Kinetics and mechanism of anthracene oxidation with tert-butyl hydroperoxide over metal-organic frameworks Cr-MIL-101 and Cr-MIL-100

• Kinetic of anthracene oxidation with TBHP over MIL-101(100) has been studied.
• The reaction is zero order in substrate and first order in both oxidant and catalyst.
• The activation energy is similar for MIL-101 and MIL-100.
• The oxidation process is not controlled by diffusion of the reactants.
• The rate-limiting step is interaction of TBHP with Cr(III) centers of MIL-101(100).

The oxidation of anthracene (AN) with tert-butyl hydroperoxide (TBHP) over metal-organic frameworks (MOFs) Cr-MIL-101 and Cr-MIL-100 produced anthraquinone (AQ) in a nearly quantitative (>99%) yield after 1 and 4 h, respectively, at 100 °C in chlorobenzene (ClPh). At initial stages of the reaction, some amounts (<13%) of intermediate products, anthrahydroquinone and oxanthrone, were detected along with traces of 9-hydroxyanthracene and/or anthrone. Kinetic study revealed that the oxidation reaction is unaffected by the presence of molecular oxygen and is zero order in AN and first order in both TBHP and MOF catalyst. Additives of radical chain scavengers produced no effect on the reaction rate and selectivity. The activation energy Ea was found to be similar for MIL-101 and MIL-100 (15 kcal/mol) while pre-exponential factors were different (7·106 and 3·106 L/(mol·min), respectively). The kinetic results indicated that the AN oxidation with TBHP over both MIL-101 and MIL-100 is not controlled by diffusion. No adsorption of AN on the MOFs from ClPh solution was found at the reaction temperature. A mechanism that involves a reversible interaction between TBHP and CrIII centers within the MOF framework producing an active oxidizing species (rate-limiting step), followed by oxygen atom transfer from the peroxo species to the aromatic substrate to give primary oxygenated product(s), further oxidation of which leads to AQ, has been suggested.

The kinetic and adsorption studies revealed that anthracene oxidation with TBHP over Metal-Organic Frameworks MIL-100 and MIL-101 is not controlled by diffusion. The rate-limiting step of the reaction is interaction of the oxidant with CrIII centers.Figure optionsDownload as PowerPoint slide