Abstract
A series of metal-modified phosphotungstates were prepared and performed for direct synthesis of ethyl levulinate from fructose in ethanol. Considering the cost of catalysts, catalytic activity of catalysts, and easy separation of catalysts together, K-HPW-1 was chosen as the most suitable catalyst for synthesis of ethyl levulinate from fructose. A high ethyl levulinate yield of 64.6 mol% was obtained at 150 °C within 2 h in ethanol. The introduction of low polar toluene as a co-solvent improved the yield of ethyl levulinate to 68.7 mol%. The recovered catalyst remained high activity with the yield of ethyl levulinate converted from fructose above 50 mol% after being used five times. Moreover, the generality of the catalyst was further demonstrated by glucose, sucrose, inulin, and cellulose with ethyl levulinate yielding 14.5, 35.4, 52.3, and 14.8 mol%, respectively.
Highlights
With the gradual diminishment of fossil fuel reserves and increased environmental concerns, it is quite necessary to develop and utilize renewable resources
There is a third route for synthesis of ethyl levulinate that is to be converted from carbohydrates or biomass directly [14,15,16,17]
The yield of ethyl levulinate decreased with K+ instead of H+ in HPW gradually, and this is due to the decrease of Brønsted acidity of potassium phosphotungstates
Summary
With the gradual diminishment of fossil fuel reserves and increased environmental concerns, it is quite necessary to develop and utilize renewable resources. Ethyl levulinate, obtained by esterification of levulinic acid, is a versatile chemical compound and has been widely applied in food industry, as solvents and plasticizers It can be used as an additive for transportation fuels, which shows excellent performance [11,12]. There is a third route for synthesis of ethyl levulinate that is to be converted from carbohydrates or biomass directly [14,15,16,17] This route provides a convenient one-pot reaction to produce ethyl levulinate. Various metal-modified phosphotungstates were prepared to convert ethyl levulinate from fructose in ethanol medium. Among these catalysts, insoluble K-HPW-1 showed highest catalytic activity for direct conversion of fructose into ethyl levulinate with a yield of 64.6 mol%. K-HPW-1 relative to HPW could be facile to separate from reaction mixture by centrifugation and be reused with good catalytic activity
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