lOlSl ISOMEEISM OF THE HyDROJUGLONS 189 



order to isomerize it. One needs only to heat ii-ntil it melts in 

 order to obtain an equilibrium out of which one can readily 

 isolate nearly three-fourths as the /8-componnd. In order to 

 convert this into the a-form it is sufficient to dissolve it in alkali 

 with the exclusio'n of air and then to acidify. This is not a case 

 of the wandering of an hydroxyl group but rather a case of 

 keto-enol isomerism. 



a-Hydrojuglone is a true trihydroxynaphthalene (1, 4, 8). 

 Its solutions are distinguished by a very strong fluorescence. 

 /S-Hydrojuglone is the keto form of it in which one of the two 

 hydroxyl groups in the para positions has experienced a trans- 

 formation into a carbonyl group, according to one of the follow- 

 ing formulas : 



OH 



OH O 



H 

 H 



H OH OH 



We are able to support this view since we have obtained 

 well crystallized semicarbazones of /?-hydrojuglone with semi- 

 carbazine and with phenylsemicarbazine while analogous deri- 

 vatives of a-hydrojuglone could not be obtained. An oxime of 

 jS-hydrojuglone was also observed but a closer study of it has 

 not been undertaken. That the two isomers yield the same 

 triacetyl and tribenzoyl derivatives is in agreement with this 

 conception. But it does not well explain the behavior of these 

 derivatives on hydrolysis. The acetyl compounds yield y8-hydro- 

 juglone by the action of strong sulfuric acid, while a-hydrojug- 

 olne according to Mylius is not transformed into its isomer by 

 sulfuric acid. 



The isomerism of the hydro juglones is the first case if keto- 

 enol isomerism of a phenol in the naphthalene series. It ranges 

 itself alongside the desmotropic phenomena of the meso-phenols 

 of the anthracene series (dianthranol, anthranol and anthra- 

 hydroquinone) which Hans Meyer^ and especially Kurt H. 

 Meyer'* have described in their important investigations. 



^Ber. der deutsch. chem. GeseU., 42,143 (1909) ; Monatsh., 30,165 (1909). 

 *Ann., 379,37 (1910-'ll) ; Meyer and Sander, Ann., 396,133 (1913). 



