Lewis Acid Research Articles

Purine nucleosides as selective inhibitors of butyrylcholinesterase - a multidisciplinary study.

The computational study of the most relevant interactions of the nanomolar purine nucleoside BuChE selective inhibitor has shown that the benzyl group at position 2 and the purine acetamido group are required for activity. In addition, the synthesis of a 6-iodinated radiolabelled analogue and the study of in vivo bioavailability have shown a low percentage of uptake by the brain after 1 hour. These results encouraged the synthesis of a small library of new compounds, focussing on deoxygenation at other positions aiming to access active and more bioavailable structures. Deoxygenation at positions 4 and 3,4 afforded new nucleosides that displayed low inhibition of both cholinesterases, while deoxygenation at position 6 and the lyxopyranosyl group afforded the two most active compounds (IC50 ranging from 3.7 to 7.8 μM); one of them was not cytotoxic at the bioactive concentration, while the other one showed a slight cytotoxicity. Interestingly, these structures exhibited the same anomeric stereochemistry and were purine N7-linked, similar to the lead compound 3 (IC50 = 50 nM), thus confirming the importance of the αDN7 purine nucleoside structure. Thus, optimization of the purine nucleoside synthetic procedure was carried out by changing the reaction temperature, the anomeric leaving group or the Lewis acid. The most satisfactory reaction yields and regioselectivity were obtained by using the original N-glycosylation conditions at 25 °C, which afforded the highest yield of 25% when compared to the 8% of the αDN7 purine nucleoside, and an increase in N7 regioselectivity, with the total N7 nucleoside yield increasing from 36% to 52%.

An Untethered and Formal Intermolecular Hexadehydro-Diels-Alder Reaction: Alkynylboronates with 2-(1,3-Butadiynyl)pyridines.

We show that 2-diynylpyridine and a Bpin-terminated monoyne or diyne will cross-react to form benzyne intermediates. These reactive intermediates are captured by various in situ trapping agents to give products of three-component reactions. Various control reactions, substrate modification, binding studies, and DFT analysis suggest that a small amount of a noncovalent Lewis acid-base complex is the active species within which the diyne and diynophile engage to produce the benzyne. Only a single isomeric benzyne is formed when a Bpin-diyne is used; this selectivity is rationalized by the geometric distortion seen in the DFT-computed diradical intermediate.

Correlation between Noncovalent Bond Strength and Spectroscopic Perturbations within the Lewis Base.

Me2CO was allowed to interact with 20 different Lewis acids so as to engage in various sorts of noncovalent interactions, encompassing hydrogen, halogen, chalcogen, pnictogen, and tetrel bonds. Density functional theory computations evaluated the interaction energy of each dyad, which was compared with spectroscopic, geometric, AIM, and energy decomposition elements so as to elucidate any correlations. The red shift of the C═O stretching frequency, and the changes in the nuclear magnetic resonance shielding of the O and C atoms of acetone, are closely correlated with the interaction energy so can be used to estimate the latter from experimental measurements. The standard AIM measures at the bond critical point, ρ, ∇2ρ, and V also correlate with the energy, albeit not as well as the spectroscopic parameters. The σ-hole depth on the Lewis acid is not well correlated with the energetics, due in part to the fact that electrostatics in general are not an accurate metric of bond strength.

Multifunctional Magnetic Chiral HKUST MOF Decorated by Triazine, Fe3O4, and Cu(l-Proline)2 Complex for Green and Mild Asymmetric Catalysis.

