New approaches for obtaining renewable naphthalenes by acid-catalyzed Diels-Alder additions: The role of furan-aromatic condensations

Abstract

This study demonstrates the feasibility of producing naphthalenes from renewable sources, specifically furans, olefins, and alcohols. Screening of various zeolites at 500 ºC, 0.2 MPa, with a 1:1 furan ratio and a WHSV of 0.69 h⁻¹ identified MFI (ZSM-5) as the most effective catalyst. Our findings indicate that reactions between furan and alkylated monoaromatics result in lower naphthalene yields with increased aromatic ring alkylation, attributed to steric hindrance and increased electron density from alkyl groups, which interfere with key Diels-Alder reactions. Notably, substituting furan with furfural doubled the naphthalene yield to 20.2 %. Although replacing olefins with alcohols did not significantly alter yields, it improved the process's sustainability by employing bioplatform molecules. We also suggest recycling the large quantity of monoaromatics produced during the reaction, which, after separation, led to a maximum naphthalene yield of 27.4 % and sustained catalytic activity over time.