PROTON TRANSFER FROM CYANOCARBON ACIDS .I. GENERAL BASE CATALYZED DETRIATION OF 1,4-DICYANO-2-BUTENE-1-T IN AQUEOUS SOLUTION

Detritiation of 1,4-dicyanobutene-1-t in water is a measurably slow base-catalyzed reaction at 25°. General base catalysis is observed with amine and phenolate bases; the BrØnsted βis 0.94 for the phenolate bases and 0.98 for secondary amines. For hydroxide ion catalyzed detritiation the activation parameters are: Ea = 15.3 kcal mole-1 and ∆S‡ = -21.5 eu with k in M-1 sec-1 units. The primary hydrogen kinetic isotope effect is kh/KD = 3.9. No catalysis by the base water could be detected at 50°. A tentative value of 21 was obtained for the pKa of this cyanocarbon. From these data approximate values have been calculated for the rates of the reverse reaction of carbanion with the conjugate acid species; these values approach the diffusion limit. Evidence that, for the systems studied, the fast process is not, however, actually diffusion controlled comes from the fact that the Br0nsted α and βslopes have not attained their limiting values of zero and unity and from the further fact that a modest degree of steric hindrance is observed. Overall, the data strongly suggest that the slow process is a straightforward bimolecular slow proton removal. © 1969, American Chemical Society. All rights reserved.