A multifunctional magnetic chiral metal-organic framework (MOF) was developed for asymmetric applications by utilizing strategies of chiralization and multifunctionalization. Cu(l-proline)2-Triazine/Fe3O4@SiO2-NH2 was employed as a chiral secondary agent to synthesize a chiral hybrid nanocomposite within a MOF. The use of a chiral secondary agent efficiently induces chirality in an achiral MOF structure that cannot be directly chiralized. The HKUST-1@Cu(l-proline)2-Triazine/Fe3O4@SiO2-NH2 nanocomposite was afforded by first anchoring chiral Cu(l-proline)2 on the Triazine/Fe3O4@SiO2-NH2 surface and then encapsulating the Cu(l-proline)2-Triazine/Fe3O4@SiO2-NH2 nanoparticles with HKUST-1 via in situ ultrasonication synthesis. In the synthesis of the HKUST-1@Cu(l-proline)2-Triazine/Fe3O4@SiO2-NH2 nanocomposite, Cu(l-proline)2 was used as a chiral complex due to its Lewis acidic/basic hydroxyl groups, carboxylate carbonyl functional groups acting as Lewis bases, an active Cu site functioning as a Lewis acid center, and azine groups of TCT acting as Lewis bases, all synergistically interacting with the Lewis acidity of the Cu centers in HKUST-1. To assess these synergic effects, HKUST-1@Cu(l-proline)2-Triazine/Fe3O4@SiO2-NH2 was used in the formation of an asymmetric C-C bond in nitroaldol condensation and asymmetric cycloaddition of CO2 to epoxides. The findings demonstrated that under mild and green conditions, in both the asymmetric nitroalcohol condensation and the asymmetric cycloaddition of CO2, HKUST-1@Cu(l-proline)2-Triazine/Fe3O4@SiO2-NH2 had better enantioselectivity than the Cu(l-proline)2-Triazine/Fe3O4@SiO2-NH2 nanoparticles and a higher selectivity toward β-nitroalcohol and cyclic carbonate over the pure HKUST-1. Despite its simple and easy synthesis, HKUST-1@Cu(l-proline)2-Triazine/Fe3O4@SiO2-NH2 exhibited exceptional performance in the asymmetric nitroaldol condensation and asymmetric cycloaddition of CO2 to epoxides. Additionally, the mechanism of the reactions was depicted with reference to the total energy of the reactants, intermediates, and products.

Surface frustrated Lewis pairs in titanium nitride enable gas phase heterogeneous CO2 photocatalysis

Gas-phase heterogeneous catalytic CO2 hydrogenation to commodity chemicals and fuels via surface frustrated Lewis pairs is a growing focus of scientific and technological interest. Traditional gas-phase heterogeneous surface frustrated Lewis pair catalysts primarily involve metal oxide-hydroxides (MOH•••M). An avenue to improve the process performance metrics lies in replacing the Lewis base MOH with a stronger alternative; an intriguing example being the amine MNH2 in metal nitrides. This study establishes a proof-of-concept that an amine-type photoactive surface frustrated Lewis pair (MNH2•••M) can be constructed in titanium nitride (TiNxOy) when integrated with a nanoscale platinum spillover co-catalyst. This surface frustrated Lewis pair, comprising Ti-NH2 as the Lewis base and low-valent Ti as the Lewis acid, facilitates the gas-phase light-assisted heterogeneous reverse water-gas shift reaction. The reaction proceeds via a surface-active carbamate intermediate, Ti-(H2N-COO)-Ti, whereby the synergism of Lewis acidic and Lewis basic sites endows it with superior performance indicators compared to TiNxOy alone, as well as conventional platinum supported metal oxides.

Synthesis and Characterisation of Phosphino-Aryloxide Rare Earth Complexes.

A series of homoleptic rare earth (RE) complexes bearing phosphino-aryloxide ligands (1-RE, 2-La) has been prepared. The complexes have been characterised using multinuclear NMR and IR spectroscopy, X-ray crystallography and elemental analysis. Structural characterisation highlighted the different RE-P interactions as a result of differing Lewis acidity and ionic size across the series, hinting at the possibility of FLP-type activity. The potential reactivity of these complexes has been tested by reacting them with small molecules (H2, CO, CO2). A series of side-products (3-RE) has also been observed, isolated and characterised, featuring the incorporation of a phosphonium-aryloxide ligand.

Transformation of Arsenic from Poison into Active Site by Construction of Unique AsOx/CeO2 Interface for Stable NOx Removal.

Arsenic in the flue gas has been widely reported as a common poison for SCR catalysts; however, an appropriate coping strategy is still lacking to improve the arsenic resistance performance. Herein, a unique AsOx/CeO2 interface is constructed to transform arsenic from poison into active site with balanced acid-redox property, successfully achieving efficient NOx removal. The optimized AsOx/CeO2 exhibits high NOx removal efficiency, four times that of the As-poisoned V2O5/TiO2 catalyst, and even comparable to the state-of-the-art SCR catalysts. It was found that the As-O-Ce interfacial sites in oxygen-bridged As dimers on CeO2 can provide both Lewis acid sites and active lattice oxygen species, enhancing the adsorption and activation of NH3 to form key -NH2 intermediates, thereby facilitating the NH3-SCR reaction. More surprisingly, a thin CeO2 layer on the top of V2O5/TiO2 can capture arsenic to protect catalysts from arsenic attacking, which improves the catalytic activity to 2.8 × 10-7 mol g-1 s-1, even higher than that of fresh V2O5/TiO2 (2.0 × 10-7 mol g-1 s-1). Therefore, this strategy provides new ideas not only for designing antipoisoning SCR catalysts but also a feasible solution for the stable operation of commercial SCR catalysts in arsenic-containing flue gas.

