Effects of γ-Valerolactone/H2O Solvent on the Degradation of pubescens for Its Fullest Utilization.

Solvent-thermal conversion of biomass was promising for obtaining value-added chemicals. However, little was known about the interactions between solvents and biomass in the process, which hindered the effective utilization of biomass. The effects of γ-valerolactone (GVL) and H2O on enhancing pubescens degradation via the cleavage of inter- and intramolecular linkages were studied. At 160 °C, H2O selectively promoted the cleavage of the intermolecular linkages by forming hydrogen bonds, making mainly contributions to hemicellulose dissolution, while GVL and H2O promoted lignin dissolution by forming hydrogen bonds with -OCH3 group of lignin. H2O promoted the cleavage of ß-(1,4)-glycosidic bonds in hemicellulose derived oligomers to xylose, while the oxygen in the ring of GVL might interact with hydroxyl groups of xylose unit to enhance the dehydration of xylose to furfural, whereas GVL with H2O promoted the depolymerization of lignin to oligomers mainly including ß-O-4' and ß-ß' linkages connecting to G and S units.

Mechanism and Origins of Stereoinduction in an Asymmetric Friedel-Crafts Alkylation Reaction of Chalcone Catalyzed by Chiral N, N'-Dioxide-Sc(III) Complex.

The mechanism and selectivity of the asymmetric Friedel-Crafts (F-C) alkylation reaction between indole and chalcone catalyzed by chiral N, N'-dioxide-Sc(III) complexes were investigated at the M06/6-311+G(d,p)//M06/[LANL2DZ,6-31G(d)](SMD,CH2Cl2) level. The reaction occurred via a three-step mechanism: (i) the C3-Cß bond formation by interacting the most mucleophilic C3 center of indole with the most electrophilic Cß center of chalcone; (ii) the abstraction of the proton at the C3 atom of indole by counterion OTf-; (iii) proton transfer from HOTf to the Cα atom of chalcone, generating the F-C alkylation product. The reaction preferred to occur along the favorable re-face attack pathway, producing the dominant R-product. The turnover frequency (TOF) of catalysis was predicted to be 1.59 × 10-7 s-1, with a rate constant of K( T) = 1.58 × 10-7 exp(-29057/ RT) dm6·mol-2·s-1 over the temperature range of 248-368 K. Activation strain model (ASM) and energy decomposition analysis (EDA), as well as noncovalent interaction (NCI) analysis, for the stereocontrolling transition state revealed that the substituent attached to the N atom of the amide subunits as well as the amino acid backbone of ligand played important roles in chiral inductivity. The benzyl group with structural flexibility tended to form strong π-π stacking with substrate as well as the terminal phenyl group of chalcone, stabilizing re-face attack transition state.