Protonic ionic liquids as efficient phase-separation catalysts for esterification of trimethylolpropane and acrylic acid

Abstract

The H 2 SO 4 -based imidazole ionic liquids performed as phase-separation catalysts for the esterification of trimethylolpropane and acrylic acids, exhibiting the best trimethylolpropane conversion (100%) and trimethylolpropane acrylate selectivity (86.4%). • H 2 SO 4 -based ionic liquids were applied as catalysts for esterification of trimethylolpropane and acrylic acid. • A novel phase-separation catalytic process was observed during the reaction. • 100% of trimethylolpropane conversion and 86.4% of trimethylolpropane acrylate selectivity were achieved. • The phase-separated ionic liquids can be steadily reused. Trimethylolpropane acrylate (TMPTA) is becoming an important organic chemistry intermediate, but it’s synthesis through the acid-catalyzed esterification of trimethylolpropane and acrylic acid is a challenge due to the poor activity and catalyst separation problems. In this work, a series of 1,3-propanesultone (PS)-functionalized imidazole ionic liquids (ILs) are prepared and evaluated as the acid catalysts for this reaction, including the catalytic performance comparison, optimization of reaction conditions, and the catalytic reusability. The obtained H 2 SO 4 -based IL ([IMPSH]HSO 4 ) caused a phase-separation catalytic process (reacted as a homogeneous catalyst, but precipitated at the end of reaction like a heterogeneous catalyst), presenting the best trimethylolpropane conversion (100%) and TMPTA selectivity (86.4%). Such catalytic performance is even better than that of homogeneous H 2 SO 4 . Moreover, the catalyst can be steadily reused at least four times without obvious change in activity and its structure. The highly efficient and environmentally benign performance of [IMPSH]HSO 4 -catalyzed esterification of trimethylolpropane and acrylic acid make it possible to achieve industrial applications.