Furan derivatives, such as 5-hydroxymethylfurfural (HMF) and furfural, obtained from renewable biomass-derived carbohydrates have potential to be sustainable substitutes for petroleum-based building blocks used in production of fine chemicals and plastics. We have studied the production of HMF and furfural by dehydration of fructose, glucose and xylose using a biphasic reactor system, comprised of reactive aqueous phase modified with DMSO, combined with an organic extracting phase consisting of a 7 : 3 (w/w) MIBK–2-butanol mixture or dichloromethane (DCM). Experiments with the MIBK–2-butanol mixture were conducted at a temperature of 443 K using mineral acid catalysts (HCl, H₂SO₄ and H₃PO₄) at a pH from 1.0 to 2.0, whereas experiments with DCM as the extracting solvent were conducted at 413 K and did not require the use of an acid catalyst. The modifiable nature of the biphasic system allowed us to identify preferred DMSO and pH levels for each sugar to maximize the HMF selectivity at high sugar conversions, leading to selectivities of 89%, 91%, and 53% for dehydration of fructose, xylose, and glucose, respectively. Using these reaction conditions for each monosaccharide unit, we can process the corresponding polysaccharides, such as sucrose (a disaccharide of glucose and fructose), inulin (a polyfructan), starch (a polyglucan), cellobiose (a glucose dimer) and xylan (a xylose polysaccharide), with equally good selectivities at high conversions. In addition, we show that the biphasic reactor system can process high feed concentrations (10 to 30 wt%) along with excellent recycling ability. By processing these highly functionalized polysaccharides, that are inexpensive and abundantly available, we eliminate the need to obtain simple carbohydrate molecules by acid hydrolysis as a separate processing step.