Passivation of Perovskite Solar Cells with Natural Flavors: Roles of Hydrogen Bonding in Ion Migration and Moisture Resistance.

The passivation strategy is considered to be an essential approach for enhancing the efficiency and stability of perovskite solar cells (PSCs). Herein, based on density functional theory calculations and ab initio molecular dynamics simulations, we investigated the ion migration and moisture stability for MAPbI3 passivated with a Lewis base represented by natural molecules: cinnamaldehyde (CA) and anethole (AT). The results reveal that hydrogen bonding in different forms plays a significant role in both ion migration and moisture stability for surface passivation. The passivation inhibits ion migration by enhancing intrinsic hydrogen bonding through space compression effect, leading to a boosted activation barrier and a reduced rate by up to 3-10 orders of magnitude. Passivations prevent in-depth water infiltration and diminish the disturbance of the lattice by water. In addition to the familiar water-shielding behavior, the water-locking effect induced by the intermolecular hydrogen bonding chains was observed. The experimental results of durable water stability and alleviated hysteresis for passivated PSCs fully confirmed the theoretical study. The established mechanism provides valuable guidance to deal with troublesome ion migration and moisture resistance in stable and efficient PSCs.

Synthesis of Aminodiborane From Ammonia Borane Using Different Lewis Acids: A Competing Reaction for Diborane Formation with Boron Trihalides (BX3, X=Cl, Br)

AbstractThe dehydrogenation of ammonia borane in the presence of a variety of Lewis acids such as ICl, IBr, Br2, CuCl2, AlCl3, GaCl3, InCl3, and [Ph3C]BF4 at a concentration of 7.5 mol % was effective in selectively producing aminodiborane (μ‐NH₂B₂H₅, ADB) at 80 °C. Compounds such as ICl, IBr, Br2, AlCl3, and GaCl3 at the same concentration could also generate ADB at lower temperatures of 35 °C and 50 °C. In contrast, BX3 (X=Cl, Br) at the same concentration of 7.5 mol % was found to give exclusively B2H6. Further, selective synthesis of diborane or ADB was achieved by adjusting the stoichiometry of the boron trihalides. A concentration of 7.5 mol % (upto 1 equivalent) of BBr3 favored the formation of B2H6, while 1 mol % BBr3 predominantly yielded ADB. Interestingly, both ADB and B2H6 facilitated the reduction of acetanilides. A mechanism has been proposed for both diborane and ADB formation using these Lewis acids.

Low-Temperature Borylation of C(sp3)-O Bonds of Alkyl Ethers by Gold-Metal Oxide Cooperative Catalysis.

Since ether moieties are often found not only in petrochemical products but also in natural organic molecules, the development of methods for manipulating C-O bonds of ethers is important for expanding the range of compound libraries synthesized from biomass resources, which should contribute to the goal of carbon neutrality. We report herein that gold nanoparticles supported on Lewis acidic metal oxides, namely α-Fe2O3, showed excellent catalytic activity for the reaction of dialkyl ethers and diborons, which enables the conversion of unactivated C(sp3)-O bonds to C(sp3)-B bonds at around room temperature. Various acyclic and cyclic ethers as well as a series of diborons participated in the heterogeneous gold-catalyzed borylation of unactivated C(sp3)-O bonds, to give a series of alkylboronates in high yields. Mechanistic studies corroborated that the present borylation of C(sp3)-O bonds of dialkyl ethers proceeded at the interface between gold nanoparticles and Lewis acidic metal oxides. Furthermore, adsorption IR measurements supported the notion that strong Lewis acid sites were generated at the boron atom of diborons adsorbed at the interface between Lewis acidic metal oxides and gold nanoparticles, which enabled us to ensure that the cooperation of gold nanoparticles and Lewis acidic metal oxides was responsible for the efficient transformation of unactivated C(sp3)-O bonds in ethers under mild conditions. This novel reaction technology which is specific to heterogeneous catalysts enables the activation of stable C(sp3)-O bonds of oxygenated chemical feedstock, which is beneficial for the sustainable synthesis of value-added organoboron compounds.

