Abstract
Rate constants and activation parameters for the methanolysis of t-butyl halide (t-BuCl, t-BuBr, t-BuI) in various MeOH-DMSO mixtures were measured by conductometric method. Taft's solvatochromic parameters, such as polarity-polarizability(SPP's), ${\pi}^{\ast}$, hydrogen bond donor (HBD) acidity, ${\alpha}$, and hydrogen bond acceptor (HBA) basicity, ${\beta}$ of the solvents, were determined by the so called solvatochromic method using five indicators. The variation of methanolysis rate with the solvent composition was discussed on the basis of the activation parameters and the correlation of the rates with the solvatochromic parameters. It is concluded that the polarity-polarizability, HBD acidity and HBA basicity of the mixtures had an effect on the ionization of t-butyl halide cooperatively, also that the specific interaction between the leaving groups and the solvents, such as ion-dipole and hydrogen bond acceptor-donor interaction, is the most important factor of solvent effects on the stabilization of transition states.
MeOH-DMSO 혼합용매중에서 t-butyl halide의 가메탄올 분해반응 속도상수 및 활성화 파라미터를 전기전도도법으로 측정하였고, Taft의 분광용매화 변수인 용매의 극성-편극성(${\pi}^{\ast}$), 수소결합주기산도(${\alpha}$) 및 수소결합 받기염기도(${\beta}$)를 분광법에 의해서 5가지의 지시약을 이용하여 측정계산하였다. 분광용매화변수와 반응속도상수로부터 얻은 활성화파라미터를 써서 용매의 부피조성비에 따른 가용매분해반응의 속도상수 변화를 논의한 결과, t-butyl halide의 이온화에 용매의 ${\pi}^{\ast}$, ${\alpha}$ 및 ${\beta}$가 협동적으로 기여했고, 또한 이탈기와 혼합용매사이의 이온-쌍극자 작용과 수소결합주기-받기 작용과 같은 독특한 상호작용이 전이상태의 안정화에 미치는 가장 중요한 용매효과 인자들임을 밝혔다.
