(741d) Friedel-Crafts Acylation of Lignin-Derived Compounds with Acetic Acid on Brønsted Zeolites

Acetic acid, which is one of the most abundant oxygenates present from biomass thermal decomposition, was found to generate acylium ion intermediates that can be used to directly acylate a variety of biomass derived species [1,2] to generate fuels and high-value chemicals.

In this study, activation barriers and mass transfer limitation for Friedel-Crafts acylation reactions between acetic acid and a variety of biomass- and petroleum-derived acyl acceptors are evaluated. The rate determining step can shift from acyl formation in methylfuran acylation [3] to C-C coupling in the presence of weaker acyl acceptors such as toluene. The C-C coupling is also rate determining step for the self-acylation reaction. In addition, it is observed that the acylation rate can be higher or lower as the acyl acceptor is varied. We show how apparent activation energy for furan and m-cresol acylation is lower than that for ketonization, whereas the apparent energy barrier for toluene acylation is higher than that for ketonization.

The effect water, which is always present during biomass processing, has been investigated in this study. It was found that water inhibits the reaction but also helps improving catalyst stability during acylation [1,3].

We further illustrate the important influence of mass transfer and confinement effects within the zeolites. We find that many of the discrepancies reported in the literature are simply due to improper accounting for diffusion limitation. Finally, we reveal the intriguing chemistry associated with alcohol containing acyl acceptors, and how the intermediate esters formed can play a critical role on overall acylation rates.

References

1. Gumidyala, A., Sooknoi, T., Crossley, S., Journal of Catalysis 340 (2016) 76–84.

2. Pham, T. N., Sooknoi, T., Crossley, S. P., & Resasco, D. E., ACS Catal. 2013, 3, 2456−2473

3. Gumidyala, A., Wang B., and Crossley, S., Science Advances, 2 (9), e1601072, (2016)