Kinetic Analysis of Formation and Degradation of 1-Morpholino-1-deoxy-d-fructose

The kinetics of the reaction of glucose with morpholine to produce morpholino-1-deoxy-d-fructose (Amadori product) were studied under experimental conditions that minimize side reactions and maximize Amadori product formation (pH 3.0, T = 100 °C, 90% methanol−water, 6 h). Glucose (0.1 M) was reacted in sealed vials with a series of morpholine solutions (0.1−0.3 M), and similarly morpholine (0.1 M) was reacted with different concentrations of glucose (0.05−0.2 M). At specific time intervals, the samples were analyzed for the presence of reactants and Amadori product by a multidetector HPLC system (diode array and pulsed amperometric detector). Under the experimental conditions, morpholine alone (in the presence of glucose equivalent of sorbitol) and glucose alone (in the presence of morpholine equivalent of triethylamine) did not degrade. Similarly, the degradation of Amadori product (0.02 M) was also studied in the presence of excess glucose. The data obtained were used to study the kinetics of color and fluorescence formation and to calculate the rate constants for the formation and degradation of Amadori product using two approaches:  one involving the use of integrated rate laws and graphical methods and the second involving simultaneous numerical solutions of the differential rate equations followed by optimization, such that the proposed model fits best the data. Both approaches gave comparable results. The second-order rate constant for the formation of morpholine Amadori compound was calculated to be 1.87 M^-1 h^-1. Keywords: Kinetics; morpholine/glucose; color and fluorescence; graphical and numerical analysis