(495c) Isomerization of Cis,Cis-Muconic Acid for the Sustainable Production of Terephthalic Acid from Biomass

The production of commodity chemicals from cellulosic biomass represents a key step in the transition from fossil to renewable carbon feedstocks. In 2004, the US Department of Energy published a list of the “top 10” bio-based platform chemicals that will be instrumental to the emergence of a sustainable chemical industry. This list has since then been revisited several times [1] and it is now well-accepted that other platform chemicals may emerge in the future. For example, muconic acid is a precursor for the production of adipic acid, hexamethylenediamine, 1,6-hexanediol, caprolactam, and terephthalic acid, which all find important applications in the polymer industry.

Cellulosic glucose is converted to muconic acid using a single fermentative step. Microorganisms have recently been metabolically engineered to achieve economically-relevant yields and titer. However, these microorganisms are highly selective to cis,cis-muconic acid (ccMA). In some instances, other isomers are required. Notably, terephthalic acid is obtained through Diels-Alder reaction between trans,trans-muconic acid (ttMA) and acetylene [2]. The isomerization of ccMA to ttMA, however, is not straight forward. Formation of lactones without observation of ttMA is commonly reported. Only a few methods like refluxing in the presence of I₂ have been successful to isomerize ccMA into ttMA.

The goal of the present work was to understand the isomerization/lactonization mechanisms through kinetic study. A clear understanding of isomerization and lactonization allows for synthesis of catalyst designed specifically to block lactone formation while promoting isomerization to ttMA. It is clear from this study that the electronic configuration of MA isomers can be significantly altered through variation of the protonation state (adjustment of pH and/or introduction of species with high affinity for carboxylate functionality). As a result, high yields of ttMA were achieved through careful control of the reaction conditions. In addition, novel heterogeneous isomerization catalysts that are stable in water at high temperatures for long periods of time were designed.

[1]  Bozell, J. J.; Petersen, G. R.; Technology Development for the Production of Biobased Products from Biorefinery Carbohydrates-the US Department of Energy's "Top 10" Revisited, Green Chem. 2010, 12, 539-554.  http://dx.doi.org/10.1039/B922014C

[2]  Burk, M. J.; Osterhout, R. E.; Sun, J.; Semi-Synthetic Terephthalic Acid Via Microorganisms That Produce Muconic Acid, US Patent Application US2014302573