Consequences of altering acid strength in MFI zeolites via phosphorus modification on Friedel-Crafts acylation

Friedel-Crafts acylation is an important reaction for the formation of C[sbnd]C bonds to produce a variety of commodity chemicals. Recent efforts have been made to reduce the environmental footprint of these reactions by utilizing renewable carboxylic acids directly (rather than halogenated species), using renewable acyl acceptors, and using zeolites as non-sacrificial catalysts. While the direct conversion of acids to valuable products is appealing, the role of acid strength and local environment on rates and stability for this reaction is unknown. Here we report the acylation of 2-methylfuran with acetic acid over phosphorus-modified MFI zeolites with various phosphorus loadings. We show that while P modification increases observed activation barriers for acylation when compared with traditional Bronsted sites, net rates of reaction can be increased. Further, selectivity is improved by reduced rates of acid self-coupling side reactions to a greater extent. Importantly, the phosphorus-modified samples also exhibit slower coke formation, and therefore deactivation, due to diminished side reactions.