Zeolites as Solid Solvents: Explaining the Chloromethane Hydrolysis over Metal-Exchanged Zeolite Y by DFT Calculations.

We report a theoretical DFT study of the reaction pathways for chloromethane hydrolysis over metal-exchanged zeolites (Li, Na, K, and Mg). A cluster of 78 T atoms (T referring to Si or Al atoms), comprising the zeolite Y super cavity coupled with the sodalite cage and three hexagonal prism units (SiAl OH; = 1 or 2), was used in the calculations. The study was carried out using the ONIOM method.

General Approach to Silica-Supported Salens and Salophens and Their Use as Catalysts for the Synthesis of Cyclic Carbonates from Epoxides and Carbon Dioxide.

General routes for the synthesis of silica-immobilized symmetrical and unsymmetrical salophen and salen ligands and metal complexes have been developed starting from the natural product 4-allylanisole (methyl-chavicol and estragole). The key step of the syntheses is a microwave-assisted, platinum oxide catalyzed hydrosilylation of the terminal alkene of 5-allyl-2-hydroxybenzaldehyde to afford a sol-gel precursor which can be immobilized into silica before or after conversion to salen and salophen ligands to afford unsymmetrical and symmetrical silica-supported ligands, respectively. Both the symmetrical and unsymmetrical silica-supported salophens were found to catalyze the formation of cyclic carbonates from epoxides and carbon dioxide with catalytic activities at least comparable to those previously reported for non-immobilized homogeneous salophens.

Synthesis, Characterization, and CO Uptake of Adsorbents Prepared by Hydrothermal Carbonization of Chitosan.

Chitosan, a heteropolysaccharide obtained from the N-deacetylation of chitin, has stood out as a raw material to produce CO adsorbents. In this work, we report the hydrothermal carbonization (HTC) of chitosan for different times and the potential of the materials for CO adsorption. Elemental analysis indicated that the carbon weight content increases, whereas the relative amount of oxygen atoms decreases upon increasing the time of HTC.

Direct Carbonation of Glycerol with CO Catalyzed by Metal Oxides.

Five metal oxides (ZnO, SnO , Fe O , CeO , La O ) were produced by the sol-gel method and tested in the direct carbonation of glycerol with CO . Initial tests with Fe O showed that the best reaction condition was 180 °C, 150 bar, and 12 h. The other oxides were evaluated at these conditions and were all active to the formation of glycerol carbonate.

Green acetylation of solketal and glycerol formal by heterogeneous acid catalysts to form a biodiesel fuel additive.

A glut of glycerol has formed from the increased production of biodiesel, with the potential to integrate the supply chain by using glycerol additives to improve biodiesel properties. Acetylated acetals show interesting cold flow and viscosity effects. Herein, a solventless heterogeneously catalyzed process for the acetylation of both solketal and glycerol formal to new products is demonstrated.

Dynamic behaviour of carbocations on zeolites: mobility and rearrangement of the C4H7(+) system.

The mobility and rearrangement of the C4H7(+) system over Chabazite were studied using ab initio molecular dynamics. The results indicated the high mobility of the cations, which can rearrange within picosecond time intervals. Experimental studies of nucleophilic substitution supported the theoretical findings.

Glycerol acetals as anti-freezing additives for biodiesel.

Glycerol acetals from butanal, pentanal, hexanal, octanal and decanal were prepared with the use of Amberlyst-15 acid resin as catalyst. The glycerol conversion decreases with the size of the hydrocarbon chain. This fact has been associated with formation of micelles and aggregates of the aldehyde to minimize the interaction between the polar glycerol molecule with the hydrocarbon chain.

Topological insights into the nature of the halogen-carbon bonds in dimethylhalonium ylides and their cations.

In this study the nature of the bonding in a series of dimethylhalonium ylides (fluoronium, chloronium, bromonium and iodonium) was analyzed by means of topological methodologies (AIM and ELF analysis), to document the changes in the nature of the C-X bonds (X = F, Cl, Br, I) upon the series. For the sake of comparison the same study was performed on the corresponding dimethylhalonium cations (XC 2H 6 (+)) and the XCH 3 series. The wave functions used for the topological analysis were obtained at B3LYP level using extended triple-zeta basis sets.

Rearrangement, nucleophilic substitution, and halogen switch reactions of alkyl halides over NaY Zeolite: formation of the bicyclobutonium cation inside the zeolite cavity.

Rearrangement and nucleophilic substitution of cyclopropylcarbinyl bromide over NaY and NaY impregnated with NaCl was observed at room temperature. The first-order kinetics are consistent with ionization to the bicyclobutonium cation, followed by internal return of the bromide anion or nucleophilic attack by impregnated NaCl to form cyclopropylcarbinyl, cyclobutyl, and allylcarbinyl chlorides. The product distribution analysis revealed that neither a purely kinetic distribution, similar to what is found in solution, nor the thermodynamic ratio, which favors the allylcarbinyl halide, was observed.

Intrinsic acidity of dimethylhalonium ions: evidence for hyperconjugation in dimethylhalonium ylides in the gas phase.

The intrinsic acidity of dimethylhalonium ions has been determined, both by theoretical methods and by gas-phase reactions of the isolated ions with pyridine bases. The calculated geometry of the dimethylhalonium ions shows a bent structure with the C-X-C angle decreasing in the order Cl > Br > I. Thermochemical calculations for the reaction of the dimethylhalonium ions with pyridine, 2,6-dimethylpyridine, and 2,6-di-tert-butylpyridine indicate that proton transfer, with the formation of the dimethylhalonium ylide is endothermic, whereas methyl transfer, with formation of methylhalide, is exothermic.

A fast and easy computational method to calculate the (13)C NMR chemical shift of organic species adsorbed on the zeolite surface.

Calculations of the 13C NMR chemical shifts for the methoxy and ethoxy groups adsorbed on Y and ZSM-5 zeolites were computed at GIAO/B3LYP/6-31+G*//MM+ level of theory, using a cluster representing a real part of the zeolites. The Y zeolite was represented by a cluster with 168 atoms, while ZSM-5 was represented by a cluster with 144 atoms. The calculated chemical shifts agreed well with reported experimental values, showing that the difference in chemical shifts is associated with differences in the geometry of the alkoxides on the two zeolites.

The nature of superacid electrophilic species in HF/SbF(5): a density functional theory study.

A density functional theory study at the B3LYP/6-31++G** + RECP(Sb) level of the HF/SbF(5) superacid system was carried out. The geometries of possible electrophilic species, such as H(2)F(+).Sb(2)F(11)(-) and H(3)F(2)(+).