s-Triazines. Part V. Synthesis and hydrolytic stability of 2,4-dihalogeno-6-heteroaryl-s-triazines

Abstract

The first and second hydrolysis rate coefficients for the title compounds are discussed in terms of variation of the heteroaryl substituent (substituted phenyl, furyl, pyrrolyl, or thienyl) and of the halogen substituents (X = F, Cl, I, or CCl₃). Electron-withdrawing substituents in the aryl rings enhance the rate coefficients, which are linearly related to the pK_a values of the analogous dioxo-products (III) for phenyl, thienyl, or pyrrolyl substituents. Evidence is presented to show that the rate-determining step in the hydrolysis is nucleophilic attack on the triazine rather than carbon–halogen bond rupture.