viii, a, 8 Pratt and Gibbs: Two Phthaloximes 175 



upon the structure of the oximes. The absorption spectra of 

 the indandions have been carefully studied by Hantzsch, and 

 found to vary in a marked degree with change of solvent. Phenyl 

 indandion was shown to give only general absorption in ether 

 solution, but selective absorption in methyl alcohol with 1 well- 

 developed band and 2 step-offs. In the presence of alkali these 

 develop into 3 well-marked absorption bands. The equilibrium 

 of the enol-keto tautomerism in ether solution differs from that 

 in methyl alcohol, and causes a corresponding difference in the 

 absorption spectra. 19 



The application of Hantzsch's work to our problem gives ad- 

 ditional evidence concerning the structure of phthaloxime. If 

 the oxime were correctly represented by the symmetrical for- 

 mula, it might be expected to resemble the indandions both chem- 

 ically and spectroscopically, and undergo enol-keto tautomerisrm 

 The absorption spectra would show this equilibrium, and the ap- 

 proximate amount of the enol form in solution could be deter- 

 mined by titration with bromine. 20 Molecular rearrangement 

 of this type would result in the following equilibrium: 



yC=0 ,0- OH(M) 



C 6 H 4 ^NOH *± C 6 H 4 y^O 



\c=o \c=o 



Solutions of phthaloxime do not react with aqueous bromine, 

 however, and no chemical or optical indications of enol-keto 

 tautomerism could be observed. Moreover, the absorption spec- 

 tra of the oximes in various neutral solvents are practically iden- 

 tical, do not show evidences of an enol-keto band, and are of an 

 entirely different type from those given by the indandions. The 

 other alternative for salt formation with a symmetrical oxime 

 would be direct replacement of hydrogen by a metal atom, giving 

 salts analogous in many respects to the salts of phthalimide. 

 Since neither of the above conditions is characteristic of phthal- 

 oxime, it seems very probable from spectroscopic evidence alone 

 that only the unsymmetrical structure will explain the facts. 



Oximido-oxazolone is colorless or faintly yellow, and also 

 forms highly colored salts with colorless metals. Hantzsch Z1 



19 Hantzsch, loc. cit. 



"Meyer, Ann. d. Chem. (Liebig) (1911), 380, 212. 



^ Ber. d. deutschen Chem. Ges. (1909), 42, 1007; (1910), 43, 68. 