Theoretical Mechanism of Rh-Containing Species Catalyzing the Hydrogenolysis of Lignin Model Compounds Using -CαO-H and -Cα-H Groups as Superior H-Sources.

The hydrogenolysis of lignin model compounds (MCs) into high-value chemicals has received increasing attention, but their catalytic reaction mechanisms are not yet very clear. Here, we report the reaction mechanisms of the hydrogenolysis of MC into 4-acetylanisole (AAL) and guaiacol (GAL) catalyzed by LRuCl3 (L = 4'-(4-methoxyphenyl)-2,2':6',2″-terpyridine) with MC, H2, and 1-phenylethan-1-ol (PEO) as the H-sources in aqueous solution with the Bro̷nsted base (NaOH), at the M06/def2-TZVP, 6-311++G (d,p) theoretical level, namely, RS-Self, RS-H2, and RS-PEO, respectively. After dissociation in NaOH aqueous solution, the LRuCl3 compound can form a stable complex LRh (OH)3 as the initial catalytically active species. Their rate-determining steps are related to the cleavage of the -CαO-H bond in both RS-Self-and RS-PEO, whereas it is associated with the heterolysis of the H-H bond in RS-H2. From NaOH aqueous solution, the OH- ligand of LRh(OH)3 promotes the cleavage of the -CαO-H bond with MC and PEO as H-sources, whereas it advances the heterolysis of the H-H bond with H2 as the H-source, owing to its strong Bro̷nsted basicity. Furthermore, the Rh center of LRh(OH)3 mediates the cleavage of the -Cα-H bond, because of its Lewis acidity. The reaction activity lowers as RS-Self > RS-PEO ≫ RS-H2, which is positively dependent on the protonation degree of the departing H atom. Compounds containing both -CαO-H and -Cα-H groups can act as effective donors for H-sources. In the meantime, the stronger the electron-withdrawing groups they contain, the more pronounced the protonation of the -CαO-H group and the higher the reaction activity in providing H-sources. The present results provide insights into utilizing lignin's own functional groups as a hydrogen source for high-value conversion.

Improving CO2 desorption performance in monoethanolamine solutions by adding titanium pyrophosphate catalyst

Catalytic CO2 desorption has emerged as a crucial strategy for enhancing the efficiency of CO2 capture and reducing energy requirements, thereby advancing chemical absorption methods. This study examines the catalytic effectiveness of titanium pyrophosphate (TiP2O7) in improving monoethanolamine (MEA)-based CO2 absorption and desorption processes, comparing its performance with other titanium-based catalysts, including titanium dioxide (TiO2), titanium tetrahydroxide (TiO(OH)2), and titanium carbide (TiC). In TiP2O7, Ti ions function as Lewis acid sites by accepting electron pairs (LASs), P2O74− anions act as proton carriers, facilitating rapid proton transfer as Lewis base sites (LBSs), and active hydroxyl groups on the surface, resulting from water molecule dissociation or the deprotonation reaction, function as Brönsted acid sites (BASs). These sites work synergistically to accelerate CO2 desorption. TiP2O7 outperforms the other catalysts tested, primarily due to its optimal Brönsted/Lewis (B/L) ratio. This characteristic is particularly advantageous for regenerating RNHCOO−, as the reaction predominantly follows a hydrogen transfer pathway facilitated by the BASs. Consequently, TiP2O7 enhances the CO2 desorption rate by 41.5% at a desorption temperature of 91 °C, while simultaneously reducing the relative heat duty by 13% compared to processes without catalysts.

Revealing the Overlooked Catalytic Ability of γ-Al2O3: Efficient Activation of Peroxymonosulfate for Enhanced Water Treatment.

