Highly Efficient Synthesis of Alkyl Levulinates from α-Angelica Lactone, Catalyzed with Lewis Acidic Trifloaluminate Ionic Liquids Supported on Carbon Nanotubes

Abstract

Levulinic acid esters (LAEs) were synthesised from -angelica lactone and alcohols, in a reaction catalysed by a new family of chloride-free Lewis acidic ionic liquids, containing trifloaluminate anions, [Al(OTf)3+n] n-. Changing the catalyst from poorly soluble Al(OTf)3 (used as suspension) to fully homogenous trifloaluminate ionic liquids resulted in shorter reaction times required for full α-AL conversion (60 min at 60 °C for 0.1 mol% catalyst loading), and unprecedented selectivities to LAEs, reaching >99%. Supporting the trifloaluminate ionic liquid on multi-walled carbon nanotubes gave an easily-recyclable system, with no leaching observed over 6 cycles. Mechanistic considerations suggest that the propensity of Al(OTf)3 to undergo very slow hydrolysis results in the correct balance of Brønsted and Lewis acidic sites in the system, inhibiting by-product formation.

Recent Advances in the Value Addition of Biomass‐Derived Levulinic Acid: A Review Focusing on its Chemical Reactivity Patterns

“…As evident from Table 1, EL can be prepared in excellent yields from feedstock like LA, AGL, and FAL. [27,[71][72][73][74][75]78] Both homogeneous and heterogeneous catalysts have been very effective for esterification or alcoholysis reactions. The reactions generally require elevated temperature and excess ethanol.…”

“…[26] A classic example of the chemocatalytic conversion of biomass is the acid-catalyzed depolymerization, hydrolysis, and dehydration of biomass-derived carbohydrates into furanics and levulinates such as 5-(hydroxymethyl)furfural (HMF), furfural (FUR), and levulinic acid (LA) (Scheme 1). [27,28] HMF is formed by the sequential elimination of three molecules of water from hexose sugars like glucose under acid catalysis. [29] The process allows a 50 % reduction of oxygen content in the parent sugar molecule without undergoing any CÀ C bond scission reaction.…”

PTFE-Carbon Nanotubes and Lipase B from Candida antarctica—Long-Lasting Marriage for Ultra-Fast and Fully Selective Synthesis of Levulinate Esters

“…LAEs can be obtained directly from polysaccharides at a high temperature (175 °C) [ 4 ] or from furfuryl alcohol at 120−140 °C, in the presence of sulfonated materials [ 4 ], or acidic ionic liquids [ 5 ]. Another known method is the catalytic one-pot upgrading of α-angelica lactone (5-methyl-2(3 H )-furanone, α-AL) in the presence of an acidic catalyst [ 6 , 7 , 8 ] at 60 °C or via biotransformation at ambient temperature [ 9 ].…”

Highly Active Trifloaluminate Ionic Liquids as Recyclable Catalysts for Green Oxidation of 2,3,6-Trimethylphenol to Trimethyl-1,4-Benzoquinone

“…Searching for halogen-free and water-stable Lewis acidic catalysts for organic synthesis, in our previous work, new acidic trifloaluminate ionic liquids were presented [19,20]. Trifloaluminate ionic liquids were synthesised in analogy to chlorometallate systems [21] with the difference that instead of the chlorido ligands on Al atoms, trifluoromethanesulfonate (triflate, OTf) ligands were present.…”

“…The oligonuclear anionic complexes having various triflate bridging modes were postulated to create anions. The catalytic performance of these systems as acidic catalysts was presented in the synthesis of chromanes [19] and alkyl levulinates [20].…”