Affordable and Clean Energy (SDG 7), Responsible Consumption and Production (SDG 12)
Pyrazolyl nickel(II) and palladium(II) complexes as pre-catalysts in the selective hydrogenation of unsaturated compounds and biodiesel Oluwasegun E. Olaoye*, Olayinka Oyetunji 1 , Banothile C. E. Makhubela 2 , Gopendra Kumar 1 and James Darkwa 2,3 1 Department of Chemistry, University of Botswana, Gaborone, Botswana 2 Department of Chemical Sciences, University of Johannesburg, Kingsway Campus, Auckland Park, South Africa 3 Botswana Institute for Technology Research and Innovation, Gaborone, Botswana Environmental impact, high energy demand and depletion of fossil fuels have triggered many reforms to promote the use of alternative sources of energy. Biodiesel from renewable sources offers an attractive alternative to conventional diesel fuel. The selective and/or partial hydrogenation of free-fatty acid methyl esters (FAME) is one of the ways to improve the properties of biodiesel. We have prepared mononuclear pyrazolyl nickel(II) and palladium(II) complexes, by reacting 3,5-dimethyl-1H-pyrazole (L1), 3,5-di-tert-butyl-1H-pyrazole (L 2 ) and 5-ferrocenyl-1H-pyrazole (L3) with [NiBr 2 (DME)] or [PdCl 2 (NCMe) 2 ] to afford [(L1)NiBr 2 ] (1), [(L2)NiBr 2 ] (2), [(L3)NiBr 2 ] (3), [(L1)PdCl 2 ] (4), [(L2)PdCl 2 ] (5) and [(L3)PdCl 2 ] (6), that exhibit significant catalytic activities in the selective and partial hydrogenation of sorbic acid (SA) and methyl linoleate (ML), a typical component of biodiesel. The hydrogenation of SA and ML with the pyrazolyl complexes was followed by 1 H NMR spectroscopy which showed partially hydrogenated intermediate and fully hydrogenated products in the reaction mixture. All the pyrazolyl nickel and palladium complexes were also tested for the hydrogenation of biodiesel produced from chinaberry, melon and jatropha seed oils; and depending on the catalyst and reaction time the product obtained is a blend of un-hydrogenated biodiesel, partially hydrogenated and fully hydrogenated biodiesel. The complexes were active for the partial hydrogenation of biodiesels, thus improving the properties of the biodiesel. Keywords: Pyrazolyl catalysts, Unsaturated compounds, Hydrogenation, Selectivity, Biodiesel
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© The Author(s), 2023
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