Scalable Synthesis of Dimethyl Biphenyl-4,4′-Dicarboxylate from Bio-Derived 4,4′-Dimethylbiphenyl

The homogeneous catalytic oxidation of 4,4′-dimethylbiphenyl (DMBP), an analogue of p-xylene sourced from bioderived 2-methylfuran, to 4,4′-biphenyldicarboxylic acid (BPDA) has been successfully demonstrated in a 50 mL titanium reactor using Mid-Century (MC) process conditions. To adapt to the MC process, the solid DMBP was melted externally at 140 °C and cofed continuously into the reactor with oxygen. Such an operation can produce tens of grams of BPDA with 98.7% purity. In contrast, batch oxidation in which all the solid DMBP is fed initially into the reactor produces BPDA with ∼80% purity due to the substoichiometric O₂/DMBP ratios required for safe operation. Cofeeding of DMBP and O₂ maintains the stoichiometric O₂/DMBP ratio or greater, avoiding O₂ starvation without exceeding safe vapor phase O₂ concentrations. BPDA was easily esterified using methanolic H₂SO₄ to make polymer-grade dimethyl biphenyl 4,4′-dicarboxylate (BPDC, >99%). BPDC has a lower melting point than BPDA and hence is amenable to melt polymerization at milder temperatures. The successful demonstration of DMBP oxidation to produce renewable BPDA via MC process chemistry, widely used in industry to produce terephthalic acid (a BPDA analogue), reduces the economic risk of scaling up DMBP oxidation. As fossil-based feedstock preparation accounts for a majority (∼75%) of the cradle-to-gate global warming potential in the MC process, the use of bioderived feedstock for BPDC manufacture via a similar route has the potential to significantly mitigate the carbon footprint.