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이종팔,Ae Ri Bae,엄익환 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.6
A kinetic study is reported for nucleophilic substitution reactions of 4-pyridyl X-substituted benzoates 7a-e with a series of alicyclic secondary amines in H_2O. The Brønsted-type plot for the reactions of 4-pyridyl benzoate 7c is linear with β_(nuc) = 0.71. The corresponding reactions of 2-pyridyl benzoate 6, which is less reactive than 7c, resulted in also a linear Brønsted-type plot with β_(nuc) = 0.77. The fact that the more reactive 7c results in a smaller β_(nuc) value appears to be in accord with the reactivity-selectivity principle. The aminolysis of 7c has been suggested to proceed through a stepwise mechanism in which breakdown of the intermediate is the rate-determining step (RDS). The Hammett plot for the reactions of 7a-e with piperidine consists of two intersecting straight lines, i.e., ρX = 1.47 for substrates possessing an electron-donating group (EDG) and ρX =0.91 for those possessing an electron-withdrawing group (EWG). In contrast, the corresponding Yukawa-Tsuno plot exhibits excellent linear correlation with ρX = 0.79 and r = 0.56. Thus, it has been concluded that the nonlinear Hammett plot is not due to a change in the RDS but is caused by stabilization of the ground state of the substrates possessing an EDG through resonance interaction between the EDG and the C=O bond of the substrates.
N-furoyl-4(5)-nitroimidazole의 가수분해반응에 미치는 촉매효과
이종팔,임춘영 동아대학교 기초과학연구소 2003 基礎科學硏究論文集 Vol.20 No.1
N-furoyl-4(5)-nitroimidazole의 가수분해반응을 25℃에서 분광광도법에 의해 속도론적으로 조사하였다. pH 6.5 이하에서 pH에 무관한 반응과 pH 6.5 이상에서 OH에 의한 촉매반응이 관찰되었다. 가수분해반응속도에 미치는 니트로기의 치환기 효과는 그다지 크게 나타나지 않았다. bifunctional acid & base catalyst 들은 촉매작용은 cacodylate가 가장 효과적이었으며, 염기성형 촉매가 산성형 촉매효과 보다 크게 작용함을 알 수 있었다. 반면 acetate는 촉매효과가 거의 나타나지 않았다. 활성화 엔탈피보다 활성화 엔트로피가 크게 나타났으며 용매동위원소효과가 관찰되었다. The rate constants for the hydrolysis of N-furoyl-4(5)-nitroimidazole are determined in water at the 25℃ under pseudo first order conditions by uv/vis spectrophotometer. The pH independent reaction and the hydroxide ion catalyzed reaction are observed from pH 6.5 to 1.0 and above pH 6.5, respectively. The D₂O solvent isotope effect is observed in the pH independent reaction, that is, k_(0)^(H₂O)/K_(0)^(D₂O)2.0. Activation parameters in the water catalyzed reaction and the hydroxide ion catalyzed reaction are calculated to △H ≠ 9.97 Kcal/mol, △H ≠ 8.51 Kcal/mol and △S ≠ 36.6 e,u., △S ≠-67.1 e.u. respectively. Thus, the water catalyzed reaction and the hydroxide ion catalyzed reaction are more important to nucleophilic attack to the carbonyl carbon than the protonation of the leaving group in the transition state. The most effective catalyst of bifunctional catalysts in the hydrolytic reaction is cacodylate and the base form of this catalyst is more effective, whereas there is no catalytic effect on the acetate.