Jennifer Lee and George Kraus of Iowa State University have published a new method of producing dimethyl terephthalate, a precursor to polyethylene terephthalate (PET), from renewable sources. In this new work the reaction between methyl coumalate (the esterified dimer of malic acid) and methyl pyruvate (the ester of pyruvic acid) is optimised to provide dimethyl terephthalate in 95% yield.
This is the latest of several approaches currently being developed to supplant the current manufacturing process that produces PET from finite fossil resources. These include the valorisation of citrus waste and the reaction of ethylene with 2,5-dimethylfuran. As is true for the zeolite catalysed fast pyrolysis of certain bio-based resources, these other green methods produce an intermediate aromatic compound, p-xylene or sometimes p-cymene, which must later be oxidised to terephthalic acid. This oxidation reaction is present in the conventional petroleum derived synthesis of PET. The new uncatalysed, solvent-free method of Lee and Kraus circumvents the oxidation stage, and by doing so shortens the synthetic procedure and avoids the use of cobalt or manganese oxidation catalysts, which from an elemental sustainability perspective are vulnerable to depletion.
Free to access until 4th March:
One-pot formal synthesis of biorenewable terephthalic acid from methyl coumalate and methyl pyruvate, J. J. Lee and G. A. Kraus, Green Chemistry, DOI: 10.1039/C3GC42487A
