A Zwitterionic Tetrastanna(II) Cyclic Crown

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A Zwitterionic Tetrastanna(II) Cyclic Crown

A zwitterionic tetrastanna(II) cyclic compound comprising of two stannate (II) and two stannyliumylidene in alternating positions of the macrocycle has been synthesized which represents the Sn analogue of 12-crown-4. This has been achieved by the simple deprotonation from a bis(imidazole) using Sn[N(SiMe3)2].


Abstract

A 12-membered zwitterionic tetrastanna(II) cycle 1 having a crown ether-like topology has been isolated from the deprotonation of 1,1′-methylenediimidazole (B) with two equivalents of Sn[N(SiMe3)2]2 (A). The solid-state structure and NMR analysis confirms the tetrastanna(II) cycle 1 to be comprised of two stannate(II) and two stannyliumylidene ion pairs in alternating positions of the heterocycle. Computational analysis shows greater nucleophilicity at the proximally located stannate(II) centers. Nonetheless, the tetrastanna(II) cycle 1 remains poorly reactive due to engagement of SnII lone pair electrons in intramolecular donor-acceptor interactions. Simple deprotonation reaction between Sn[N(SiMe3)2]2 (A) and N-(diisopropylphenyl)imidazole (C) in equimolar ratio has led to a stannylene 2, involving the formation of a Sn−C covalent bond with the anionic imidazol-2-yl carbon center along with the release of NH(SiMe3)2. Compound 2 exists as a dimer, where the unsubstituted ring nitrogen atom coordinated intermolecularly to the other stannylene center.

Estimation of Thermophysical Properties of Pentaalkylguanidinium‐Based Magnetic Ionic Liquids (MILs) with Unusual Thermal Expansion Coefficient

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The thermal expansion coefficient (αexp.), the molecular volume (Vm), the entropy of surface formation (Sa), and the Gibbs energy of surface formation (Ea) of four pentaalkylguanidinium-based MILs [CnTMG][FeCl3Br] (n = 2, 4, 6, 8) were calculated based on the density and surface tension data determined from 278.15 to 323.15 K. In terms of classical semiempirical methods, the standard molar entropy ( S 0 ), the lattice energy (UPOT), the molar enthalpy of evaporation (Δg lH0 m(Tb), Δg lH0 m(298 K)), and the thermal expansion coefficient (αest.) of the MILs were further estimated. The estimation results indicate that the classical semiempirical methods are suitable for estimating the thermophysical properties of the MILs, except the unusual αexp., which were extremely larger than those of representative non-magnetic ionic liquids (ILs). We further optimized the estimation methods and discussed the potential reasons for the unusual thermal expansion coefficient of the MILs.

Modular Synthesis of Multi‐substituted Cyclobutanones Enabled by Oxyallyl Cations

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Comprehensive Summary

Stereoselective synthesis of multi-substituted cyclobutanes with different substituents is still a daunting challenge in organic synthesis. We report here a practical and facile approach to synthesizing all-trans 2,3,4-trisubstituted cyclobutanones from readily available dichlorocyclobutanones. The substitution reaction proceeds smoothly via oxyallyl cation intermediates under mild basic conditions. Further transformation to the synthesis of 1,2,3,4-tetrasubstituted cyclobutanes was also explored.

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PdCu Alloy Catalyst for Inhibition‐free, Low‐temperature CO Oxidation

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Designing robust catalysts for low-temperature oxidation is pertinent to the development of advanced combustion engines to meet increasingly stringent emissions limitations. Oxidation of CO, hydrocarbon and NO pollutants over platinum-group catalysts suffer from strong inhibition due to their competitive adsorption, while coinage metals are generally slow at activating O2. Through computational screening we discovered a PdCu alloy catalyst that completely oxidizes CO below 150 °C without inhibition by NO, propylene or water. This is attributed primarily to geometric effects and the presence of CO bound to Pd sites within the Cu-rich surface of the PdCu alloy. We demonstrate that the novel PdCu catalyst can be used in tandem with a PtPd catalyst to achieve sequential, inhibition-free, complete oxidation of CO in a two-bed system, while also achieving 50% NO conversion below 120 °C. Moreover, neither water nor propylene adversely affect the low temperature CO oxidation activity.

