Selective conversion of glucose into lactic acid with immobilized ytterbium triflate

Synthesis of Dihydroquinoxalinones from Biomass-Derived Keto Acids and o-Phenylenediamines

A novel catalyst-free cascade amination/cyclization/reduction reaction was developed for the synthesis of various Dihydroquinoxalinones under mild conditions from accessible biomass-derived keto acids and 1,2-phenylenediamines with ammonia borane as a hydrogen donor. This single-step approach enables a simple and eco-friendly route toward the direct synthesis of 12 kinds of Dihydroquinoxalinones in moderate to excellent yields in the green solvent dimethyl carbonate. The results of deuterium-labeling experiments and density function calculations demonstrate that the reductive process proceeds along a double hydrogen transfer pathway. An acceptable yield of Dihydroquinoxalinone can be afforded in a gram-scale experiment, illustrating the practicality of the as-reported reaction system.

The production of lactic acid from chemi-thermomechanical pulps using a chemo-catalytic approach

Previous work has shown that sulfonation and oxidation of chemi-thermomechanical pulps (CTMPs) significantly enhanced enzyme accessibility to cellulose while recovering the majority of carbohydrates in the water-insoluble component. In the work reported here, modified (sulfonated and oxidized) CTMPs derived from hard-and-softwoods were used to produce a DL-mix of lactic acid via a chemo-catalytic approach using lanthanide triflate (Ln (OTf)₃) catalysts (Ln = La, Nd, Er, and Yb). It was apparent that sulfonation and oxidation of chemi-thermomechanical pulps (CTMPs) also enhanced Ln(OTf)₃ catalyst accessibility to the carbohydrate components of the pulps, with the Er(OTf)₃ catalysts resulting in significant lactic acid production. Under optimum conditions (250 °C, 60 min, 0.5 mmol catalyst g^-1 biomass), 72% and 67% of the respective total carbohydrate present in the hard-and-softwood CTMPs could be converted to lactic acid compared to the respective 59% and 51% yields obtained after energy-intensive ball milling.

Functionalized Silicas for Metal-Free and Metal-Based Catalytic Applications: A Review in Perspective of Green Chemistry

Heterogeneous catalysis plays a key role in promoting green chemistry through many routes. The functionalizable reactive silanols highlight silica as a beguiling support for the preparation of heterogeneous catalysts. Metal active sites anchored on functionalized silica (FS) usually demonstrate the better dispersion and stability due to their firm chemical interaction with FSs. Having certain functional groups in structure, FSs can act as the useful catalysts for few organic reactions even without the need of metal active sites which are termed as the covetous reusable organocatalysts. Magnetic FSs have laid the platform where the effortless recovery of catalysts is realized just using an external magnet, resulting in the simplified reaction procedure. Using FSs of multiple functional groups, we can envisage the shortened reaction pathway and, reduced chemical uses and chemical wastes. Unstable bio-molecules like enzymes have been stabilized when they get chemically anchored on FSs. The resultant solid bio-catalysts exhibited very good reusability in many catalytic reactions. Getting provoked from the green chemistry aspects and benefits of FS-based catalysts, we confer the recent literature and progress focusing on the significance of FSs in heterogeneous catalysis. This review covers the preparative methods, types and catalytic applications of FSs. A special emphasis is given to the metal-free FS catalysts, multiple FS-based catalysts and magnetic FSs. Through this review, we presume that the contribution of FSs to green chemistry can be well understood. The future perspective of FSs and the improvements still required for implementing FS-based catalysts in practical applications have been narrated at the end of this review.