Chlorine atoms a to the nitrogen displace the tautomeric equilibrium of pyridones significantly in favour of the hydroxypyridine form, whereas chlorine atoms in other positions have much less effect. a-Monochloropyridones are shown to exist to an increasing extent in the hydroxypyridine form as the dielectric constant of the medium decreases.RELATIVELY little is known of the effect of ring substituents on the tautomerism of simple pyridones. Although a 3-nitro-group has little apparent effect on the tautomeric equilibrium of 4-~yridone,~ we recently disclosed the large effect of a 6-hydroxy-or 6-methoxysubstituent on the tautomerism of 2-pyrid0ne.~ This prompted us to investigate the general effect of substituents on the pyridone-hydroxypyridine equilibrium. We chose chloro-substituted compounds for an initial study because a reasonably representative selection was available. den Hertog et aZ.4 first prepared 2,3,5,6tetrachloro-4-hydroxypyridine, but gave no indication as to its tautomeric structure. 3,4,5,6-Tetrachloro-2hydroxypyridine has previously been reported on several occasions 5-7 and the ultraviolet spectrum in methanol differs from that of the N-methyl analogue, indicating that the hydroxy-tautomer is favoured. The preparation has been reported of 6-chlor0-2-hydroxypyridine,* and 2-chlor0-,~ and 2,6-dichlor0-4-hydroxypyridine,~~ but no evidence is offered as to the structure.Two groups 11, l2 recently concluded from infrared and ultraviolet spectra that 2 , 3,5,6-te t rafluoro-4-hydroxypyridine exists almost completely in the hydroxy-form.Preparation of Comj5ounds.-2-Chloro-4-pyridone was prepared from 2-chlor0-4-nitropyridine.~ 2,6-Dichloropyridine afforded 6-chloro-l-methyl-2-pyridone by successive quaternisation and hydrolysis. Further Nmethylpyridones were prepared from the parent pyridone and methyl iodide and methoxypyridines from the corresponding chloro-compounds and methoxide ions.Attempts to prepare l-methyl-2,6-di-and l-methyl-2,3,5,6-tetra-chloro-4-pyridone failed ; only the methoxy-isomers were obtained by the methyl iodide method, and the attempted deamination by diazotisation of 4-amino-2,6-dichloro-l-methylpyridinium perchlorate f ailed.13 EXPERIMENTAL 6-Chloro-2-hydroxypyridine (Aldrich), m. p. 126-127" (from aqueous ethanol) (lit.,* 128-129") ; 6-chloro-2-meth-* B. p. not previously reported. This structure was confirmed 1 Part VIII, A. R. Katritzky and B. Ternai, J . Chem. SOC. ( B ) , Personal communication from Dr.

Glutaconimide is shown to exist to the extent of some 66% as 6-hydroxy-2-pyridone. The tautornerism of the anionic and cationic forms has been elucidated together with that of the 0-and N-methyl derivatives.

Katritzky, Kucharskn, and Rowe 3093 * The determination was done by potentiometric titration using an E.I.L. model 23A directreading pH meter. Other results were obtained on a Unicam S.P. 500 spectrophotometer with 0 . 1 ~potassium dihydrogen phosphate-dipotassium hydrogen phosphate buffer for proton addition t o 2-phenacylpyridine, and in standard sodium hydroxide for the other compounds.predominates in aqueous solution for all the potentially tautomeric compounds, and that the KT are 220,2,000,000, and 450 for the 2-, 3-, and 4-series, respectively. The phenacylpyridines are all somewhat weaker as bases than pyridine (pK, = 5-21>, reflecting the l

A general method for the evaluation of the kinetics of the solution phase bromination of alkanes and substituted alkanes is presented. The model used considers reversible transfer reactions of the radicals formed with both hydrogen bromide and hydrogen tribromide. Cage reversal of the geminate radical – hydrogen bromide pair and reversal with hydrogen tribromide are used to rationalize the differences observed between the vapor and solution phase kinetics.The method is applied to the bromination of 1-chlorobutane.

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