Synthesis and Characterization of Oligomeric Ionic Liquid/Heteropoly Acid Composite as a New Heterogeneous Catalyst through Anion-Exchange Method for Selective Cyclohexane Oxidation with Molecular Oxygen under Solvent-Free Conditions

Abstract

In this work, we investigated solvent-free oxidation of cyclohexane using oligomeric ionic liquid (OIL)/heteropoly acid (HPA) composite with molecular oxygen under solvent-free conditions. OIL has six imidazolium cores which synthesized in three successive stages and was anion-exchanged by phosphomolybdic acid (H3PMo12O40, PMo) to synthesize OIL/HPA composite. OIL and OIL/HPA composite were characterized by different techniques such as, FT-IR, UV, BET, TGA, XRD, FESEM, EDX, and TEM. Optimal reaction conditions were obtained by evaluating the effective parameters on the reaction including temperature, time, oxygen pressure, and amount of the catalyst. The main product of the reaction in the presence of 20 mg of catalyst and 5 mL of cyclohexane was cyclohexanone by 21% conversion and 75% selectivity at 110 °C and 20 bar oxygen pressure after 5 h. The OIL/HPA showed good stability under reaction conditions and maintained its catalytic activity up to five cycles with little decrease in reaction conversion.

Ionic Liquids in Metal, Photo-, Electro-, and (Bio) Catalysis

“…1543 Oligomeric ILs (OILs) contain-ing six Im cores associated with phosphomolybdic anion catalyze the oxidation of cyclohexane to cyclohexanone in moderate yields. 1544 Ethylbenzene oxidation with oxygen was reported by SiO 2 1545 or PS 1546 coated with CoCl 2 dissolved in various ILs but with relative low conversion. Similarly the oxidation of ethylbenzene to acetophenone was accomplished by CNT functionalized with Cu(II) and coated with ILs.…”

“…There is a synergetic effect on the oxidation of benzylic C–H bonds by Ni-MOF and [C 4 C 1 Im]­[Br] using tert -butyl hydroperoxide as oxidant . Oligomeric ILs (OILs) containing six Im cores associated with phosphomolybdic anion catalyze the oxidation of cyclohexane to cyclohexanone in moderate yields …”

Selective vapor‐phase oxidation of o‐xylene to phthalic anhydride over Co‐Mn/H3PW12O40@TiO2 using molecular oxygen as a green oxidant

“…Therefore, in a homogeneous reaction the isolation of the products and the reuse of the catalyst after reaction become difficult . Several studies were published on the heterogenization and immobilization of HPAs on various supports and their use in catalysis as green catalysts . Accordingly, this is an attractive strategy to improve the ease of separation, increasing surface area, and catalyst reusability.…”

“…[10] Several studies were published on the heterogenization and immobilization of HPAs on various supports and their use in catalysis as green catalysts. [11][12][13] Accordingly, this is an attractive strategy to improve the ease of separation, increasing surface area, and catalyst reusability. Since physically adsorbed HPW on the support surface can leach out easily, encapsulation of these catalysts onto the porous material might be the most effective approach.…”