Dodecylpyrazinium halides: their synthesis, characterisation and use in the micellar catalysis of the aquation of tris(1,10-phenanthroline)iron(II) perchlorate in aqueous perchloric acid medium

Abstract

The synthesis and characterisation of the new surfactant system dodecylpyrazinium chloride (DPC) and its effect on the rate of aquation of tris(1,10-phenanthroline)iron(II) perchlorate in aqueous perchloric acid solution are described. The aquation rate of the complex is accelerated by a factor of 10, from ca. 10^–5 to ca. 10^–4 s^–1, in the presence of DPC. This increase is suggested to be due to an additional equilibrium pathway for removal of phenanthroline ligand resulting from favourable hydrophobic interactions between the surfactant aggregates and dissociated phenanthroline ligand and solubilisation of the ligand by DPC. Plots of observed pseudo-first-order rate constants against surfactant concentration show maxima, characteristic of many micellar catalyses. Shifts in the position of the maxima and the values of the aquation rates in the presence of other ions may be due to changes in the critical micelle concentration and the presence of submicellar aggregates. Additional rate enhancement is observed in the presence of sodium benzoate. In addition, complex kinetic behaviour is observed under these conditions. Additional pathways for complex and/or ligand binding may be responsible for these.