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

摘要

Second-order-rate constants (k_N) have been measured spectrophotometrically for the reactions of 4-nitrophenyl 2-thiophenecarboxylate (1a) with a series of secondary alicyclic amines in H₂O containing 20 mole % DMSO at 25.0 ∩. The ester 1a is less reactive than 4-nitrophenyl 2-furoate (1b) but more reactive than 4-nitrophenyl benzoate (1c) except towards piperazinium ion. The Br┆nsted-type plots for the aminolyses of 1a, 1b and 1c are linear with a モ_nuc value of 0.92, 0.84 and 0.85, respectively, indicating that the replacement of the CH=CH group by a sulfur or an oxygen atom in the benzoyl moiety of 1c does not cause any mechanism change. The reaction of piperidine with a series of substituted phenyl 2-thiophenecarboxylates gives a linear Hammett plot with a large ヱ- value ( ヱ- = 3.11) when ヲ- constants are used. The linear Br┆nsted and Hammett plots with large モ_nuc and ヱ- values suggest that the aminolysis of 1a proceeds via rate-determining break-down of the addition intermediate to the products.