100 Journal of the Mitchell Society ^April 



— C— OH — C=0 



(A) II ^ 1 (B) 



— C— H — C=H2 



A represents the enol form and B the keto form. The first 

 type is a phenol or if in the aliphatic series an alcohol while the 

 second type is a ketone. ISTew cases of this sort have been 

 coming to light in recent years. It is clearing up some douhtful 

 questions of constitution.. For instance Meyer (Ann., 379,37 

 (1910)) has lately shown that anthranol is in reality anthrone, 

 the keto-form. As a rule when these isomeric forms are separate 

 and in the dry state they are stable but in solution they are 

 unstable and pass readily into each other. The reaction is re- 

 versible and incomplete. The direction of the reaction depends 

 upon the temperature and the nature of the catalysor. Since 

 both forms exist in the same solution, the solution will respond 

 to the reaction of the hydroxyl group and of the carbonyl group. 

 The relative amounts of the two forms in solution is difficult to 

 determine, since the equilibrium is very readily disturbed. A 

 number of methods have been employed. Meyer (Ann., 379,37 

 (1910), 396,141 (1912)) has proposed a titration method with 

 bromine at a low temperature. The enol-form, e. g., anthranol, 

 gives a strong blue fluorescent solution whereas the solution of 

 anthrone is non-fluorescent. Since bromine acts quickly upon 

 the enol-form and not upon the keto-form, the end point or dis- 

 appearance of the fluorescence is readily seen if the solution is 

 illuminated by ultraviolet light given by iron electrodes. This 

 method we were unable to use in our case though we made a 

 nu^mber of attempts to do so. We found that the action of 

 bromine upon the tetrahydroxynaphthalene was not smooth and 

 sufiiciently well defined. 



An alkaline solution of the yellow compound shows a strong 

 greenish fluorescence, indicating the presence of at least some 

 of the enol-form. The reaction with acetic anhydride, which 

 yields a tetracetyl derivative, also points to the enol-form but 

 Zincke and Schmidt give no indication of the yield obtained. 

 Reactions in strongly alkaline solutions applicable to the car- 

 bonyl group can not be made owing to the ready oxidation to 

 naphtazarine. For this reason w^e are employing phenylsemi- 



