Acidic ionic liquid catalyzed liquefaction of cellulose in ethylene glycol; Identification of a new cellulose derived cyclopentenone derivative

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Cellulose can be liquefied in ethylene glycol at 180 °C, using 6.7 mol % 1-(1-alkylsulfonic)-3-methylimidazolium chloride ionic liquids as catalysts. The maximum liquefied product yields of 0.3436 and 0.3046 g/g of cellulose were achieved after 20 h at 180 °C using 1-(1-proylsulfonic)-3-methylimidazolium chloride and 1-(1-butylsulfonic)-3-methylimidazolium chloride as the catalysts. The liquefied oil produced from both ionic liquid catalysts had similar compositions. Unlike in previously reported mineral acid catalyzed cellulose liquefactions, the new catalysts give stable oils with well-defined compositions of only three compounds. The three compounds in the oil were identified as 2-hydroxyethyl levulinate, 2-hydroxyethyl levulinate ethylene ketal, and 2,3,6,7-tetrahydro-cyclopenta[1,4]dioxin-5-one using GC-MS, HRMS, and 1H, 13C, and 1H-1H COSY NMR spectroscopy. The third product 2,3,6,7-tetrahydro-cyclopenta[1,4]dioxin-5-one is a new C-6 carbohydrate derived cyclopentenone derivative, identified for the first time in a cellulose liquefaction process. The composition of the three components reaches a steady state after 20 h of reaction at 180 °C with a 2-hydroxyethyl levulinate:2-hydroxyethyl levulinate ethylene ketal:2,3,6,7-tetrahydro-cyclopenta[1,4]dioxin-5-one molar percentage ratio of approximately 47:22:31.

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