A Kinetic Study of Glucose Degradation in Acid Solution*

The degradation of glucose in acid solution was carried out at various temperatures. The first-order rate constants for the decomposition reaction, obtained from the initial rate of formation of 5-hydroxymethylfurfural (5HMF), were consistently higher than those calculated from glucose depletion measurements over long periods of time at temperatures above 100°. At 100° the rate of formation of 5-HMF increased with time for the early portion of the break-down. The rate constant did not coincide with the Arrhenius plot for higher temperatures. This indicates the possibility of a change of mechanism at lower temperatures. The rate data was fitted to kinetic expressions for first-order consecutive reactions. Agreement between calculated and experimental values indicates that the reaction proceeds by the step-wise mechanism. Data obtained from degradation in varying acid concentrations show that the rate constant does not vary linearly with normality. Decomposition in dioxane-water mixtures indicates that the logarithm of the rate constant varies linearly with the reciprocal of the dielectric constant.