Journal of the Korean Chemical Society (대한화학회지)

Korean Chemical Society (대한화학회)
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Mechanism of the Hydrolysis of Phenyl N-(p-chlorobenzoyl)Chloroformimidate Derivatives in Acid Media

산성용액 중에서 Phenyl N-(p-chlorobenzoyl)chloroformimidate 유도체의 가수분해 반응 메카니즘

  • Nack-Do Sung (Department of Agricultural Chemistry, Chungnam National University) ;
  • Young-Gu Cheun (Daejon Machine Development) ;
  • Ki-Sung Kwon (Department of Chemistry, Chungnam National University) ;
  • Tae-Rin Kim (Department of Chemistry, Korea University)
  • 성낙도 (충남대학교 농과대학 농화학과) ;
  • 전용구 (대전 기계창) ;
  • 권기성 (충남대학교 자연과학대학 화학과) ;
  • 김태린 (고려대학교 이과대학 화학과)
  • Published : 1987.08.20
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Abstract

Rate constants for the hydrolysis of para-substituted phenyl N-(p-chlorobenzoyl)chloroformimidate (I) derivatives in 1 : 4 dioxane-water at $25^{\circ}C$ have been determined. Rate data, substituent effect $(\rho\>{\rho}^+)$, product analysis and MO calculation indicate that the uncatalyzed reaction proceeds through an $S_N1$ mechanism involving the formation of azocarbonium ion (II) below pH 3.0, and the base-catalyzed reaction proceeds through an $S_N2$ mechanism via transition state (III) above pH 4.0. The relative stability of four peri planar conformational isomers were (E-ap) > (Z-ap) > (E-sp) > (Z-ap), respectively, and the most stable stereo structures shows that the Y-substituted phenyl group $(C_6H_4-Y)$ occupy vertical $(90^{\circ})$ position on the plane of the benzimidochloroformyl group in (E-ap) conformer. The nucleophilic substitution of water molecule occurs by sigma attack to the activatived azomethine carbon atom of (I) derivatives.

$25^{\circ}C$의 1 : 4 dioxane-물의 혼합용액속에서 파라-치환된 phenyl N-(p-chlorobenzoyl)chloroformimidate (I) 유도체들의 가수분해 반응속도 상수를 측정하고 반응속도식, 치환기 효과$(\rho\>{\rho}^+)$, 생성물 분석 및 분자궤도 함수의 계산 결과로부터 pH3.0 이하에서는 azocarbonium 이온(II)이 생성되는 $S_N1$반응 메카니즘으로 무촉매 반응이 일어나며, pH 4.0이상에서는 전이상태(III)를 지나는 $S_N2$반응 메카니즘을 통하여 염기 촉매반응이 일어남을 제안 할 수 있었다. 4가지 peri planar형태 이성질체들의 상대적인 안정도는 각각 (E-ap) > (Z-ap) > (E-sp) > 및 (Z-ap)이었고, (E-ap)형태의 가장 안정한 입체구조는 benzimidochloroformyl group면에 대하여 Y-치환 phenyl group이 수직$(90^{\circ})$을 이루었으며 (I)의 활성화된 azomethine탄소 원자에 대하여 물분자는 시그마 공격에 의하여 친핵성 반응이 일어난다.

Keywords

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