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We report on the synthesis and characterization of novel mesoporous chiral polyboronates obtained by condensation of ( R , S )/( S , S )-hexane-1,2,5,6-tetrol (HT) with simple aromatic diboronic acids (e.g., 1,3-benzenediboronic acid) (BDB). HT is a cellulose-derived building block comprising two 1,2-diol structures linked by a flexible ethane bridge. It typically consists of two diastereomers one of which [( S , R )-HT] can be made chirally pure. Boronic acids are abundantly available due to their importance in Suzuki–Miyaura coupling reactions. They are generally considered nontoxic and easy to synthesize. Reactive dissolution of generally sparingly soluble HT with BDB, in only a small amount of solvent, yields the mesoporous HT/polyboronate materials by spontaneous precipitation from the reaction mixture. The 3D nature of HT/polyboronate materials results from the entanglement of individual 1D polymeric chains. The obtained BET surface areas (SAs) and pore volumes (PVs) depend strongly on HT’s diastereomeric excess and the meta/para orientation of the boronic acids on the phenyl ring. This suggests a strong influence of the curvature(s) of the 1D polymeric chains on the final materials’ properties. Maximum SA and PV values are respectively 90 m 2 g –1 and 0.44 mL g –1 . Variably sized mesopores, spanning mainly the 5–50 nm range, are evidenced. The obtained pore volumes rival the ones of some covalent organic frameworks (COFs), yet they are obtained in a less expensive and more benign fashion. Moreover, currently no COFs have been reported with pore diameters in excess of 5 nm. In addition, chiral boron-based COFs have presently not been reported. Scanning electron microscopy reveals the presence of micrometer-sized particles, consisting of aggregates of plates, forming channels and cell-like structures. X-ray diffraction shows the crystalline nature of the material, which depends on the nature of the aromatic diboronic acids and, in the specific case of 1,4-benzenediboronic acid, also on the applied diastereomeric excess in HT.

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We have investigated the synthesis of hexane-1,2,5,6-tetrol (hereafter “tetrol”) from aqueous solutions of biomass-derived levoglucosanol (hereafter “Lgol”) using a (10 wt %)­Pt-(10 wt %)­WO x /TiO2 catalyst in both batch and continuous flow reactors. The tetrol selectivity was over 90% with Lgol feed concentrations of 10–30 wt %. Most of the Lgol feed stereochemistry was preserved (notably 91%), with threo-Lgol (hereafter “t-Lgol”) and erythro-Lgol (hereafter “e-Lgol”) converting to (S,S)-tetrol and (S,R)-tetrol, respectively. The rate of Lgol conversion was found to be first-order in the Lgol concentration, suggesting that the catalyst surface is not saturated with Lgol. The measured reaction order for H2 was zero, which is consistent with either a mechanism involving acid-catalyzed irreversible C–O bond cleavage of Lgol followed by metal-catalyzed hydrogenation of reactive intermediates or one where all of the metal sites are saturated with H2. When the reaction was run in a continuous flow reactor, the catalyst exhibited deactivation with increasing time-on-stream but was found partially regenerable with a consecutive calcination and reduction treatment. Deactivation was concluded to be caused mainly by carbon deposition, with some W-leaching from the catalyst in the initial stages of reaction. The here demonstrated understanding of reaction kinetics and catalyst stability could facilitate the development of improved processes to produce hexane-1,2,5,6-tetrol from biomass.

In this work, we explore the catalytic upgrading of ethanol into diesel following an approach based on the initial Guerbet coupling of ethanol followed by etherification. The results presented are...