Nucleophilic attack on the carbon–carbon double bond. I. Reaction of primary and secondary amines with 2,2-di(4-nitrophenyl)-1,1-difluoroethene

Abstract

The reaction of primary and secondary amines with 2,2-di(4-nitrophenyl)-1,1-difluoroethene (1) in acetonitrile solvent gives first 2,2-di(4-nitrophenyl)-1-fluoro-1-aminoethene (2) and then 2,2-di(4-nitrophenyl)-1,1-difluoro-1-aminoethane (3). With excess amine, pseudo-first-order rate constants for the production of 2 were measured, which showed a second-order reaction, together with a catalysed third-order reaction. In addition to the reagent amines, the reaction is also catalysed by tertiary amines and bases such as oxalate and acetate, but not by chloride and perchlorate, nor by ammonium ions. The enthalpy of activation for the reaction of piperidine with 1 in acetonitrile is 3.7 kcalmol−1, but for the catalysed reaction an apparent value of −2.2 kcal mol−1 was obtained. It is concluded that the reaction proceeds via a pre-equilibrium to a zwitterion, followed by another equilibrium giving a carbanion that yields the product (2) by a rate-determining cleavage of the carbon–fluorine bond.