Reactions in micellar solutions: Part 14-Kinetics of the reversible complexation of iron(III) with salicylic acid in aqueous anionic and nonionic micellar media

Abstract

The kinetics of the reversible complexation of iron (III) with salicylic acid (H₂Sal) has been investigated at 25.0 ± 0.1°C in aqueous anionic and nonionic micellar media of sodium dodecyl sulphate and triton X 100 respectively. The effect of the nonionic micellar medium is small. In the presence of the anionic micelles, the formation and dissociation of the monosalicylato iron (III) species occur via the reaction:<br><br> <img src='http://www.niscair.res.in/jinfo/equation139.gif' border=0><br><br> where, M denotes micellar pseudophase. There is also evidence for the H⁺ -catalysed aquation of FeSalH<img src='http://www.niscair.res.in/jinfo/equation135.gif' border=0>. The micelles do not alter the intimate mechanism (I_d) for Fe(OH)(OH₂)<img src='http://www.niscair.res.in/jinfo/equation138.gif' border=0> but suppress some of the reaction paths. The protonated complex, FeSalH<img src='http://www.niscair.res.in/jinfo/equation135.gif' border=0>, is kinetically more stable to dissociation in the anionic micellar pseudophase (<em>k</em><img src='http://www.niscair.res.in/jinfo/equation136.gif' border=0>/<em>k</em><img src='http://www.niscair.res.in/jinfo/equation137.gif' border=0> = 0.5 at 25°C) relative to the aqueous medium indicating thereby that the rate limiting process is essentially Fe(III)-ligand bond dissociation.