Nucleophilic Substitutions at a Carbonyl Carbon Atom (ⅩⅡ). Solvolysis of Methylchloroformate and Its Thioanalogues in $CH_3CN-H_2O$ and $CH_3COCH_3-H_2$ Mixtures

카르보닐탄소원자의 친핵성 치환반응 (제 12 보).아세토니트릴-물 및 아세톤-물 혼합용 매속에서 메틸클로로훠메이트와 그 티오유도체들의 가용매분해반응에 관한 연구

  • Sangmoo La (Department of Chemical Engineering, Ajou Institute of Technology) ;
  • Kyeong Shin Koh (Department of Chemistry, Chung-ang University) ;
  • Ikchoon Lee (Department of Chemistry, Inha University)
  • 나상무 (아주공과대학 화학공학과) ;
  • 고경신 (중앙대학교 문리과대학 화학과) ;
  • 이익춘 (인하대학교 이과대학 화학과)
  • Published : 19800230

Abstract

Solvolysis rate constants for methylchloroformate, $CH_3O$(CO)Cl, methylthiono-chloroformate, $CH_3O$(CS)Cl, and methylthiolchloroformate, $CH_3S$(CO)Cl, have been determined conductometrically in acetone-water and acetonitrile-water mixtures, and activation parameters, ${\Delta}H^{\neq}$ and ${\Delta}S^{\neq}$, have been derived. Results show that in water-rich regions the order of rate increases as $$CH_3O(CO)Cl while in dipolar aprotic solvent-rich region this order reverses. The plots of log k vs. solvent parameters, Y, $\frac{D-1}{2D+1}$ and log($H_2$) show that the order of rate increase in water-rich region is the results of increase in $S_N1$ character. It is concluded that $CH_3S$(CO)Cl solvolyzes via $S_N1$ mechanism whereas $CH_3O$(CO)Cl reacts via $S_N2$ and $CH_3O$(CS)Cl via intermediate mechanism in water-rich region.

Keywords

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