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엄익환,Eun-JuLee,Jong-PalLee 대한화학회 2002 Bulletin of the Korean Chemical Society Vol.23 No.3
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 H 2 O containing 20 mole % DMSO at 25.0 o C. 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 Brønsted-type plots for the aminolyses of 1a, 1b and 1c are linear with a β 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 ρ − value ( ρ − = 3.11) when σ − constants are used. The linear Brønsted and Hammett plots with large β nuc and ρ − values suggest that the aminolysis of 1a proceeds via rate-determining break-down of the addition intermediate to the products.