Study of Ligand Substitution Reactions Involving the Fe(CN)5H2O3- Ions in Surfactant Solutions

Abstract

The reaction of Fe(CN) s H 2 0 3- and pyridine was studied in aqueous electrolyte solutions (NaCl0 4 , LiCl0 4 , Mg(CI0 4 ) 2 , and SdCl0 4 ) 2 ) along with sodium dodecyl sulfate, SDS, cetyltrimethylammonium bromide, CTAB, and octylphenoxy polyethoxyethanol Triton X-100, aqueous solutions. Surfactant concentration changes do not influence the reaction rate in the nonionic surfactant solutions. In SDS solutions, an unexpected dependence of the observed rate constant on [SDS] is found. The observed rate constant is affected by [CTAB] changes not only in the surfactant concentration range above the cmc but also for [CTAB] cmc. To rationalize the dependence of the reaction rate on [CTAB], two different models were used. In the premicellar surfactant concentration range a simple stepwise self-association model was used, and in the postmicellar surfactant concentration range a simple mass action model was used. To give support to the treatment of the kinetic data presented, the same two models were also used to explain kinetic data for the related substitution reaction of Fe(CN) 5 H 2 O 3- and pyrazine in CTAB solutions. With the idea of investigating the influence of the charge of the entering ligand on the kinetic micellar effects on dissociative substitution reactions involving aquopentacyanoferrate(II) species, kinetic data for the process Fe(CN) 5 H 2 O 3- and Co(en) 2 (pzCO 2 ) 2+ were also considered.