STUDY OF LIGAND SUBSTITUTION-REACTIONS INVOLVING THE FE(CN)(5)H2O3- IONS IN SURFACTANT SOLUTIONS

The reaction of Fe(CN)(5)H2O3- and pyridine was studied in aqueous ele ctrolyte solutions (NaClO4, LiClO4, Mg(ClO4)(2), and Sr(ClO4)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 de pendence of the observed rate constant on [SDS] is found. The observed rate constant is affected by [CTAB] changes not only in the surfactan t concentration range above the cmc but also for [CTAB] < cmc. To rati onalize the dependence of the reaction rate on [CTAB], two different m odels were used. In the premicellar surfactant concentration range a s imple stepwise self-association model was used, and in the postmicella r surfactant concentration range a simple mass action model was used. To give support to the treatment of the kinetic data presented, the sa me two models were also used to explain kinetic data for the related s ubstitution reaction of Fe(CN)(5)H2O3- and pyrazine in CTAB solutions. With the idea of investigating the influence of the charge of the ent ering ligand on the kinetic micellar effects on dissociative substitut ion reactions involving aquopentacyanoferrate(II) species, kinetic dat a for the process Fe(CN)(5)H2O3- and Co(en)(2)(pzCO(2))(2+) were also considered.