Molecular mapping of the acid catalysed dehydration of fructose

Several intermediates and different reaction paths were identified for the acid catalysed conversion of fructose to 5-( hydroxymethyl)-2- furaldehyde (HMF) in different solvents. The structural information combined with results of isotopic-labelling experiments allowed the determination of the irreversibility of the three steps from the fructofuranosyl oxocarbenium ion to HMF as well as the analogous pyranose route.