2,5-Diformylfuran (DFF) and 5-hydroxymethylfurfural (HMF) are interesting platform compounds in the chemical industry. A sustainable one-pot procedure is reported for the transformation of carbohydrates into DFF. Mono-, di- and polysaccharides as well as crude biomass (straw and bran) have been transformed. Depolymerisation, glucose isomerisation to fructose, fructose dehydration and finally oxidation of HMF to DFF are involved. The optimised catalytic system contains boric acid in DMSO for HMF synthesis. Addition of sodium bromide and formic acid to the reaction mixture leads to the formation of DFF. Boric acid is mainly involved in depolymerization, isomerisation and dehydration. Large amounts of boric acid lead to the degradation of HMF. NaBr and water are involved in the selective oxidation of HMF. Formic acid is involved in the dehydration step and it accelerates the oxidation of HMF.