Effect of small concentrations of water on ethylbenzene oxidation with molecular oxygen catalyzed by iron(II, III) acetylacetonate complexes with 18-crown-6

Abstract

The catalytic effects of small amounts of water (∼10−3 mol/l) added to the ethylbenzene oxidation reaction with molecular oxygen catalyzed by the system {Fe(III)(acac)3 + 18-crown-6 (18C6)} were revealed. An increase in the reaction rate was observed, and the direction of the oxidation reaction changed. In the presence of the catalytic system {Fe(III)(acac)3 (5.0 × 10−3 mol/l) + 18C6 (5.0 × 10−3 mol/l) + H2O (3.7 × 10−3 mol/l}, the main product at early stages of ethylbenzene oxidation is acetophenone, rather than α-phenylethyl hydroperoxide produced in the case of catalysis by the system {Fe(III)(acac)3 (5.0 × 10−3 mol/l) + 18C6 (5.0 × 10−3 mol/l)} (in the absence of water admixture). A method is proposed to evaluate the activity of forming in situ (Fe(II)(acac)2)x(18C6)y(H2O)n complexes at microstages of chain initiation (O2 activation) and propagation (Ct+RO2·) involving the catalyst, which determine the rate and selectivity of oxidation. A possible “dioxygenase-like” mechanism of conversion of iron complexes with 18C6 in the presence of activating H2O admixtures is discussed.