Synthesis of Inexpensive Ternary Metal Oxides by a Co‐Precipitation Method for Catalytic Oxidation of Carbon Monoxide

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Synthesis of Inexpensive Ternary Metal Oxides by a Co-Precipitation Method for Catalytic Oxidation of Carbon Monoxide

The presence of three transition metal oxides in a nanocomposite made it possible to have higher catalytic CO oxidation than that of two. At higher annealing temperatures, the obtained nanocomposite had more crystallinity and thus exhibited lower activity toward the oxidation of CO. The 50 % CO conversion was observed at about 82 °C for the CuO−MnOx−Fe2O3-300 catalyst.


Abstract

By using a simple co-precipitation method, new Fe2O3-based nanocatalysts (samples) were synthesized. The samples were composites of two or three transition metal oxides, MOx (M=Fe, Mn, Co, Ni, and Cu). The average size of CuO crystallites in the composites composed of two oxide components (CuO−Fe2O3) was about 14.3 nm, while in those composed of three (CuO−MnOx−Fe2O3), the composite's phase compositions were almost in the amorphous form when annealing the sample at 300 °C. The latter sample had a specific surface area higher than that of the former, 207.9 and 142.1 g/m2, respectively, explaining its higher catalytic CO oxidation. The CO conversion over the CuO−MnOx−Fe2O3-300 catalyst (1 g of catalyst, 2600 ppm of CO concentration in air, and 1.0 L/min of gas flow rate) begins at about 40 °C; the temperature for 50 % CO conversion (t 50) is near 82 °C; and CO removal is almost complete at t 99 ≈110 °C. The activity of the optimal sample was tested in different catalytic conditions, thereby observing a high durability of 99–100 % CO conversion at 130 °C. The obtained results were derived from XRD, FTIR, BET, SEM, elemental analysis and mapping, as well as catalytic experiments.

Vanadium‐catalyzed Hydration of 2‐Cyanopyrazine to Pyrazinamide with Unique Substrate Specificity

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Vanadium-catalyzed Hydration of 2-Cyanopyrazine to Pyrazinamide with Unique Substrate Specificity

The preparation of pyrazinamide via catalytic hydration of 2-cyanopyrazine is of great economic interest with high atomic economy. Vanadium-nitrogen-carbon materials were fabricated and employed for catalytic hydration of 2-cyanopyrazine with unique substrate specificity. This work expands the application of vanadium-based catalysts for nitrile hydration reactions.


Abstract

Pyrazinamide is an important medicine used for the treatment of tuberculosis(TB). The preparation of pyrazinamide via catalytic hydration of 2-cyanopyrazine is of great economic interest with high atomic economy. Heterogeneous non-precious transition metal-catalyzed hydration of nitriles under neutral reaction conditions would be rather attractive. Herein vanadium-nitrogen-carbon materials were fabricated and employed for selective hydration of nitriles using water as both the solvent and reactant. 2-Cyanopyrazine could be smoothly converted into to pyrazinamide with unique substrate specificity. Additives with different N and O atoms could significantly affect hydration of 2-cyanopyrazine due to competitive adsorption/coordination in the reaction system. This work provides a new approach for non-precious metal catalyzed hydration of nitriles.

Synthesis of Thiophene‐Substituted Ketones via Manganese‐Catalyzed Dehydrogenative Coupling Reaction

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Synthesis of Thiophene-Substituted Ketones via Manganese-Catalyzed Dehydrogenative Coupling Reaction

Herein, we reports an efficient and green one-step method for synthesizing thiophene-substituted ketones from 2-thiophenemethanol and ketones via dehydrogenative coupling using manganese complexes as catalysts. Utilizing this strategy, we carried out an efficient and diverse reaction of ketones with 2-thiophenemethanol, and successfully synthesized a series of thiophene-substituted saturated ketones and α, β-unsaturated ketones in good isolated yields.


