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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 23, Number 3
BKCSDE 23(3)
March 20, 2002 

Kinetics and Mechanism for the Reaction of 4-Nitrophenyl 2-Thiophenecarboxylate with Secondary Alicyclic Amines
Ik-Hwan Um, Eun-Ju Lee, Jong-Pal Lee
Aminolysis, Rate-determining step, Mechanism, Hammett equation.
Second-order-rate constants (kN) 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 Brønsted-type plots for the aminolyses of 1a, 1b and 1c are linear with a βnuc 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 βnuc and ρ- values suggest that the aminolysis of 1a proceeds via rate-determining break-down of the addition intermediate to the products.
381 - 384
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