• 대한화학회지
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• 제39권7호
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• pp.572-577
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• 1995

아세토니트릴 용매계에서 aryl 치환(Z)-benzoate류와 아민류의 반응속도를 15, 25, 및 35 $^{\circ}C$에서 분광학적 방법으로 구했다. 2차 반응속도 상수로부터 Hammett $\rho$값, Bronsted ${\beta}$값, 및 활성화 parameter를 구했으며 이들값과 M-O-F-J diagram 등의 해석으로부터 본 반응은 $S_AN$ 메카니즘으로 진행됨을 알 수 있었다.

• Bulletin of the Korean Chemical Society
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• 제29권10호
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• pp.1915-1919
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• 2008

Second-order rate constants ($k_N$) have been measured spectrophotometrically for reactions of 3,4-dinitrophenyl benzoates (5b) with a series of alicyclic secondary amines in 80 mol % $H_2O$/20 mol % DMSO at 25.0 ${\pm}$ 0.1 ${^{\circ}C}$. The kinetic data have been compared with the data reported previously for the corresponding reactions of 2,4- dinitrophenyl benzoates (5a) to investigate the effect of changing the nucleofuge from 2,4-dinitrophenoxide to 3,4-dinitrophenoxide on reactivity and mechanism. The kinetic results show that aminolyses of 5a and 5b proceed through the same mechanism, i.e., a zwitterionic tetrahedral intermediate ($T^{\pm}$) with a change in the rate-determining step (RDS). Substrate 5a is more reactive than 5b when breakdown of $T^{\pm}$ is the RDS but less reactive when formation of $T^{\pm}$ is the RDS. Dissection of kN values into the microscopic rate constants (e.g., $k_1$ and $k_2/k_{-1 }$ ratio) has revealed that 5a results in larger $k_2/k_{-1}$ ratios but smaller k1 values than 5b for all the amines studied. Since 2,4-dinitrophenoxide is less basic and a better nucleofuge than 3,4-dinitrophenoxide, the larger $k_2/k_{-1}$ ratios determined for the reactions of 5a than for those of 5b are as expected. The steric hindrance exerted by the ortho-nitro group on 5a contributes to the smaller k1 values found for the reactions of 5a than for those of 5b.

• Bulletin of the Korean Chemical Society
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• 제30권10호
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• pp.2403-2407
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• 2009

Second-order rate constants have been measured for two series of nucleophilic displacement reactions, i.e., reactions of 4-nitrophenyl benzoate with Z-substituted phenoxides and those of Y-substituted phenyl benzoates (1a-h) with 4-chlorophenoxide (4-ClPhO–) in 80 mol% $H_2O$/20 mol% DMSO at 25.0 ${\pm}\;0.1\;{^{\circ}C}$. The Br$\phi$nsted-type plot for reactions of 4-nitrophenyl benzoate with Z-substituted phenoxides exhibits an excellent linear correlation with ${\beta}_{nuc}$ = 0.72. Reactions of 1a-h with 4-chlorophenoxide result in also a linear Br$\phi$nsted-type plot with ${\beta}_{lg}$ = –0.62, a typical ${\beta}_{lg}$ value for a concerted mechanism. The Hammett plots correlated with ${\sigma}^o\;and\;{\sigma}^-$ constants show many scattered points for reactions of 1a-h with 4-chlorophenoxide. In contrast, the corresponding Yukawa-Tsuno plot exhibits an excellent linear correlation with $\rho_Y$ = 2.26 and r = 0.53, indicating that expulsion of the leaving group occurs at the rate-determining step (RDS) either in a concerted mechanism or in a stepwise pathway. However, a stepwise mechanism with leaving group departure being the RDS is excluded since the leaving Y-substituted phenoxide is less basic and a better nucleofuge than the incoming 4-ClPh$O^-$. Thus, the reactions have been concluded to proceed through a concerted mechanism, in which bond formation between the nucleophile and electrophilic center is more advanced than expulsion of the leaving group in the transition state on the basis of the magnitude of ${\beta}_{nuc}\;and\;{\beta}_{lg}$ values.

