[Kinetics of the reaction of 2,4-dinitro-1-fluorobenzene with imidazole-SH-, and imidazole-SH-compounds].

Abstract

First order rate constants of the reaction of a series of SH-, imidazole- and imidazole/SH-compounds with FDNB as well as their pH- and temperature dependence were determined. Some of the tested imidazole/SH-compounds exhibit a higher nucleophilic reactivity as is expected on the basis of their pKSH-values. This enhanced reactivity is caused by an activation of the SH-groups by a neighbouring imidazole residue. The pH-independent rate constants were calculated using the Lindley equation. The kinetics of DNP-transfer from DNP-imidazole to SH-compounds were investigated. The pH-dependence of the reaction displays a maximum curve. Donor in this reaction is the DNP-imidazolecation and acceptor the thiolate anion. The reaction rate of FDNB with imidazole derivatives is two to three orders of magnitude slower than with SH-compounds. No inter- or intra-molecular transfer of the DNP-residue from sulfure to imidazole takes place.