Recent progress in metabolic engineering has generated new microorganisms able to convert carbohydrates and waste lignin into biopriviledged molecules.¹ One of these molecules, muconic acid, can be further diversified to adipic acid and terephthalic acid, which are central to the production of Nylon-6,6 and polyethylene terephthalate (PET). Its semi-hydrogenation also leads to new molecules such as trans-3-hexenedioic acid (3HDA), a compound that enables the synthesis of bio-advantaged Nylon-6,6. However, to achieve economically sustainable conversion, it is crucial to streamline the fermentation and downstream catalytic processing steps. This generates new challenges as biogenic impurities inherent to the fermentation broth can deactivate Pt-group metal catalysts.

An alternative approach would be to utilize novel conversion schemes using robust base metals that are stable in the presence of biogenic impurities.² We show that electrosynthesis represents a promising approach for the direct processing of unpurified broths.^2,3 The water, salts, and acidic impurities already present in the medium provide a suitable electrolyte, while protons in the solution provide the hydrogen required for the desired transformation. Muconic acid was converted to 3HDA with a 94% yield and 100% faradaic efficiency using lead (Pb) electrodes.⁴ Under these conditions, 3HDA can be produced at a competitive price of $2.00 kg^-1. The reaction mechanism and the origin of the high selectivity to 3HDA will be discussed.

1. B.H. Shanks and P. Keeling, Bioprivileged Molecules: Creating Value from Biomass, Green Chem. 2017, advance article. https://dx.doi.org/10.1039/C7GC00296C

2. M. Suastegui, J. E. Matthiesen, J. M. Carraher, N. Hernandez, N. Rodriguez Quiroz, A. Okerlund, E. W. Cochran, Z. Shao, J.-P. Tessonnier, Combining Metabolic Engineering and Electrocatalysis: Application to the Production of Polyamides from Sugar, Angew. Chem. Int. Ed., 2016, 55, 2368-2373. http://dx.doi.org/10.1002/anie.201509653

3. J. E. Matthiesen, J. M. Carraher, M. Vasiliu, D. A. Dixon, J.-P. Tessonnier, Electrochemical Conversion of Muconic Acid to Biobased Diacid Monomers, ACS Sustainable Chem. Eng., 2016, 4, 3575-3585. http://dx.doi.org/10.1021/acssuschemeng.6b00679

4. J. E. Matthiesen, M. Suástegui, Y. Wu, M. Viswanathan, Y. Qu, M. Cao, N. Rodriguez-Quiroz, A. Okerlund, G. Kraus, D. R. Raman, Z. Shao, J.-P. Tessonnier, Electrochemical Conversion of Biologically Produced Muconic Acid: Key Considerations for Scale-up and Corresponding Technoeconomic Analysis, ACS Sustainable Chem. Eng., 2016, 12, 7098-7109. http://dx.doi.org/10.1021/acssuschemeng.6b01981