ACID-CATALYZED HYDROLYSIS OF N-VINYLACETAMIDES (ENAMIDES) - SUBSTITUENT EFFECTS OF THE ACETAMIDO-GROUPS AND AMINO-GROUPS AND LINEAR FREE-ENERGY CORRELATIONS OF CYCLOHEXENE REACTIVITIES

The rates of acid-catalyzed hydration of N-vinylacetamide (1), N-(2-propenyl)acetamide (2), N-(1-phenylvinyl)-acetamide (3), and N-(1-cyclohexenyl)acetamide (4) have been measured. These compounds react through rate-limiting protonation on carbon (the ASE2 mechanism) as evidenced by the observation of general acid catalysis for 2, the solvent isotope effect kH3O+/kD3O+for 1, 3, and 4, and the correlation of the reactivity of 1-3 with the substituent effect-rate correlation established for this mechanism. A contrary mechanism previously proposed for 2-arylenamides is not substantiated. A new linear free energy correlation of the rates of hydration of 1 -substituted cyclohexenes is established and also supports the ASE2 mechanism for 4. A σp+of -0.65 for the acetamido substituent is most compatible with these hydration results and data on various chemical processes available in the literature. Hydration rates of p-acetamidostyrene (5) and p-acetamido-α-mcthylstyrene (6) define a value of σp+for acetamido of -0.33 applicable to substituted styrcnes. Literature data for the effect of amino substituents on the hydration of alkenes and styrenes are also analyzed and all of the data are satisfactorily accommodated by our previously proposed relationship log k2= -10.5Σσp+- 8.92. Over 110 compounds spanning 23 powers of ten in reactivity are included, with only modest curvature suggesting minimal saturation of the substituent effects. © 1979, American Chemical Society. All rights reserved.