• 한국식품위생안전성학회지
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• 제17권3호
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• pp.166-172
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• 2002

보존료인 소르빈산 및 소르빈산칼륨, 안식향산 및 그 염류, 파라옥시안식향산에스테르류를 중심으로 식품첨가물의 일일추정섭취량을 평가하는 새로운 방법으로서 설문조사법을 제시하여 일일추정섭취량을 구하였을 때 조사한 보존료 모두 일일섭취허용량(ADI)의 1%미만으로 매우 안전한 수준이였다. 기존에 수행된 최대허용량을 이용한 단순추정방법 및 실제 분석치를 이용한 정밀추정방법과 비교ㆍ평가하였을 때, 설문조사법에 의한 총 일일추정섭취량은 소르빈산염류의 경우 0.39 mg/kg bw/day로 실제 분석치를 이용한 정밀조사방법에 의한 값인 0.22 mg/kg bw/day보다 높았으나 최대허용량을 이용한 방법에 의한 값인 1.39mg/kg bw/day보다는 훨씬 낮았다. 또한 안식향산염류와 파라옥시안식향산에스테르의 경우도 설문조사가 0.29 mg/kg bw/day, 0.03 mg/kg bw/day으로 정밀추정방법보다는 높게 나타났으나 단순추정방법인 최대허용량을 이용한 방법보다는 훨씬 낮은 값으로 정밀추정방법에 의한 값에 가까운 결과를 보였다. 따라서 설문조사법을 간편하고 경제적이면서 섭취량을 정밀하게 추정할 수 있는 식품첨가물 섭취량 평가의 방법으로 활용할 수 있을 것으로 사료된다.

• Bulletin of the Korean Chemical Society
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• 제31권7호
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• pp.2015-2018
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• 2010

Second-order rate constants $(k_{OH^-})$ have been measured spectrophotometrically for alkaline hydrolysis of Y-substituted phenyl phenyl carbonates (2a-j) and compared with the $k_{OH^-}$ values reported previously for the corresponding reactions of Y-substituted phenyl benzoates (1a-j). Carbonates 2a-j are 8~16 times more reactive than benzoates 1a-j. The Hammett plots correlated with $\sigma^-$ and $\sigma^o$ constants exhibit many scattered points, while the Yukawa-Tsuno plot results in excellent linear correlation with $\rho$ = 1.21 and $\gamma$ = 0.33. Thus, the reaction has been concluded to proceed through a concerted mechanism in which expulsion of the leaving group is advanced only a little. However, one cannot exclude a possibility that the current reaction proceeds through a forced concerted mechanism with a highly unstable intermediate.

• Bulletin of the Korean Chemical Society
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• 제29권3호
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• pp.580-584
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• 2008

Second-order rate constants (kN) have been measured spectrophotometrically for reactions of Y-substituted phenyl benzoates (1a-h) with azide ion (N3) in 80 mol % H2O/20 mol % DMSO at 25.0 0.1 oC. The Brnsted-type plot for the azidolysis exhibits a downward curvature, i.e., the slope (b lg) changes from 0.97 to 0.20 as the basicity of the leaving group decreases. The pKao (defined as the pKa at the center of the Brnsted curvature) is 4.8, which is practically identical to the pKa of the conjugate acid of N3 ion (4.73). Hammett plots correlated with s o and s constants exhibit highly scattered points for the azidolysis. On the contrary, the corresponding Yukawa-Tsuno plot results in an excellent linear correlation with r = 2.45 and r = 0.40, indicating that the leaving group departs in the rate-determining step. The curved Brnsted-type plot has been interpreted as a change in the rate-determining step in a stepwise mechanism. The microscopic rate constants (k1 and k2/k1 ratio) have been calculated for the azidolysis and found to be consistent with the proposed mechanism.

• Bulletin of the Korean Chemical Society
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• 제31권12호
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• pp.3588-3592
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• 2010

Second-order rate constants ($k_N$) have been measured spectrophotometrically for nucleophilic substitution reactions of 2-pyridyl X-substituted benzoates 8a-e with a series of alicyclic secondary amines in $H_2O$ at $25.0{\pm}0.1^{\circ}C$. The $k_N$ values for the reactions of 8a-e are slightly smaller than the corresponding reactions of 4-nitrophenyl X-substituted benzoates 1a-e (e.g., $kN^{1a-e}/k_N^{8a-e}$ = 1.1 ~ 3.1), although 2-pyridinolate in 8a-e is ca. 4.5 $pK_a$ units more basic than 4-nitrophenolate in 1a-e. The Br$\o$nsted-type plot for the aminolysis of 8c (X = H) is linear with $\beta_{nuc}$ = 0.77 and $R^2$ = 0.991 (Figure 1), which is typical for reactions reported previously to proceed through a stepwise mechanism with breakdown of a zwitterionic tetrahedral intermediate $T^{\pm}$ being the rate-determining step (RDS), e.g., aminolysis of 4-nitrophenyl benzoate 1c. The Hammett plot for the reactions of 8a-e with piperidine consists of two intersecting straight lines (Figure 2), i.e., $\rho$ = 1.71 for substrates possessing an electron-donating group (EDG) while $\rho$ = 0.86 for those bearing an electron-withdrawing group (EWG). Traditionally, such a nonlinear Hammett plot has been interpreted as a change in RDS upon changing substituent X in the benzoyl moiety. However, it has been proposed that the nonlinear Hammett is not due to a change in RDS since the corresponding Yukawa-Tsuno plot exhibits excellent linear correlation with $\rho$ = 0.85 and r = 0.62 ($R^2$ = 0.995, Figure 3). Stabilization of substrates 8a-e in the ground state has been concluded to be responsible for the nonlinear Hammett plot.

