Metal-ion-promoted hydrolysis of methyl 8-hydroxyquinoline-2-carboxylate

Abstract

Base hydrolysis of the title compound (EH) has been studied over the range pH 9.18–12.1 and values of k_OH determined for EH (k_OH 4.0 dm³ mol^–1 s^–1) and for the anion E^–(k_OH 0.485 dm³ mol^–1 s^–1) at 25 °C and I= 0.1 mol dm^–3. Formation constants K_ME⁺ have been obtained at 25 °C and I= 0.1 mol dm³ for the equilibrium M²⁺+ E^–⇌[ME]⁺ using both spectrophotometric and kinetic methods. Rate constants for the base hydrolysis of the [ME]⁺ complexes (M^II= Mn^II, Co^II, Ni^II, Cu^II, or Zn^II) have been determined together with the values of ΔH^‡ and ΔS^‡ at 298 K. Quite large rate accelerations are observed (10³–10⁶) when comparisons are made with the base hydrolysis of E^–. The origin of the rate accelerations is discussed in terms of the thermodynamic activation parameters obtained and possible mechanisms for the reaction are considered.