Synthesis of Polyoxymethylene Dimethyl Ethers Catalyzed by Pyrrolidinonium-Based Ionic Liquids

Polyoxymethylene dimethyl ethers (PODE n ) are widely applied as diesel additives in engines. Ionic liquids (ILs) replace traditional liquid acids as catalysts in chemical processes. A series of pyrrolidinonium-based Brønsted acidity ILs were synthesized, investigated, and employed as catalysts for the synthesis of PODE n from methylal and trioxane for the first time. The Hammett function values were measured to uncover the connection between catalytic performance and acidity-activity of the ILs considered. The optimal experimental conditions for the synthesis of PODE n were determined. The maximum values of both the conversion of raw material and the selectivity of PODE 3–8 were obtained with 1-octyl-2-pyrrolidinonium trifluoromethanesulfonate ([NOP][TFO]) as the catalyst. [NOP][TFO] provides greater selectivity of PODE 3–4 than the traditional catalysts such as H 2 SO 4 and CF 3 SO 3 H.