Production of 2,6-Naphthalenedicarboxylic Acid from Biomass-Derived Platform Compounds

2,6-Naphthalenedicarboxylic acid (2,6-NDA) is a key monomer for high-performance poly(ethylene naphthalate) (PEN), which is currently produced industrially from petroleum resources via a complex six-step process. Here, a renewable route for the synthesis of 2,6-NDA with an overall yield of 86% from biobased building blocks p-toluquinone and isoprene was developed through a three-step cascade process: (1) a zinc-containing ionic liquid-catalyzed Diels–Alder cycloaddition of methyl-p-benzoquinone and isoprene to construct the dicyclic precursor 2,6-dimethyl-4a,5,8,8a-tetrahydro-1,4naphthoquinone (ProDA), (2) a Cu/SiO2-catalyzed dehydroaromatization-hydrodeoxygenation (DHA-HDO) of ProDA to 2,6-dimethylnaphthalene, and (3) oxidation of 2,6-dimethylnaphthalene using the commercial Co–Mn–Br catalytic system to afford 2,6-naphthalenedicarboxylic acid. In the critical and challenging DHA-HDO step, a copper-phyllosilicate-derived Cu/SiO2 catalyst with adsorption-promotion of Cu0 sites by adjacent Cu+ species plays a key role in the efficient adsorption and transformation of ProDA. This strategy is readily applicable to the synthesis of diverse (multi)methylated naphthalenes, providing a petroleum-independent solution for producing valuable bicyclic aromatic compounds.