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

Solvolysis rate constants for methylchloroformate, CH3O(CO)Cl, methylthiono-chloroformate, CH3O(CS)Cl, and methylthiolchloroformate, CH3S(CO)Cl, have been determined conductometrically in acetone-water and acetonitrile-water mixtures, and activation parameters, ΔH≠ and ΔS≠, have been derived. Results show that in water-rich regions the order of rate increases as CH3O(CO)Cl < CH3O(CS)Cl < CH3S(CO)Cl while in dipolar aprotic solvent-rich region this order reverses. The plots of log k vs. solvent parameters, Y, (D - 1) / (2D + 1) and log(H2O) show that the order of rate increase in water-rich region is the results of increase in SN1 character. It is concluded that CH3S(CO)Cl solvolyzes via SN1 mechanism whereas CH3O(CO)Cl reacts via SN2 and CH3O(CS)Cl via intermediate mechanism in water-rich region.