(281g) P-Toluic Acid from Biomass-Derived Coumalic Acid: A Reaction Network Analysis

The Diels-Alder/decarboxylation/dehydrogenation sequential reaction of biomass-derived coumalic acid (CMA) with propylene provides a renewable one-pot reaction pathway to p- toluic acid (pTA), an intermediate that can be used to produce terephthalic acid. A detailed reaction network of the formation of toluic acid (TA) was established by varying the key parameters including temperature, solvent, and reaction time, showing that high yields of TA (85 %) are possible at complete conversion of CMA and that the para to meta selectivity of TA can be controlled by adjusting reaction temperature and time. Changing the reaction media from non-polar (toluene) to polar aprotic (γ-valerolactone) revealed a strong solvent effect with an increase in the formation of TA from 58 % to > 85 %. Performing the reaction of CMA and propylene with and without the presence of catalyst gave additional information about byproduct formation demonstrating the importance of the catalyst presence to quickly dehydrogenate TA intermediates and to prevent unwanted byproduct formation. Product yield and selectivity can be further optimized when water free reaction conditions are applied as accelerated decomposition rates of CMA were observed by adding small amounts of water (5 vol-%) to the solvent.