Abstract: Processes for the oxidation of carbohydrate dehydration products, such as furanics that can be oxidized to the bio-based monomer 2,5-furandicarboxylic acid (FDCA), are disclosed, according to which certain co-feeds, having been discovered to impart a beneficial reaction stabilizing effect, are oxidized together with the carbohydrate dehydration products. This can advantageously counteract, in whole or in part, detrimental effects of humin impurities present in oxidation feed, with such impurities having been generated as byproducts of the upstream dehydrating step. An important co-feed is para-xylene that can be co-oxidized to form the petroleum-based monomer terephthalic acid (TPA), such that co-processing can beneficially yield two valuable monomers, while improving performance, particularly in terms of reaction stability, over comparable processes in which only the first monomer is produced.