Tautomerism of hydroxypyridines (I): The structure of 2,4‐dihydroxypyridine

Abstract

Syntheses of 2‐hydroxy‐4‐methoxypyridine, 4‐hydroxy‐2‐methoxypyridine, 4‐methoxy‐N‐methylpyridone‐2, and 2‐methoxy‐N‐methylpyridone‐4 are described.The ultraviolet absorption spectra of 50% aqueous ethanolic solutions of the above‐mentioned compounds and of 2,4‐dihydroxypyridine and 2,4‐di‐methoxypyridine are measured. Comparison of these spectra enables the determination of the predominant tautomeric structures of 2,4‐dihydroxypyridine and its derivatives.It appears that the chief structure of 2,4‐dihydroxypyridine in aqueous ethanol is that of 4‐hydroxypyridone‐2.Finally it is shown that the methyl derivative of 2,4‐dihydroxypyridine, obtained by Maquenne and Philippe a. L. Maquenne and L. Philippe, Compt. rend. 183, 506 (1904). b. Recently E. C. Taylor Jr., Aldo J. Crovetti, and Harvey M. Loux described an analogous synthesis of this substance from an isomer of ricinine ( J. Am. Chem. Soc. 77, 5445 (1955)). ) when heating ricinine with hydrochloric acid solution or by conversion of 4‐methoxy‐N‐methylpyridone‐2 with the same reagent according to Späth and Tschelnitz E. Späth and E. Tschelnitz, Monatsh. 42, 251 (1921). ), is 4‐hydroxy‐N‐methylpyridone‐2.