Selective reduction of carboxylic acid derivatives represents a key path to convert biomass into value-added chemicals and solvents, the latter which has a rapidly growing market [1]. Ethers are desirable because they possess excellent solvency, chemical stability and compatibility with other organic solvents and formulated products. The known methods to synthesize ethers include reactions between alkyl halides and alkoxides; the addition of alcohols to alkenes; and bimolecular dehydration of alcohols. Less common methods involve direct reduction of esters with homogeneous catalysts [2] with costly metal hydride reagents [3]. All of these routes have significant limitations such as the use of strongly acidic or basic conditions which reduce selectivity due to loss by competing elimination reactions; limited scope of compatibily with bio-sourced substrates due to undesired side-reactions; and costly and toxic manufacturing processes.<br/><br/>Here, we propose and demonstrate a distinct and new method to synthesize ethers from esters with solid catalysts. Steady-state rates and product selectivities for competing reaction pathways for a model ester compound were obtained in packed-bed and trickle bed reactors as functions of reactant pressures, temperature, and as functions of ester conversion, which were controlled via the surface residence time. These findings demonstrate the need to consider both primary and secondary reaction pathways within this complex reaction network. These conclusions are supported both by changes in the full product distribution with conversion and other methods. We will discuss how conversion rates depend on reactant concentrations and the reactor temperature, and how the related kinetic parameters differ between distinct catalysts. This work illustrates a new route to produce complex ethers for novel solvents with greater stability in formulations than esters, and consequently, provides a basis for new categories of biosolvents. Patent filings are under progress.<br/><br/>

Reaction pathways, reactive intermediates, and active sites that reduce esters to ethers on solid catalysts

ACS Fall 2020 Virtual Meeting

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