Enhancing the Acylation Activity of Acetic Acid by Formation of an Intermediate Aromatic Ester

5 years ago

Enhancing the Acylation Activity of Acetic Acid by Formation of an Intermediate Aromatic Ester

Steven P. Crossley, Tawan Sooknoi, Bin Wang, Nhung N. Duong, Daniel E. Resasco

Acylation is an effective C−C bond-forming reaction to condense acetic acid and lignin-derived aromatic compounds into acetophenones, valuable precursors to fuels and chemicals. However, acetic acid is intrinsically an ineffective acylating agent. Here, we report that its acylation activity can be greatly enhanced by forming intermediate aromatic esters directly derived from acetic acid and phenolic compounds. Additionally, the acylation reaction was studied in the liquid phase over acid zeolites and was found to happen in two steps: 1) formation of an acylium ion and 2) C−C bond formation between the acylium ion and the aromatic substrate. Each of these steps may be rate-limiting, depending on the type of acylating agent and the aromatic substrate. Oxygen-containing substituents, such as −OH and −OCH3, can activate aromatic substrates for step 2, with −OH> −OCH3, whereas alkyl substituent −R cannot. At the same time, aromatic esters can rearrange to acetophenones by both an intramolecular pathway and, preferentially, an intermolecular one. Be more active: In the acylation reaction of aromatic compounds, acetic acid is not an effective acylating agent. A novel upgrade strategy is proposed that converts acetic acid to aromatic esters, more effective acylating agents, by esterification with Ar−OH. The rate-limiting step of this reaction depends on both the acylating agent and the aromatic substrate. The phenolic derivatives are active towards the acylium ion, whereas the alkylated aromatics are not active.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/cssc.201700394