MP2, CCSD(T), and Density Functional Theory Study of the 2‑Butyl Cation: New Insight into the Methyl- and Hydrogen-Bridged Structures

Using the MP2, CCSD­(T), and DFT (B3LYP) methods, the structures and energies of the 2-butyl cation (C₄H₉⁺) were calculated. Energetically, the C–C hyperconjugated structure <b>1</b> and hydrogen-bridged structure <b>2</b> were found to be almost identical at all levels. The ¹³C NMR chemical shifts of <b>1</b> and <b>2</b> were computed by the GIAO-CCSD­(T) method using different geometries. On the basis of calculated relative energies and calculated ¹³C NMR chemical shifts, an equilibrium involving <b>1</b> and <b>2</b> (in a 50:50 ratio) seemed likely responsible for the experimentally observed ¹³C NMR chemical shifts in superacid solutions at −80 °C. However, on the basis of computed and experimental frequencies the hydrogen-bridged structure <b>2</b> is most likely responsible for the experimentally observed frequencies in the solid state at −125 °C

Comparative Study of Alkane Dications (Protonated Alkyl Cations, C_<i>n</i>H_2<i>n</i>+2²⁺) and Their Isoelectronic Boron Cation Analogues

Comparative study of the superelectrophilic alkane dications (C_<i>n</i>H_2<i>n</i>+2²⁺, <i>n</i> = 1–5) and their isoelectronic boron cation analogues was carried out using the ab initio method at the MP2/cc-pVTZ level. The structure, bonding, and relative stability of doubly charged alkane dications and monocharged boron cation analogues are discussed. These studies contribute to our general understanding of the superelectrophilic activation of alkyl cations as well as the electrophilic reactivity of C–H and C–C single bonds

One-Pot Conversion of Methane to Light Olefins or Higher Hydrocarbons through H‑SAPO-34-Catalyzed in Situ Halogenation

Methane was converted to light olefins (ethene and propene) or higher hydrocarbons in a continuous flow reactor below 375 °C over H-SAPO-34 catalyst via an in situ halogenation (chlorination/bromination) protocol. The reaction conditions can be efficiently tuned toward selective monohalogenation of methane to methyl halides or their in situ oligomerization to higher hydrocarbons. The presence of C5+ hydrocarbons in the reaction products clearly indicates that by using a properly engineered catalyst under optimized reaction conditions, hydrocarbons in the gasoline range can be produced. This approach has significant potential for feasible application in natural gas refining to gasoline and materials under moderate operational conditions

Integrative CO₂ Capture and Hydrogenation to Methanol with Reusable Catalyst and Amine: Toward a Carbon Neutral Methanol Economy

Herein we report an efficient and recyclable system for tandem CO₂ capture and hydrogenation to methanol. After capture in an aqueous amine solution, CO₂ is hydrogenated in high yield to CH₃OH (>90%) in a biphasic 2-MTHF/water system, which also allows for easy separation and recycling of the amine and catalyst for multiple reaction cycles. Between cycles, the produced methanol can be conveniently removed in vacuo. Employing this strategy, catalyst Ru-MACHO-BH and polyamine PEHA were recycled three times with 87% of the methanol producibility of the first cycle retained, along with 95% of catalyst activity after four cycles. CO₂ from dilute sources such as air can also be converted to CH₃OH using this route. We postulate that the CO₂ capture and hydrogenation to methanol system presented here could be an important step toward the implementation of the carbon neutral methanol economy concept

Manganese-Catalyzed Sequential Hydrogenation of CO₂ to Methanol via Formamide

Mn­(I)-PNP pincer catalyzed sequential one-pot homogeneous CO₂ hydrogenation to CH₃OH by molecular H₂ is demonstrated. The hydrogenation consists of two partsN-formylation of an amine utilizing CO₂ and H₂, and subsequent formamide reduction to CH₃OH, regenerating the amine in the process. A reported air-stable and well-defined Mn-PNP pincer complex was found active for the catalysis of both steps. CH₃OH yields up to 84% and 71% (w.r.t amine) were obtained, when benzylamine and morpholine were used as amines, respectively; and a TON of up to 36 was observed. In our opinion, this study represents an important development in the nascent field of base-metal-catalyzed homogeneous CO₂ hydrogenation to CH₃OH

Bi-reforming of Methane from Any Source with Steam and Carbon Dioxide Exclusively to Metgas (CO–2H₂) for Methanol and Hydrocarbon Synthesis

