, 

 Manila, P. I.) 



Two text figures 



In the study of the compounds which cause the red color of 

 phenol 2 it was pointed out that the coloration is due to the 

 oxidation of phenol to quinone with the subsequent condensation 

 to phenoquinone, although physico-chemical methods would be 

 necessary to prove the presence of the latter compound. The 

 most satisfactory method appeared to be based upon the absorp- 

 tion spectra of the compounds in question. 



Phenoquinone, crystallized from ligroine, was dissolved in ab- 

 solute alcohol, and the absorption spectrum photographed in the 

 manner described in our previous work. 3 The absorption curves, 

 plotted with logarithms of the dilutions and oscillation frequen- 

 cies, are shown in fig. 1, and the curves of quinone and 'phenol 

 in alcohol are included for purposes of comparison. 



In alcohol, the color band shows in one-tenth molar solution 

 and closely resembles that of quinone. Dilutions of this solu- 

 tion to hundredth and thousandth molar concentrations give 

 curves that are not continuations of the tenth molar and of each 

 other. This discontinuity upon dilution is not shown by quinone 

 and phenol, and since these compounds follow Beer's law it is 

 evident that dilutions of phenoquinone solutions do not give the 

 expected concentrations of phenoquinone. This is due to disso- 

 ciation which may be expressed by the equilibrium equation: 



C 6 H 4 2 +2C 6 H 5 OH ^ C 6 H 4 2 -2C 6 H 5 OH. 



In order to test the validity of this assumption, we have dis- 

 solved in alcohol quantities of quinone and phenol calculated for 

 tenth molar solution of phenoquinone and find that the absorp- 

 tion curve of this solution coincides with that obtained by dis- 



1 Associate professor of chemistry, University of the Philippines. 



' Gibbs, This Journal, Sec. A (1908), 3, 364. 



'This Journal, Sec. A (1912), 7, 371; (1913), 8, 33. 



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