Theoretical study of the catalytic oxidation mechanism of 5-hydroxymethylfurfural to 2,5-diformylfuran by PMo-containing Keggin heteropolyacid

• Published in: Catalysis science & technology Vol. 6; no. 11; pp. 3776 - 3787
• Main Authors: Ren, Li-Ke, Yang, Hua-Qing, Hu, Chang-Wei
• Format: Journal Article
• Language: English
• Published: 01.01.2016
• Subjects: Bonding; Catalysis; Catalysts; Cleavage; Fracture mechanics; Methylene; Oxidation; Peroxides
• ISSN: 2044-4753; 2044-4761
• DOI: 10.1039/C5CY01895A

The mechanism for the aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) catalysed by PMo-containing Keggin heteropolyacid (H 3 PMo 12 O 40 ) has been systematically investigated at the M06/6-31++G(d,p), Lanl2dz level in dimethylsulfoxide. For H 3 PMo 12 O 40 in dimethylsulfoxide, the most stable species was [PMo 12 O 40 ] 3− , which was the catalytic active species for the aerobic oxidation of HMF to DFF. Over the [PMo 12 O 40 ] 3− active species, the reaction of 2HMF + O 2 → 2DFF + 2H 2 O was associated with three successive reaction stages: the oxidation of the first HMF to DFF by [PMo 12 O 40 ] 3− , the import of O 2 to form the peroxide [PMo 12 O 41 ] 3− and the oxidation of the second HMF to DFF by [PMo 12 O 41 ] 3− , regenerating [PMo 12 O 40 ] 3− . The oxidation of each HMF involves two main reaction steps: the cleavage of the O–H bond in the hydroxyl group and cleavage of the C–H bond in the methylene group of HMF. The turnover frequency determining the transition state was the first-step C–H bond cleavage in the methylene group of HMF with a rate constant of k H = 1.345 × 10 8  exp(−153 476/ RT ), while the turnover frequency determining the intermediate was representative of the HMF-containing molecular complex on [PMo 12 O 40 ] 3− . The value of the kinetic isotope effects ( k H / k D ) is predicted to be about 4.2–5.9 over the temperature range 373–433 K. This study provides an insight into the catalytically crucial step in the oxidation of HMF to DFF.