A catalyst based on nickel oxide on magnesium oxide (NiO/MgO) thermally activated under hydrogen is effective for the bi-reforming with steam and CO₂ (combined steam and dry reforming) of methane as well as natural gas in a tubular flow reactor at elevated pressures (5–30 atm) and temperatures (800–950 °C). By adjusting the CO₂-to-steam ratio in the gas feed, the H₂/CO ratio in the produced syn-gas could be easily adjusted in a single step to the desired value of 2 for methanol and hydrocarbon synthesis

Self-Assembled Monolayers of <i>n</i>‑Alkanethiols Suppress Hydrogen Evolution and Increase the Efficiency of Rechargeable Iron Battery Electrodes

Iron-based rechargeable batteries, because of their low cost, eco-friendliness, and durability, are extremely attractive for large-scale energy storage. A principal challenge in the deployment of these batteries is their relatively low electrical efficiency. The low efficiency is due to parasitic hydrogen evolution that occurs on the iron electrode during charging and idle stand. In this study, we demonstrate for the first time that linear alkanethiols are very effective in suppressing hydrogen evolution on alkaline iron battery electrodes. The alkanethiols form self-assembled monolayers on the iron electrodes. The degree of suppression of hydrogen evolution by the alkanethiols was found to be greater than 90%, and the effectiveness of the alkanethiol increased with the chain length. Through steady-state potentiostatic polarization studies and impedance measurements on high-purity iron disk electrodes, we show that the self-assembly of alkanethiols suppressed the parasitic reaction by reducing the interfacial area available for the electrochemical reaction. We have modeled the effect of chain length of the alkanethiol on the surface coverage, charge-transfer resistance, and double-layer capacitance of the interface using a simple model that also yields a value for the interchain interaction energy. We have verified the improvement in charging efficiency resulting from the use of the alkanethiols in practical rechargeable iron battery electrodes. The results of battery tests indicate that alkanethiols yield among the highest faradaic efficiencies reported for the rechargeable iron electrodes, enabling the prospect of a large-scale energy storage solution based on low-cost iron-based rechargeable batteries

Anhydrous Proton-Conducting Membrane Based on Poly-2-Vinylpyridinium Dihydrogenphosphate for Electrochemical Applications

Anhydrous electrolytes with high proton conductivity and adequate chemical stability in the temperature range of 120–180 °C can be very useful in electrochemical devices such as fuel cells, sensors, and electrolyzers. Developing such proton-conducting materials has been challenging. We have fabricated and characterized the performance of such membranes, based on poly-2-vinylpyridinium dihydrogenphosphate (P2VP-DHP), that can operate in the range of 105–180 °C under anhydrous conditions. The ionic conductivity of the membrane was 0.01 S cm^–1 at 140 °C. Proton conduction occurs by ionization of the quaternary ammonium group and by Grotthus-type transport that involves the rapid rotation of the dihydrogenphosphate anion. The activation energy for proton transport was 50 kJ/mol. The transport number of the proton was measured by impedance spectroscopy and potential-step techniques. The measured value was in the range of 0.17–0.20. A membrane-and-electrode assembly using the P2VP-DHP was tested as an electrochemical hydrogen pump. This demonstration shows the advantage of membranes based on a polymer amine salt in electrochemical applications that require operating under water-free conditions. Weight loss measurements at 120 °C in air confirmed the thermal and oxidative stability of the membrane. The properties of the P2VP-DHP membrane reported here provide the basis for further development of proton-conducting polymer electrolyte membranes for operating temperatures above 100 °C in anhydrous environments

Nucleophilic Trifluoromethylation of Carbonyl Compounds: Trifluoroacetaldehyde Hydrate as a Trifluoromethyl Source

A feasible nucleophilic trifluoromethylating protocol has been developed using trifluoroacetaldehyde hydrate as an atom-economical trifluoromethyl source. The reaction was found to be applicable to the nucleophilic trifluoromethylation of a broad spectrum of carbonyl compounds with satisfactory yields in general. DFT calculations have been performed to provide mechanistic insight into the present and related reactions employing 2,2,2-trifluoro-1-methoxyethanol and hexafluoroacetone hydrate

Direct Difluorination–Hydroxylation, Trifluorination, and C(sp²)–H Fluorination of Enamides

A direct double functionalization involving both difluorination and hydroxylation of enamides is reported. With the appropriate combination of an electrophilic fluorinating reagent and H₂O, the most convenient and ecofriendly hydroxylating agent, the preparation of 3-(difluoroalkyl)-3-hydroxyisoindolin-1-ones was achieved under basic or Brønsted acidic conditions. Suitable conditions for trifluorination as well as C­(sp²)–H fluorination were also identified. Subsequent asymmetric functionalization of the obtained <i>gem</i>-difluorinated products has also been demonstrated