KINETIC-STUDY OF THE IRON(III) OXIDATION OF SOME ALKYL-SUBSTITUTED FERROCENES IN WATER-IN-OIL MICROEMULSIONS OF AOT IN HEPTANE, ISOOCTANE AND DECANE

The kinetics of iron(III) oxidation of ferrocene and its 1,1'-dimethyl and 1,1'-dibutyl derivatives have been investigated at 20.0 degrees C in oil-AOT-water microemulsions by changing the organic solvent (hept ane, isooctane and decane) and the molar ratio R = [H2O](ov)/[AOT](ov) in the range 9.0-25.0, the overall AOT surfactant concentration being kept constant at 0.13 mol dm(-3). In all cases studied the reaction r ate decreases with increasing the parameter R and the overall rate con stants are always smaller than those for the corresponding reactions i n homogeneous aqueous solution. The kinetic data, interpreted by apply ing the pseudophase model to the microemulsions, indicate that the oxi dation reaction takes place in the water pools and at the surfactant/w ater interface. The kinetic results allow the evaluation of the partit ion coefficients of the substrates between the oil and the aqueous pha ses. For a given oil, these partition coefficients increase as the red ucing substrate becomes increasingly hydrophobic. The estimated increm ental free energies of transfer of a methylene (or methyl) group of th e substrate from water pools to the oils are independent of the type o f the organic solvent used.