Equilibrium and kinetic study of piperidine binding to phthalocyaninatoiron(II) in dimethyl sulfoxide

Abstract

The reaction between piperidine (Pip) and phthalocyaninatoiron(II) ([Fe(pc)]) in dimethyl sulfoxide (dmso) has been studied at 20.0 °C, from both equilibrium and kinetic viewpoints. In excess of Pip, the adduct [Fe(pc)(Pip) 2] is formed via two consecutive pseudo-first-order processes. The observed rate constants have the general form: k obs= k 1f[Pip] + k 1r with k 1f′ = (8.7 ± 0.2) × 10 3 dm 3 mol −1 s −1 and k 1f″ = (8.3 ± 0.2) × 10 1 dm 3 mol −1 s −1, for the binding of the first and second Pip molecule, respectively. Equilibrium experiments yield K 1′ = (1.0 ± 0.1) × 10 5 dm 3 mol −1 and K 1″ = (1.3 ± 0.1) × 10 3 dm 3 mol −1 for the stepwise formation of the [Fe(pc)(dmso)(Pip)] and [Fe(pc)(Pip) 2] adducts, respectively. From the values of the second-order rate constants ( k 1f′ and k 1f″) and of the equilibrium constants ( K 1′ and K 1″), the dissociation rate constants have been estimated to be k 1r′= (8.7 ± 1) × 10 −2 s −1 and k 1r″ = (6.4 ± 0.7) × 10 −2 s −1. Present results are discussed in the light of related previous studies.