Copper(I) iodide catalyzed redistribution of aromatic carboxylic acids

Copper(I) iodide catalyzes the disproportionation of aromatic and heteroaromatic carboxylic acids to give dicarboxylic acids. Potassium furoate heated to 280 – 300 °C in the presence of 10 mol % CuI under carbon dioxide (40 bar) forms dipotassium 2,5-furandicarboxylate (2,5-FDCK), which is isolated as pure 2,5-dicarboxylic acid (2,5-FDCA) in up to 75 % isolated yield and in excellent selectivity over the regioisomeric 2,4-furandicarboxylate (92 % selectivity). Starting materials are recovered in experiments lacking CuI or with pressurized N2 replacing CO2, whereas high conversion and low yields of 2,5-FDCA are obtained with moderate CO2 pressures, suggesting several roles for carbon dioxide in the transformation. Similarly, potassium benzoate heated to 320 – 350 °C in the presence of 10 mol % CuI under carbon dioxide (40 bar) produces terephthalic acid after workup in up to 60 % yield.