Asymmetric alkene epoxidation by Mn(III)salen catalyst in ionic liquids

Room Temperature Ultrafast Oxidative Desulfurization with Sodium Hypochlorite in the Presence of Silica-Supported Catalysts

A series of silica-supported catalysts containing molybdenum, tungsten, and vanadium oxides as the active phase was investigated in the process of oxidative desulfurization with sodium hypochlorite. It was shown for the first time that catalysts containing vanadium oxide as the active phase are more stable under oxidation conditions with sodium hypochlorite and retain their effectiveness at increased dosages of the oxidant and at high initial sulfur contents. The catalysts were characterized in detail by a complex of methods: Fourier transform infrared, X-ray spectral fluorescence, transmission electron microscopy, scanning electron microscopy, and low-temperature nitrogen adsorption/desorption. Key factors affecting the oxidation of dibenzothiophene (DBT) were investigated: oxidant and catalyst amount, oxidation time, initial sulfur content, and acetonitrile amount. Under optimized conditions, the DBT conversion rate was 100% in 5 min at room temperature (25 °C), NaClO/S molar ratio 6:1, catalyst amount 2 wt %. In the real sample of the straight-run diesel fraction, the sulfur content was reduced from 10,100 to 3030 ppm. The V(10%)/SiO2 catalyst retains its activity for 5 oxidation-regeneration cycles.

Establishing Predictive Models for Solvatochromic Parameters of Ionic Liquids

The use of ionic liquids (ILs) in applications ranging from catalysis to reaction media in organic synthesis has been successfully demonstrated in several cases. For any given IL application, fundamental properties, such as viscosity, thermal stability, and toxicity have to be considered. Another property of interest is the polarity, which is a crucial indicator of solvent effects on chemical processes. Given the near-infinite combinations of cations and anions, experimental determination of solvatochromic parameters, such as the hydrogen-bond acidity and basicity, and dipolarity-polarizability is prohibitive. To address this, we evaluate the utility of alternative schemes based on parameters derived from COSMO-RS (COnductor-like Screening MOdel for Real Solvents) computations. The scheme is applied to a large library of yet-to-be-synthesized ionic liquids, to identify promising candidates for applications in biomass dissolution.

Mechanistic Model for Enantioselective Intramolecular Alkene Cyanoamidation via Palladium-Catalyzed C-CN Bond Activation

We studied key aspects of the mechanism of Pd-catalyzed C-CN bond activation and intramolecular enantioselective alkene cyanoamidation. An Abboud-Abraham-Kamlet-Taft (AAKT) linear solvation energy relationship (LSER) model for enantioselectivity was established. We investigated the impact of Lewis acid (BPh3), Lewis base (DMPU), and no additives. BPh3 additive led to diminished enantioselectivity and differing results in 13CN crossover experiments, initial rate kinetics, and natural abundance 12C/13C kinetic isotope effect measurements. We propose two catalytic mechanisms to account for our experimental results. We propose that the DMPU/nonadditive pathway passes through a κ2-phosphoramidite-stabilized Pd+ intermediate, resulting in high enantioselectivity. BPh3 prevents the dissociation of CN-, leading to a less rigid κ2-phosphoramidite-neutral Pd intermediate.

Reusable manganese compounds containing pyrazole-based ligands for olefin epoxidation reactions

New robust and effective Mn-pyrazolyl catalysts for olefin epoxidation in [bmim]PF₆ : CH₃CN, with good activity even after several reuses, are described. The cis → trans isomerization in the epoxidation of cis-β-methylstyrene is confirmed through computational calculations.

Structure and asymmetric epoxidation reactivity of chiral Mn(iii) salen catalysts modified by different axial anions

The axial anions influence the electronic structure, steric configuration, and enantioselectivity of the chiral Mn(iii) salen complexes.