Kinetics and Mechanism for the Reaction of 4-Nitrophenyl 2-Furoate with Secondary Alicyclic Amines

Second-order-rate constants (kN) have been measured spectrophotometrically for the reactions of 4-nitrophenyl 2-furoate (1) with a series of secondary alicyclic amines in H2O containing 20 mole % DMSO at 25.0 oC. 1 is about 5-8 times more reactive than 4-nitrophenyl benzoate (2), although 1 is expected to be less reactive than 2 based on MO calculations and 13C NMR study. The Brφnsted-type plots for the aminolysis reactions of 1 and 2 are linear with βnuc values of 0.78 and 0.85, respectively. The replacement of the CH=CH group by an O atom in the acyl moiety (2 → 1) does not cause any mechanism change. The reaction of piperidine with a series of substituted phenyl 2-furoates gives a linear Hammett plot with a large ρ – value (ρ – = 2.88) when σ – constants are used. The linear Brφnsted and Hammett plots with a large ρ – value suggest that the aminolysis reaction of 1 proceeds via rate-determining break-down of the addition intermediate to the porducts