(680b) Intensification of Renewable 4,4'-Dimethylbiphenyl Synthesis Via Oxidative Coupling and Tandem Diels-Alder and Dehydration of 2-Methylfuran

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) from available biomass precursors, an attractive platform chemical for producing metal-organic frameworks, plasticizers, and polymers.

The synthesis of renewable DMBP follows a two-step process: 2-methylfuran (MF) is oxidatively coupled to yield 5,5’-dimethylbifuran (DMBF). DMBF then undergoes tandem Diels-Alder and dehydration with ethylene to afford the desired DMBP. Prior research identified conditions that achieved 63% MF conversion and 59% DMBF yield, leaving room for improvements in DMBP production. We researched process and catalyst alternatives to improve the productivity of this valuable molecule.

A baseline DMBF space-time yield of 0.59 mol L^-1h^-1 was established via the reaction conditions initially reported. A surface response design identified an initial optimum at 44 °C and a MF/solvent molar ratio of 0.713, achieving a DMBF space-time yield of 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 reacts to form undesired byproducts. For maximum productivity, the reaction time was reduced to 1.5 hours at a temperature of 67 °C affording a MF conversion of 96.2% and 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.

For the second step, the use of homogenous Lewis acid catalysts in the Diels-Alder-Dehydration reaction demonstrated a 39.2% increase in DMBP yield compared to the initial protocols. We will report on our continuing efforts to develop an effective and scalable pathway to renewable DMBP, to identify the reaction mechanisms of the desired and undesired side reactions as well as the scale up of the process.