Activated alumina (γ-Al2O3) is one of the few nanomaterials manufactured at a ton-scale and successfully implemented in large-scale water treatment. Yet its role in advanced oxidation processes (AOPs) has primarily been limited to functioning as an inert carrier due to its inherently nonredox nature. This study, for the first time, presents the highly efficient capability of γ-Al2O3 to activate peroxymonosulfate (PMS) for selectively eliminating electron-rich organic pollutants in the presence of Cl-. Through experimental and theoretical analysis, we revealed that γ-Al2O3, characterized by uniquely strong Lewis acid sites, enabled robust inner-sphere complexation between PMS and Al(III) sites, triggering the oxidation of Cl- to free chlorine through a distinctive, low-energy-barrier Eley-Rideal pathway. Such a unique pathway resulted in a 42.7-fold increase in free chlorine generation, culminating in a remarkable 145.9-fold enhancement in the degradation of carbamazepine (CBZ) compared with the case without γ-Al2O3. Furthermore, this catalyst exhibited high oxidant utilization efficiency, stable performance in real-world environmental matrices, and sustained long-term activation for over 1206 bed volumes (BV) with a CBZ removal rate exceeding 90% in fixed-bed experiments. These favorable features render γ-Al2O3 an extremely promising nanomaterial for sustainable water treatment initiatives.

Shielding Fluoride Ion Basicity through Diurea Coordination for Nonaqueous Fluoride Shuttle Batteries

AbstractThe strong basicity of fluoride ions leads to detrimental nucleophilic attack on organic components in the electrolytes, such as β‐hydrogen elimination reactions with organic cations and solvents, converting “naked” F− into corrosive and unstable bifluoride (HF2−) ions. These reactions significantly constrain the choice of suitable solvents and salts to develop electro(chemical) stable fluoride ion electrolytes. In this work, we replaced the triple water ligands typically present in industrial organic fluoride salts with dual 1,3‐diphenylurea (DPU) coordination via hydrogen bonding interaction. This modification successfully suppressed the Lewis basicity of fluoride ions, providing long‐term chemical stability (over 1000 hours) across a wide range of aprotic solvents, a broadened electrochemical stability window (−2.5–0.9 V vs. Ag+/Ag) and high ionic conductivity (1.7 mS cm−1) at room temperature. Additionally, the weaker hydrogen bonding in F−‐DPU coordination, compared to the conventional boron‐based anion acceptor (AA) strategy that relies on intensive Lewis acid‐base interactions, facilitates faster (de)fluorination kinetics at the electrode. The proposed room temperature fluoride ion batteries sustain improved electrochemical performance by pairing with the Pb‐PbF2 anode and BiF3 or Ag cathode.

Aminoborate-Catalyzed Reductive Counterreactions for Oxidative Electrosynthetic Transformations.

Electrooxidative transformations frequently rely on proton reduction as the terminal electron sink. However, this cathodic counterreaction can be slow in organic solvents and can operate at reducing potentials that are incompatible with catalysts and reagents needed for oxidative reactions. We report aminoborate adducts as redox mediators for proton reduction that operate at mild reducing potentials. This reliable cathodic couple ultimately enables successful oxidative organic transformations, including chlorodeborylation, developed herein, and Cu-catalyzed Chan-Lam coupling, reported previously by our group. Pyridinium borate adducts formed during electrooxidative chlorination of aryl trifluoroborates serve as easily reduced complexes (-1.1 V vs Fc/Fc+) to catalyze proton reduction. Reactions that promote the formation of borate adducts result in high yields, operate at low cell potentials, suppress aryl trifluoroborate decomposition, and mitigate electrode passivation. These studies illustrate the utility of Lewis acid-base complexes in cathodic counterreactions and underscore the importance of developing both anodic and cathodic reactions in electrosynthesis.

Unveiling the influence of open metal sites in quasi ZIF-67 for eco-friendly catalysis of solvent-free aldehyde cyanosilylation

Quasi metal–organic frameworks (Q-MOFs) containing a high density of open metal centers are considered as an effective method of expanding the effectiveness of defective MOF-based catalysts. To achieve this, quasi ZIF-67 (Q-ZIF-67), having large scale structural defects in the framework, is produced through partial deligandation of ZIF-67 under controlled thermal treatment at 310 °C in air. This generates many unsaturated cobalt centers as Lewis acid sites, and results in the coexistence of micro and meso-pores within the Q-ZIF-67 network. Subsequently Q-ZIF-67 was employed in the catalytic cyanosilylation of benzaldehyde with trimethylsilyl cyanide, resulting in the corresponding cyanohydrin within 30 min under solvent free-conditions in air at 40 °C and room temperature with TOF values of 1.62, 1.53 min−1, respectively. The related cyanohydrin product was identified via 1H NMR. Importantly, Q-ZIF-67 displayed a highly efficient heterogeneous Lewis acid catalyst for the cyanosilylation of benzaldehyde compared to the pristine ZIF-67 and related cobalt oxide. Furthermore, investigating the impact of the electron-donating and electron-withdrawing para-substitutions on benzaldehyde revealed that electron-withdrawing groups are suitable for nucleophilic reactions. It was also observed that there was no significant decrease in catalytic activity after five catalytic runs. Thus, the Q-ZIF-67 has considerable potential as environmentally friendly catalyst for wide range of practical application in aldehyde cyanosilylation reactions.

