The concurrent formation of furan-2, 5-and furan-2, 4-dicarboxylic acid under solvent free conditions via a disproportionation reaction is described. By reacting potassium-2-furoate at 260° C in the presence of 22 mol% of (Lewis acidic) catalysts like CdI2 or ZnCl2, potassium- 2-furoate is disproportionated to furan and furandicarboxylic acids. Besides furan and furan- 2, 5-dicarboxylic acid (2, 5-FDCA) as the main products, furan-2, 4-dicarboxylic acid (2, 4- ...