Stability of N-heterocyclic oxime derivatives. Part IV. The kinetics of the sodium hydroxide-catalysed hydrolysis of phosphonylated ketoximes in water at 15, 20, 25, and 30°

Abstract

The decomposition of O-isopropyl methylphosphonylated and O-isopropyl ethylphosphonylated oximes of acetophenone, 2-, 3-, and 4-acetylpyridine, and 2-, 3-, and 4-acetylpyridinium iodide has been studied in alkaline solution. With the exceptions of the 2- and 3-acetylpyridinium compounds, the reactions proceed to give quantitative yields of the parent oximes. The 2-acetylpyridinium compound yields a mixture of the parent oxime and 1-methyl-2(1H)-pyridone. With the exception of the reaction of the 3-acetylpyridinium compounds which have not been fully elucidated, the reactions were found to be of the first order with respect to the phosphylated oxime and the hydroxyl ion, and the second-order rate constants have been determined at 15, 20, 25, and 30°. The reaction yielding the parent oximes obeys the Hammett equation, having a reaction constant of 0·624.

The activation parameters E_a(kcal./mole) and ΔS^‡(e.u.) have been determined and are for O-isopropyl methylphosphonylacetophenone oxime 10·2 and –32·4, for O-isopropyl ethylphosphonylacetophenone oxime 11·0 and –33·6, for O-isopropyl methylphosphonyl-2-, 3-, and 4-acetylpyridine oxime 9·9 and –31·7, 10·1 and –31·5, and 9·5 and –32·4, for O-isopropyl methylphosphonyl 4-acetylpyridinium oxime iodide 9·7 and –27·1, for O-isopropyl ethylphosphonyl-2-, 3-, and 4-acetylpyridine oxime 10·5 and –33·1, 10·7 and –33·1, and 10·6 and –32·3, and for O-isopropyl ethylphosphonyl-2- and 4-acetylpyridinium oxime iodide 10·1 and –27·7 and 9·9 and –30·0.