(8g) Intensification of Renewable 4,4’-Dimethylbiphenyl Synthesis

Reducing our dependence on petroleum-derived chemicals requires the development of renewable alternatives to replace these established products. Recent investigations demonstrated a pathway to prepare 4,4’-dimethylbiphenyl (DMBP), an attractive platform chemical, from readily available biomass precursors. Harnessing this renewable molecule in consumer plastics through oxidation and esterification to dimethylbiphenyl-4,4’-dicarboxylate (BPDC) and subsequent polymerization into high-performance polyesters demonstrates significant advances in sustainable alternatives.

The synthesis of DMBP follows a two-step process: (1) 2-methylfuran (MF) oxidative coupling to 5,5’-dimethyl-2,2'-bifuran (DMBF), (2) DMBF tandem Diels-Alder-Dehydration with ethylene to afford the desired DMBP. Earlier research identified conditions achieving 63% MF conversion and 59% DMBF yield with a space-time yield of 0.59 mol L^-1h^-1, leaving room for improvements in DMBP production.

A surface response design identified an initial optimum at 44 °C and a MF/solvent molar ratio of 0.71, improving the space-time yield to 0.75 mol L^-1h^-1. Temperature effects at the optimum MF/solvent ratio showed that as the reaction reaches complete conversion of MF, DMBF further reacts to form oligomers. It was found that reducing the time to 1.5 hours at 67 °C led to a MF conversion of 96.2% and a DMBF yield of 77.5% with a DMBF space-time yield of 1.10 mol L^-1h^-1, an 86.4% increase from the baseline. Scale-up efforts resulted in a 44x increase in DMBF production, bringing the process from milligrams to grams.

For the second step, a homogenous Lewis acid catalyst in the Diels-Alder-Dehydration reaction demonstrated a 40x increase in DMBP yield at reduced temperatures compared to the initial protocols. Successful demonstration of the Diels-Alder-Dehydration at a 3 g scale while maintaining selectivity for the DMBP product suggests facile large-scale feasibility. Renewable DMBP was oxidized via the MidCentury process and esterified to BPDC in yields of ~90% and purity of 97%, enabling for polymerization in copolymers.