The Kinetic Studies of the Acid-catalyzed Etherification of the Tautomers of p-Nitrosophenol and p-Benzoquinoneoxime with Ethanol in Dioxane

The rates of the acid-catalyzed reversible etherification of the allelotrope of p-nitrosophenol and p-benzoquinoneoxime with ethanol in dioxane-forming p-nitrosophenetole have been measured by ultraviolet spectrophotometry. The rate of the forward reaction was expressed as the sum of the second- and the third-orders over a fairly large concentration region of the allelotrope and of ethanol. The plots of the logarithm of the apparent forward second-order rate constant against −log(CBH+⁄CB) gave a straight line with a slope of −0.95. A probable mechanism involving the rate-determining formation of a σ-complex by the nucleophilic attack of the hydroxyl O-atom of ethanol on the α-carbon of the hydroxyl group of protonated p-nitrosophenol, and also the rate-determining deprotonation from the oxime group of the σ-complex by the allelotrope of p-nitrosophenol, was postulated.