The present invention relates to a method for synthesizing an optionally substituted furoic acid by dehydrating a biomass and oxidizing the optionally substituted furan derived from the dehydration reaction. Water extraction has been incorporated as a step between the dehydration and the oxidation in order to purify the intermediate optionally substituted furan before having it oxidized. Prior to this water extraction, the organic solvent used for dehydration may be separated by evaporation. The provision of the water extraction allows impurities to be separated from the intermediate optionally substituted furan.