Heterogeneous Catalysis of Glucose Mutarotation by Alumina in Dimethyl Sulfoxide. 1. Number and Types of Active Sites from Kinetic Adsorption Data

Article abstract of DOI:10.1021/j150667a046

The kinetics of the heterogeneous catalysis of glucose mutarotation by a standard alumina suspended in dimethyl sulfoxide were determined at 25 deg C.First-order kinetic plots showed a curvature due, first, to relatively slow adsorption of glucose and, second, to progresive deactivation of the catalyst.Partially deactivated catalysts produced linear first-order plots and first-order rate constants could be determined after adsorption equilibrium was attained.Adsorption studies showed the presence of (0.7 +/- 0.02)*10^-4 mol/g of irreversible adsorption sites and two types of reversible adsorption sites; (1.0 +/- 0.1)*10^-4 mol/g of strong adsorption sites with an equilibrium constant for adsorption K₁ = (8.2 +/- 1.2)*10² L/mol, and (1.3 +/- 0.1)*10^-4 mol/g of weak adsorption sites with an equilibrium constant K₂ = 46 +/- 3 L/mol.The variation of the initial rate with concentration showed that only the weak adsorption sites are catalytically active.These have a site density of (5.4*0.6)*10¹³ cm^-2 and a catalytic activity about 9 times that of strong acids in water.The alumina surface offers a more effective environment for mutarotation than water, i. e., the pseudo-first-order rate constant (5*10^-3 s^-1 at 25 deg C) for mutarotation of glucose adsorbed on alumina is greater than that for mutarotation in neutral water.