Substituent effects on the activation parameters of pyridine acylation with esters and thioesters in solution

Abstract

Variation of the activation parameters in the acylation of pyridine with esters and thioesters may be used as a tool for studying mechanisms of acyl transfer reactions in solution. Here, the effect of substituents in benzene and pyridine derivatives on the activation parameters ΔX≠ (where X stands for enthalpy H, entropy S, or Gibbs energy G) in terms of an equation analogous to the Hammett equation is used to estimate the reaction constant δΔX≠. The linear dependence of the reaction constant δΔHint≠ on δΔG≠ provides an alternative way of assessing variations in the pyridine acylation mechanism when one step of the process is the only rate-determining step.