title: Nucleophilic substitution reactions of aryl dithioacetates with pyridines in acetonitrile.
abstract: Kinetic studies of the pyridinolysis (XC(5)H(4)N) of aryl dithioacetates (CH(3)C(=S)SC(6)H(4)Z) are carried out in acetonitrile at 60.0 degrees C. A biphasic Brönsted plot is obtained with a change in slope from a large value (beta(X) congruent with 0.9) to a small value (beta(X) congruent with 0.4) at pK(a) degrees = 5.2, which is attributed to a change in the rate-limiting step from breakdown to formation of a zwitterionic tetrahedral intermediate, T(+/-), in the reaction path as the basicity of the pyridine nucleophile increases. A clear-cut change in the cross-interaction constants rho(XZ) from a large positive value (rho(XZ) = +1.34) to a small negative value (rho(XZ) = -0.15) supports the mechanistic change proposed.
authors.affiliation: Department of Chemistry, Chonbuk National University, Chonju, 560-756 Korea.
authors.forename: Hyuck Keun
authors.initials: HK
authors.lastname: Oh
authors.forename: Myoung Hwa
authors.initials: MH
authors.lastname: Ku
authors.forename: Hai Whang
authors.initials: HW
authors.lastname: Lee
authors.forename: Ikchoon
authors.initials: I
authors.lastname: Lee