Studies on mechanism of reaction and density behavior during anhydrous D-fructose mutarotation in the supercooled liquid state.

Recently, we have studied the mutarotation kinetics in D-fructose by means of dielectric spectroscopy. In the present work we investigate density behavior of D-fructose during mutarotation process. By performing volume measurements at temperature T = 303 K and pressure p = 10 MPa we are able to monitor kinetics of this process. As a result we found nearly the same value of the rate constant as previously determined from dielectric measurements. However, these two experimental methods monitor different molecular aspects of mutarotation phenomenon in D-fructose. Dielectric spectroscopy is sensitive to the decay of former ring as well as to the forming of another, while specific volume measurements are sensitive to the forming of new tautomers only. Calculations of activation energy of mutarotation in D-fructose led us to the conclusion, that mechanism of this reaction in amorphous phase could be based on internal proton transfer. Moreover it was found that the main mutarotation path in quenched D-fructose melt is transformation of α,β-furanose to β-pyranose.