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A unique strategy for the formation of furan-2,5-dicarboxylic acid (FDCA)-derived esters with methanol and ethylene glycol in concentrated solutions was reported using a six-membered ring acetal of (5-hydroxymethyl)­furfural (HMF) with 1,3-propanediol in order to improve the economics for the production of polyethylene 2,5-furandicarboxylate (PEF), a biobased polyester. Aerobic oxidative esterification with methanol and ethylene glycol in the presence of a CeO2-supported Au catalyst gave 80–95% yields of methyl furan-2,5-dicarboxylate and bis­(2-hydroxyethyl)­furan-2,5-dicarboxylate from concentrated HMF-acetal solutions (10–20 wt %). Kinetic studies combined with density functional theory (DFT) calculations were used to identify two key steps for the conversion of the cyclic acetal ring to the corresponding methyl ester: (i) partial hydrolysis of the acetal ring by OH– ions and (ii) subsequent oxidation of the hemiacetal in solution by molecular O2 on Au nanoparticles. These results represent a significant contribution not only to cutting-edge conversion technology for renewable biomass feedstocks to PEF-based applications but also to opportunities for the efficient conversion of substrates with a reactive formyl group in high yield.

The N2 ligand in the title complex (M8[16]anS4 = 3,3,7,7,11,11,15,15‐octamethyl‐1,5,9,13‐tetrathiacyclohexadecane) displays unprecedented reactivity. It reacts with aryl halides and benzyl bromide in toluene at room temperature without irradiation to give MoII aryldiazenido and dibenzylhydrazido complexes, respectively. Its reaction with methanol and acetone affords NH3 and Me2CNNCMe2, respectively. Phosphane analogues of the title complex do not undergo such reactions. The structure of trans [MoI(N2‐p‐C6H4CO2Me)(Me8[16]anS4)], the diazenido complex, is shown on the right.

A novel catalytic strategy involving protective chemistry is presented for the selective production of 5-formylfuran-2carboxylic acid (FFCA) and furan-2,5-dicarboxylic acid (FDCA) from concentrated 5-hydroxymethylfurfural (HMF) solutions. By protecting the reactive formyl group of HMF by acetalization with 1,3-propanediol (PDO), degradation and premature oxidation of HMF is suppressed. A hydroxyapatite-supported Au catalyst can selectively oxidize HMF-acetal in a 10 wt % solution to FFCA-acetal in 94 % yield in 2 hours at 373 K under 0.5 MPa of O 2 . Deprotection of FFCA-acetal by mineral acids affords FFCA in 98 % yield and recovers nearly all PDO. FFCA in a 20 wt % solution can be oxidized to FDCA in 95 % yield under similar reaction conditions. The presented chemistry contributes to the development of novel manufacturing routes of prospective biobased monomer precursors using protecting agents.

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