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Journal of the Korean Chemical Society (JKCS)

ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 24, Number 1
JKCSEZ 24(1)
February 20, 1980 

 
Title
Nucleophilic Substitution at a Carbonyl Carbon Atom (ⅩⅠ). Solvolysis of Methylchloroformate and Its Thioanalogues in Methanol, Ethanol and Ethanol-Water Mixtures

카르보닐탄소원자의 친핵성 치환반응 (제11보). 메탄올, 에탄올 및 에탄올-물 혼합용매중에서 메틸클로로훠메이트와 그 티오유도체들의 가용매분해반응에 관한 연구
Author
Sangmoo La, Kyeong Shin Koh, Ikchoon Lee

나상무, 고경신, 이익춘
Keywords
Abstract
메탄올, 에탄올 및 에탄올-물 혼합용매중에서 메틸클로로휘메이트, 메틸티올클로로휘메이트, 메틸티오노클로로휘메이트 및 메틸디티오클로로휘메이트의 가용매분해반응에 대한 속도상수를 전기전도도법으로 구하고 활성화 파라미터를 계산하였다. 결과로 메틸클로로휘메이트는 항상 Sn2 메카니즘으로 반응하며, 가수분해 순위는 CH3S(CS)Cl > CH3S(CO)Cl > CH3O(CS)Cl > CH3O(CO)Cl 로 Sn1 반응성이 감소하고, 메탄올에서는 CH3S(CS)Cl은 Sn1으로, 기타는 Sn2로 반응하고, 에탄올에서는 모두 Sn2로 반응하나 아직도 메틸클로로디티오휘메이트는 Sn1 반응성이 어느정도 작용함을 알았다. 또한 에탄올-물 혼합용매에서 물함량이 큰 부분에서는 티오치환체의 Sn1 반응성이 증가하며 메틸클로로디티오휘메이트는 Sn1으로 반응함을 알았다. 에탄올-물 혼합용매중에서 Sn1 반응성의 순위는 가수분해속도의 순위와 같았다.

Solvolysis rate constants for methylchloroformate, methylthionochloroformate, methylthiolchloroformate and methyldithiochloroformate have been determined conductometrically in methanol, ethanol and ethanol-water mixtures and activation parameters have been derived. Results show that methylchloroformate solvolyzes through SN2 process while methyldithiochloroformate solvolyzes by SN1 process in all the solvent systems.The rate of hydrolysis decreased in the order, CH3S(CS)Cl > CH3S(CO)Cl > CH3O(CS)Cl > CH3O(CO)Cl which corresponds to the order of decreasing SN1 character. In methanol, CH3S(CS)Cl solvolyzed via the SN1 mechanism while the others solvolyzed via the SN2 process. In ethanol, however, SN2 character was dominant for all the compounds, except methyldithiochloroformate, for which SN1 character was still strong enough to accelerate the rate of ethanolysis. In ethanol-water mixtures, CH3S(CO)Cl and CH3O(CS)Cl solvolyzed via SN2 process in ethanol-rich region while the SN1 character increased greatly in water-rich region for the solvolysis of these compounds. The order of SNl character for solvolysis in water-rich region was the same as the order of hydrolysis rate.

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