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  • Phase Behavior That Enables Solvent-Free Carbonate-Promoted Furoate Carboxylation. The journal of physical chemistry letters Frankhouser, A. D., Kanan, M. W. 2020: 7544–51

    Abstract

    Solvent-free chemistry has been used to streamline synthesis, reduce waste, and access novel reactivity, but the physical nature of the reaction medium in the absence of solvent is often poorly understood. Here we reveal the phase behavior that enables the solvent-free carboxylation reaction in which carbonate, furan-2-carboxylate (furoate), and CO2 react to form furan-2,5-dicarboxylate (FDCA2-). This transformation has no solution-phase analogue and can be applied to convert lignocellulose into performance-advantaged plastics. Using operando powder X-ray diffraction and thermal analysis to elucidate the temperature- and conversion-dependent phase composition, we find that the reaction medium is a heterogeneous mixture of a ternary eutectic molten phase, solid Cs2CO3, and solid Cs2FDCA. During the reaction, the amounts of molten phase and solid Cs2CO3 diminish as solid Cs2FDCA accumulates. These insights are critical for increasing the scale of furoate carboxylation and provide a framework for guiding the development of other solvent-free transformations.

    View details for DOI 10.1021/acs.jpclett.0c02210

    View details for PubMedID 32812764

  • A closed cycle for esterifying aromatic hydrocarbons with CO2 and alcohol. Nature chemistry Xiao, D. J., Chant, E. D., Frankhouser, A. D., Chen, Y., Yau, A., Washton, N. M., Kanan, M. W. 2019

    Abstract

    The ability to functionalize hydrocarbons with CO2 could create opportunities for high-volume CO2 utilization. However, current methods to form carbon-carbon bonds between hydrocarbons and CO2 require stoichiometric consumption of very resource-intensive reagents to overcome the low reactivity of these substrates. Here, we report a simple semi-continuous cycle that converts aromatic hydrocarbons, CO2 and alcohol into aromatic esters without consumption of stoichiometric reagents. Our strategy centres on the use of solid bases composed of an alkali carbonate (M2CO3, where M+=K+ or Cs+) dispersed over a mesoporous support. Nanoscale confinement disrupts the crystallinity of M2CO3 and engenders strong base reactivity at intermediate temperatures. The overall cycle involves two distinct steps: (1) CO32--promoted C-H carboxylation, in which the hydrocarbon substrate is deprotonated by the supported M2CO3 and reacts with CO2 to form a supported carboxylate (RCO2M); and (2) methylation, in which RCO2M reacts with methanol and CO2 to form an isolable methyl ester with concomitant regeneration of M2CO3.

    View details for DOI 10.1038/s41557-019-0313-y

    View details for PubMedID 31451785