Bronsted-acidic ionic liquids as efficient catalysts for the synthesis of polyoxymethylene dialkyl ethers

Acetalation of formaldehyde (HCHO) with dialkyl formal or aliphatic alcohol to prepare polyoxymethylene dialkyl ethers (RO(CH2O)(n)R, n >= 1) catalyzed by Bronsted-acidic ionic liquids has been developed. The correlation between the structure and acidity activity of various ionic liquids was studied. Among the ionic liquids investigated, 1-(4-sulfonic acid)buty1-3-methylimidazolium hydrogen sulfate ([MIMBs]HSO4) exhibited the best catalytic performance in the reaction of diethoxymethane (DEM1) with trioxane. The influences of ionic liquid loading, molar ratio of DEM1 to HCHO, reaction temperature, pressure, time, and reactant source on the catalytic reaction were explored using [MIMBs]HSO4 as the catalyst. Under the optimal conditions of n(NIMBsJHSO(4)):n(DEM1):n(HCHO) = 1:80:80, 140 degrees C, and 4 h, the conversion of HCHO and selectivity for DEM2-8 were 92.6% and 95.1%, respectively. The [MIMBs]HSO4 catalyst could be easily separated and reused. A feasible mechanism for the catalytic performance of [MIMBs]HSO4 was proposed. (C) 2017, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.