2-Adamantyl Halothioformates의 가용매 분해반응에 대한 속도론적 연구

Abstract

순수 용매 및 이성분 혼합 용매 내에서 2-adamantyl chlorothioformate (2-AdSCOCl) 및 2-adamantyl fluorothioformate (2-AdSCOF) 의 가용매 분해반응에 대한 속도 상수를 25.0 oC에서 적정법과 전도도법을 이용하여 측정하였다. 두 물질들의 가용매 분해반응 속도들을 Grunwald-Winstein (G-W) 식에 각각 적용하였다. 그 결과, 2-AdSCOCl는 전체 용매에 대하여 l = 0.04 ± 0.11, m = 0.60 ± 0.07, R = 0.960이 얻어졌다. 그리고 2-AdSCOF는 TFE-H2O, HFIP-H2O 용매들 (fluoro alcohols) 을 제외한 친핵성이 강한 혼합 용매 내에서는 l = 2.98 ± 0.40, m = 1.09 ± 0.09, R = 0.971이 얻어졌고, 친전자적 혼합 용매인 fluoroalcohol 용매들 내에서는 l = 0.56 ± 0.46, m = 1.96 ± 0.76, R = 0.967임을 확인하였다. 또한 활성화 파라미터에 관한 것들은 2-AdSCOCl에서 ΔH≠ = 19.0 ~ 20.8 kcal · mol-1와 ΔS≠ = -19.2 ~ -3.8 cal · mol-1 · K-1 이고, 2-AdSCOF는 fluoroalcohol을 제외한 친핵적 혼합 용매 내에서 ΔH≠= 12.5 ~ 16.7 kcal · mol-1와 ΔS≠= -44.5 ~ -32.2 cal · mol-1 ·K-1 이며, fluoroalcohol 에서는 ΔH≠= 20.4 ~ 28.1 kcal · mol-1, ΔS≠= -15.3 ~ -0.1 cal · mol-1 · K-1 값을 얻었다. 또한 2-AdSCOCl와 2-AdSCOF의 가용매 분해반응의 생성물에 대한 선택성, 용매 동위원소 효과, 그리고 이탈기의 효과 등을 부가적으로 연구하였다. 이상의 결과들로부터 2-AdSCOCl의 가용매 분해반응은 모든 용매 내에서 이온화 반응 경로로 진행되며, 2-AdSCOF의 가용매 분해반응은 친핵성도가 큰 용매에서는 사면체 중간생성물을 거치는 첨가-제거 반응이 지배적이나, 그 이외의 다른 용매 내에서는 주된 반응이 이온화 반응임을 알았다.|The rate constants of the solvolysis of 2-adamantyl chlorothioformate (2-AdSCOCl) and 2-adamantyl fluorothioformate (2-AdSCOF) have been measured using both autotitration and electric conductivity methods at 25.0 oC in pure and binary organic solvents. The Grunwald-Winstein equation has been applied to determine the reaction mechnisms of two substrates. From the results of the Grunwald-Winstein equation analyses, in 2-AdSCOCl solvolysis, the ionization pathway (l=0.04, m=0.60, and l/m=0.07) was dominant in all solvents. Unlike the reactions in hydroxylic solvents of 2-AdSCOCl, where only ionization pathway was observed, the solvolyses of 2-AdSCOF have two major reaction pathways: a parallel ionization pathway and a pathway involving bimolecular attack by solvent at acyl carbon, by what is suggested to be an addition-elimination mechanism. Entropies of activation for attack at acyl carbon (ΔS≠= -44.5 ~ -32.2 cal ·mol-1 ·K-1) are considerably more negative than for a concerted fission of the 2-Ad-S and C-Cl bonds with SCO formation (via solvolysis-decomposition) and the rate detennining formation of a 2-AdSCO+X- ion pair (via a carboxylium ion) (ΔS≠ = -19.2 ~ -0.1 cal ·mol-1 ·K-1). The kF/kCl ratios for 2-AdSCOXsolvolysis in TFE-H2O solvents are in the range of ~ 10-4, suggesting appreciable C-X bond breaking in the transition state of the rate-determining step. The kinetic solvent isotope effects (KSIEs, kMeOH/kMeOD), and the selectivity values (S) for each solvent composition for the solvolyses of 2-AdSCOCl and 2-AdSCOCF were also calculated. The results are compared with those reported earlier for other 2-adamantyl haloformates and mechanistic conclusions are drawn.; The rate constants of the solvolysis of 2-adamantyl chlorothioformate (2-AdSCOCl) and 2-adamantyl fluorothioformate (2-AdSCOF) have been measured using both autotitration and electric conductivity methods at 25.0 oC in pure and binary organic solvents. The Grunwald-Winstein equation has been applied to determine the reaction mechnisms of two substrates. From the results of the Grunwald-Winstein equation analyses, in 2-AdSCOCl solvolysis, the ionization pathway (l=0.04, m=0.60, and l/m=0.07) was dominant in all solvents. Unlike the reactions in hydroxylic solvents of 2-AdSCOCl, where only ionization pathway was observed, the solvolyses of 2-AdSCOF have two major reaction pathways: a parallel ionization pathway and a pathway involving bimolecular attack by solvent at acyl carbon, by what is suggested to be an addition-elimination mechanism. Entropies of activation for attack at acyl carbon (ΔS≠= -44.5 ~ -32.2 cal ·mol-1 ·K-1) are considerably more negative than for a concerted fission of the 2-Ad-S and C-Cl bonds with SCO formation (via solvolysis-decomposition) and the rate detennining formation of a 2-AdSCO+X- ion pair (via a carboxylium ion) (ΔS≠ = -19.2 ~ -0.1 cal ·mol-1 ·K-1). The kF/kCl ratios for 2-AdSCOXsolvolysis in TFE-H2O solvents are in the range of ~ 10-4, suggesting appreciable C-X bond breaking in the transition state of the rate-determining step. The kinetic solvent isotope effects (KSIEs, kMeOH/kMeOD), and the selectivity values (S) for each solvent composition for the solvolyses of 2-AdSCOCl and 2-AdSCOCF were also calculated. The results are compared with those reported earlier for other 2-adamantyl haloformates and mechanistic conclusions are drawn.