EQUILIBRIUM AND KINETIC-STUDY OF PIPERIDINE BINDING TO PHTHALOCYANINATOIRON(II) IN DIMETHYL-SULFOXIDE

The reaction between piperidine (Pip) and phthalocyaninatoiron(II) ([Fe(pc)]) in dimethyl sulfoxide (dmso) has been studied at 20.0-degrees-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) = k1f[Pip] + k1r with k1f' = (8.7 +/- 0.2) X 10(3) dm3 mol-1 s-1 and k1f'' = (8.3 +/- 0.2) x 10(1) dm3 mol-1 s-1, for the binding of the first and second Pip molecule, respectively. Equilibrium experiments yield K1' = (1.0 +/- 0.1) x 10(5) dm3 mol-1 and K1'' = (1.3 +/- 0.1) X 10(3) dm3 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 (k1f' and k1f'') and of the equilibrium constants (K1' and K1''), the dissociation rate constants have been estimated to be k1r'= (8.7 +/- 1) x 10(-2) s-1 and k1r'' = (6.4 +/- 0.7) x 10(-2) s-1. Present results are discussed in the light of related previous studies.