5-(Hydroxymethyl)furfural (HMF) and levulinic acid production from glucose in a cascade of reactions using a Lewis acid (CrCl3) catalyst together with a Brønsted acid (HCl) catalyst in aqueous media is investigated. It is shown that CrCl3 is an active Lewis acid catalyst in glucose isomerization to fructose, and the combined Lewis and Brønsted acid catalysts perform the isomerization and dehydration/rehydration reactions. A CrCl3 speciation model in conjunction with kinetics results indicates that the hydrolyzed Cr(III) complex [Cr(H2O)5OH](2+) is the most active Cr species in glucose isomerization and probably acts as a Lewis acid-Brønsted base bifunctional site. Extended X-ray absorption fine structure spectroscopy and Car-Parrinello molecular dynamics simulations indicate a strong interaction between the Cr cation and the glucose molecule whereby some water molecules are displaced from the first coordination sphere of Cr by the glucose to enable ring-opening and isomerization of glucose. Additionally, complex interactions between the two catalysts are revealed: Brønsted acidity retards aldose-to-ketose isomerization by decreasing the equilibrium concentration of [Cr(H2O)5OH](2+). In contrast, Lewis acidity increases the overall rate of consumption of fructose and HMF compared to Brønsted acid catalysis by promoting side reactions. Even in the absence of HCl, hydrolysis of Cr(III) decreases the solution pH, and this intrinsic Brønsted acidity drives the dehydration and rehydration reactions. Yields of 46% levulinic acid in a single phase and 59% HMF in a biphasic system have been achieved at moderate temperatures by combining CrCl3 and HCl.

No abstract

No abstract

A comprehensive model for calculating the electrical conductivity of multicomponent aqueous systems has been developed. In the infinite-dilution limit, the temperature dependence of ionic conductivities is calculated on the basis of the concept of structure-breaking and structuremaking ions. At finite concentrations, the concentration dependence of conductivity is calculated from the dielectric continuum-based mean-spherical-approximation (MSA) theory for the unrestricted primitive model. The MSA theory has been extended to concentrated solutions by using effective ionic radii. A mixing rule has been developed to predict the conductivity of multicomponent systems from those of constituent binary cation-anion subsystems. The effects of complexation are taken into account through a comprehensive speciation model coupled with a technique for predicting the limiting conductivities of complex species from those of simple ions. The model reproduces the conductivity of aqueous systems ranging from dilute to concentrated solutions (up to 30 mol/kg) at temperatures up to 573 K with an accuracy that is sufficient for modeling industrially important systems. In particular, the conductivity of multicomponent systems can be accurately predicted using data for single-solute systems.