• 대한화학회지
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• 제39권8호
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• pp.657-665
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• 1995

여러가지 비대칭 벤질 에테르들과 벤질 알킬 에테르들을 $CH_3CO_2Et$-NaOCI수용액(6.6 mol eq.)의 2상 용매계에서 4-methoxy-2, 2, 6, 6,-tetramethylpiperidine-1-oxyl(0.03 mol eq., 4-methoxy-TEMPO)을 이용하여 산화시키면 벤조에이트로 산화가 일어난다. 4-methoxy-TEMPO는 2차 산화제인 NaOCI에 의하여 본반응의 산화제인 N-oxo-4-2, 2, 6, 6, -tetramethyl-piperidium 염(N-oxoammonium 염)으로 변환된다. N-oxoammonium 염은 에테르를 산화시키고 N-hydroxy-4-methoxy-2, 2, 6, 6,-tetramethylpiperidine(hydroxyamine)으로 환원된다. Hydroxy-amine은 NaOCI에 의하여 N-oxoammonium 염으로 순환 재생되므로 4-methoxy-TEMPO는 촉매량 사용하였다. 이 반응은 또한 조촉매인 KBr(0.03 mol eq.)가 필수적이고 반응 중 pH는 8.0 이하로 유지되어야 한다. 0 - 5$^{\circ}C$의 반응 온도로 2.5시간 반응시키면 대부분 벤조에이트로 산화 되었다. 벤질 알킬 에테르들의 선택성 산화는 수소의 산도와 알킬기의 입체효과에 영향을 받음이 고찰되었다.

• Bulletin of the Korean Chemical Society
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• 제32권6호
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• pp.1907-1911
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• 2011

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 H2O. The Br${\o}$nsted-type plot for the reactions of 4-pyridyl benzoate 7c is linear with ${\beta}_{nuc}$ = 0.71. The corresponding reactions of 2-pyridyl benzoate 6, which is less reactive than 7c, resulted in also a linear Br${\o}$nsted-type plot with ${\beta}_{nuc}$ = 0.77. The fact that the more reactive 7c results in a smaller ${\beta}_{nuc}$ 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., ${\rho}_X$ = 1.47 for substrates possessing an electron-donating group (EDG) and ${\rho}_X$ = 0.91 for those possessing an electron-withdrawing group (EWG). In contrast, the corresponding Yukawa-Tsuno plot exhibits excellent linear correlation with ${\rho}_X$ = 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.

• Bulletin of the Korean Chemical Society
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• 제31권9호
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• pp.2593-2597
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• 2010

Second-order rate constants ($k_N$) have been measured spectrophotometrically for reactions of 2,4-dinitrophenyl X-substituted benzoates (X = 4-MeO, H and 4-$NO_2$) with a series of Z-substituted pyridines in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. The Br${\o}$nsted-type plots exhibit downward curvature (e.g., $\beta_2$ = 0.89 ~ 0.96 when $pK_a$ < 9.5 while $\beta_1$ = 0.38 ~ 0.46 when $pK_a$ > 9.5), indicating that the reaction proceeds through a stepwise mechanism with a change in rate-determining step (RDS). The ${pK_a}^o$, defined as the $pK_a$ at the center of Br${\o}$nsted curvature, has been analyzed to be 9.5 regardless of the electronic nature of the substituent X in the benzoyl moiety. Dissection of $k_N$ into the microscopic rate constants $k_1$ and $k_2/k_{-1}$ ratio has revealed that $k_1$ is governed by the electronic nature of the substituent X but the $k_2/k_{-1}$ ratio is not. Theoretical calculations also support the argument that the electronic nature of the substituent X in the benzoyl moiety does not influence the $k_2/k_{-1}$ ratio.