IRON-OXIDE COLLOIDS AND T-BUTYLHYDROPEROXIDE IN REVERSE MICROEMULSIONS - A NEW AND EFFICIENT SYSTEM FOR CARBON-HYDROGEN BOND ACTIVATION

Iron oxide colloids generated by the hydrolysis of ferric nitrate nona hydrate in Aerosol-OT reverse microemulsions catalyze (after the addit ion of tert-butylhydroperoxide) the functionalization of the hydrocarb ons constituting the continuous phase of these micellar systems. In th e case of cyclooctane, used to set up this new model and in all the pr eliminary studies, the carbon-hydrogen bond activation products are (i n decreasing order) tert-butylperoxycyclooctane, cyclooctene, cyclooct anone and cyclooctanol, under static nitrogen atmosphere and at room t emperature. This reaction is very sensitive to temperature variations and dioxygen partial pressure. Cycloalkane tert-butylperoxidation rema ins the major process at 50 degrees C under anaerobic conditions and m akes this procedure an interesting alternative to other methods alread y described in the literature. The evolvement of cyclooctane oxidation into an autooxidation reaction in the presence of molecular oxygen an d model extension experiments to other substrates gave the following s equence of regioselectivity: 3 degrees>2 degrees much greater than>11 degrees, in agreement with an homolytic cleavage of C-H bonds. The nat ure of the active species in such a dispersed medium is discussed on t he basis of recently published results dealing with the influence of s olvent polarity on tBHP decomposition.