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Issue 5, 2018
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Esterification of glycerol and solketal by oxidative NHC-catalysis under heterogeneous batch and flow conditions

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Abstract

The design and synthesis of a set of supported azolium salt pre-catalysts is presented along with their utilization in the production of monoesters of glycerol and solketal by oxidative N-heterocyclic carbene (NHC)-catalysis through batch and continuous-flow approaches. After a propaedeutic study with soluble NHCs, the heterogeneous analogues (silica and polystyrene supports) were tested in a model monoesterification of glycerol using either the Kharasch oxidant or air (in the presence of electron transfer mediators) as the terminal oxidants. The best performing polystyrene-supported triazolium salt pre-catalyst afforded monoacylglycerols (MAGs) in high yields (up to 95%) and almost complete selectivity (monoester/diester >95 : 5) using air and the green solvent Me-THF. The synthesis of fully bio-based MAGs from furfural, 5-hydroxymethylfurfural (HMF), citronellal, and vanillin is also reported. Continuous-flow experiments have been finally performed by fabricating the corresponding packed-bed microreactor, which could be operated for ca. 120 hours with maintenance of conversion efficiency and selectivity.

Graphical abstract: Esterification of glycerol and solketal by oxidative NHC-catalysis under heterogeneous batch and flow conditions

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Publication details

The article was received on 28 Jul 2018, accepted on 18 Sep 2018 and first published on 18 Sep 2018


Article type: Paper
DOI: 10.1039/C8RE00143J
Citation: React. Chem. Eng., 2018,3, 816-825
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    Esterification of glycerol and solketal by oxidative NHC-catalysis under heterogeneous batch and flow conditions

    D. Ragno, A. Brandolese, D. Urbani, G. Di Carmine, C. De Risi, O. Bortolini, P. P. Giovannini and A. Massi, React. Chem. Eng., 2018, 3, 816
    DOI: 10.1039/C8RE00143J

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