Abstract

This study reports an efficient and green one-step method for synthesizing thiophene-substituted ketones from 2-thiophenemethanol and ketones via dehydrogenative coupling using manganese complexes as catalysts. The manganese complex demonstrated a broad applicability under mild conditions and extended the range of usable substrates. Utilizing this strategy, we carried out an efficient and diverse reaction of ketones with 2-thiophenemethanol, and successfully synthesized a series of thiophene-substituted saturated ketones and α, β-unsaturated ketones in good isolated yields.

Visible‐Light‐Driven Furfural Oxidation over CuOx/Nb2O5

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Visible-Light-Driven Furfural Oxidation over CuOx/Nb2O5

Research on the oxidation of furfural to maleic anhydride (MA) suffers from low efficiency, solvent corrosion, and harsh conditions. CuOx/Nb2O5 was prepared as photocatalyst to catalyze furfural oxidation to MA and 5-hydroxy-2(5H)-furanone (HF) selectively, and can absorb visible light due to the ligand to metal charge transfer (LMCT) with adsorbed furfural molecules.


Abstract

Maleic anhydride (MA) is an important polyester monomer that can be produced from oxidizing renewable furfural derived from biomass. However, MA generation from furfural requires harsh reaction conditions, and suffers from low efficiency and solvent corrosion. Herein, we design a Nb2O5 photocatalyst loaded of highly dispersed CuOx (CuOx/Nb2O5), which selectively catalyzes furfural oxidation to MA and the precursor (5-hydroxy-2(5H)-furanone, HF). Due to CuOx loading and forming a complex of ligand to metal charge transfer (LMCT) between the Nb2O5 surface and adsorbed furfural, the CuOx/Nb2O5 absorbs visible light to activate furfural though Nb2O5 has a large band-gap energy (3.2 eV). Singlet oxygen (1O2) is the key active species for C−C bond cleavage and CO generation. MA and HF is produced with a combined yield of 59 % under optimized conditions. This work provides a mild way to provide renewable maleic anhydride via oxidative C−C bond cleavage.

Do Vermicompost Applications Improve Growth Performance, Pharmaceutically Important Alkaloids, Phenolic Content, Free Radical Scavenging Potency and Defense Enzyme Activities in Summer Snowflake (Leucojum aestivum L.)?

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Do Vermicompost Applications Improve Growth Performance, Pharmaceutically Important Alkaloids, Phenolic Content, Free Radical Scavenging Potency and Defense Enzyme Activities in Summer Snowflake (Leucojum aestivum L.)?


Abstract

Leucojum aestivum L. contains galanthamine and lycorine, which are two pharmaceutically valuable alkaloids. Vermicompost (VC), an organic waste product created by earthworms enhances soil quality and can improve the medicinal quality of the plant that is crucial to the pharmaceutical industry. The aim of this study was to determine the effects of four different VC concentrations (5 %, 10 %, 25 %, and 50 %) on L. aestivum growth parameters, alkaloid levels (galanthamine and lycorine), total phenol-flavonoid content, free radical scavenging potential, and defense enzyme activities (SOD and CAT) compared to control (no VC). The width, length, and fresh weight of the leaves were improved by 10 % VC treatment. The highest total phenolic content was found in the bulbs and leaves treated with 50 % VC. HPLC-DAD analysis of alkaloids showed that 10 % and 50 % VC treatments contained the most galanthamine in the bulb and leaf extracts, respectively. The application of 25 % VC was the most efficient in terms of lycorine content in both extracts. CAT activity was elevated at 10 %, 25 %, and 50 % VC. Based on the growth performance and galanthamine content of the bulbs and leaves, it can be concluded that a 10 % VC application was the most effective in the cultivation of L. aestivum.