Effect of 4,4′-dialkyl-2,2′-bipyridine ligands on the hydrolysis of dichlorodioxomolybdenum(VI) catalyst precursors and the switch from homogeneous epoxidation to heterogeneous systems

abstract

Molybdenum catalysts have been industrially recognized for decades for liquid phase epoxidation, which is an important chemical reaction process, since epoxides are used for many industrial applications. In this work, molybdenum oxide hybrid catalysts, prepared by a reflux hydrolysis methodology, performed effectively as heterogeneous catalysts or reaction-induced self-separating catalysts under mild reaction conditions; in the two cases, the catalyst separation and reuse are facilitated. Specifically, catalysts with the general formula [MoO3(L)], possessing polymeric chain-like (L = 4,4 '-dimethyl-2,2 '-bipyridine (1)) or oligomeric (L = 4,4 '-dinonyl-2,2 ' bipyridine (2)) structures comprising corner-sharing {MoO4N2} units, were synthesized and characterized by various complementary techniques (ATR FT-IR, Raman, 13C{1H} CP MAS NMR spectroscopy, PXRD, SEM, TGA, elemental analysis, ICP-OES and N2 sorption isotherms). Small chemical differences in the organic synthesis precursor had important structure directing effects on the type of hybrid material formed. The hybrids promoted olefin epoxidation with H2O2 or tert-butylhydroperoxide (TBHP) as oxidant. For example, 1 catalyzed the conversion of biobased olefins (70 degrees C) and lignin-based isoeugenol (50 degrees C) with TBHP to useful bioproducts, in heterogeneous phase, leading to an epoxide yield of 100 % for DL-limonene (3:1 M molar ratio of 1,2-epoxy-pmenth-8-ene to 1,2:8,9-diepoxy-p-menthane), 81 % epoxide yield for fatty acid methyl esters, and 80 % Licarin A selectivity at 40 % isoeugenol conversion. For dienes (DL-limonene, methyl linoleate), kinetic modelling studies suggested that the formation of the monoepoxides was faster than that of diepoxides, accounting for enhanced monoepoxide selectivity.

keywords

ACID METHYL-ESTERS; OLEFIN EPOXIDATION; STRUCTURAL ELUCIDATION; HYDROTHERMAL SYNTHESIS; SELECTIVE EPOXIDATION; MOLYBDENUM COMPLEXES; MESOPOROUS MATERIALS; PEROXO COMPLEXES; HYBRID MATERIALS; VEGETABLE-OILS

subject category

Chemistry; Engineering

authors

Gomes, DM; Gomes, AC; Neves, P; Paz, FAA; Valente, AA; Gonçalves, IS; Pillinger, M

Groups

G1 - Porous Materials and Nanosystems
G4 - Renewable Materials and Circular Economy

Projects

CICECO - Aveiro Institute of Materials (UIDB/50011/2020)

CICECO - Aveiro Institute of Materials (UIDP/50011/2020)

Associated Laboratory CICECO-Aveiro Institute of Materials (LA/P/0006/2020)

Rede Nacional de Ressonância Magnética Nuclear (PTNMR)

acknowledgements

The authors are grateful to Maria do Rosario Teixeira Soares (Central Laboratory of Analysis, University of Aveiro) for assistance with the acquisition of powder X-ray diffraction data. The work in this paper was developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 (DOI 10.54499/UIDB/50011/2020) , UIDP/50011/2020 (DOI 10.54499/UIDP/50011/2020) & LA/P/0006/2020 (DOI 10.54499/LA/P/0006/2020) , financed by National funds through the FCT (Fundacao para a Ciencia e a Tecnologia) /MCTES (Ministerio da Ciencia, Tecnologia e Ensino Superior) (PIDDAC) . D.M.G. (grant ref. 2021.04756.BD) is grateful to the FCT for a PhD grant (State Budget, European Social Fund (ESF) within the framework of PORTUGAL2020, namely through the Centro 2020 Regional Operational Program) . A.C.G. acknowledges the FCT/MCTES for an Assistant Researcher Position funded through the Individual Call to Scientific Employment Stimulus (ref. CEECIND/02128/2017; DOI 10.54499/CEECIND/02128/2017/CP1459/CT0039) . The NMR spectrometers used in this work are part of the National NMR Network (PTNMR) and are partially supported by Infrastructure Project N degrees 022161 (co-financed by FEDER through COMPETE 2020, POCI and PORL, and FCT through PIDDAC) .