Innovative Ultrasound‐Assisted Synthesis of Isoxazolo[5,4‐b]Pyridines from Aryl Glyoxal, 5‐Aminoisoxazoles, and Malononitrile in Acetic Acid as a Solvent and Catalyst

AbstractIn this work, a novel strategy for the straightforward synthesis of isoxazolo[5,4‐b]pyridines from a one‐pot reaction of aryl glyoxal, 5‐aminoisoxazoles, and malononitrile under ultrasound (US) irradiation is described. In the reaction, acetic acid has a dual role as solvent and catalyst. The advantages of this reaction include easy purification of products, raw materials with easy access, short reaction time, high efficiency, and green conditions by utilizing ultrasound irradiation as an energy source and using acetic acid as solvent and Lewis acid. The synthesis achieved high yields of isoxazolo[5,4‐b]pyridines with a broad substrate scope, successfully producing twelve diverse derivatives. The methodology capitalizes on the benefits of sonochemistry, which accelerates reaction rates and improves selectivity while minimizing waste. The proposed mechanism involves a series of reactions including Knoevenagel condensation, Michael addition, and subsequent cyclization processes. This approach not only streamlines the synthesis of complex heterocycles but also aligns with environmentally friendly practices.

Efficient CeVO4/SnO2 and CeVO4/sulfated-SnO2 catalysts with high SO2 resistance for selective catalytic reduction of NOx with NH3: Influence of acid sites

Developing eco-friendly catalysts with high NOx removal efficiency and SO2 resistance in a wide temperature range is crucial. A series of efficient CeVO4/sulfated-SnO2 (CeV/Sn-S) and CeVO4/SnO2 (CeV/SnO2) catalysts were developed, and the optimal mass fraction of CeVO4 was 9 wt%. 9 %CeV/SnO2 and 9 %CeV/Sn-S achieved over 90.0 % NOx conversion at 220–385 and 240–430 °C, respectively, and they both showed notable SO2 resistance. CeV, 9 %CeV/SnO2 and 9 %CeV/Sn-S displayed different acid sites and SO2 adsorption capabilities. CeV exhibited low surface acidity, primarily Brønsted acidity. The introduction of SnO2 enhanced Lewis acidity, while sulfated SnO2 addition increased both Lewis and Brønsted acidity, and reduced SO2 adsorption, which benefited to the SO2 resistance. 9 %CeV/Sn-S had more lattice defects, a lager surface area, and higher Ce4+ and V5+ ratios than 9 %CeV/SnO2, indicating a stronger interaction between CeVO4 and sulfated SnO2. Then, 9 %CeV/Sn-S catalyst’s strong NH3 adsorption and moderate redox properties contributed to its higher NOx conversions and N2 selectivity above 330 °C, along with a broader operational window. Both Eley–Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms were observed in these catalysts. However, the presence of sulfates on 9 %CeV/Sn-S limited NOx adsorption, thereby reducing the contribution of L-H mechanism. The 9 %CeV/SnO2 catalyst’s strong Lewis acidity and abundant adsorbed NOx species favored the L-H mechanism, resulting in its higher NOx conversion below 250 °C compared to 9 %CeV/Sn-S. This work contributes to sharpening comprehension for the influence of acid sites and steering the design of novel SCR catalysts for efficient NOx abatement in practical applications.

Insight into the reaction route and the effect of Brønsted and Lewis acid for alkylation of 5-Hydroxymethylfurfural

5-Hydroxymethylfurfural (HMF) can be upgraded to ether as fuel or fuel additives through conversion of the hydroxyl and aldehyde groups. The two groups are always involved in different catalytic reactions, such as etherification, acetalization, hydrogen transfer reduction, and even ring-opening reactions. This makes the etherification upgrading of HMF with high selectivity to desired product a great challenge. In the present wok, transformation of HMF in isopropanol was systematically investigated over different catalysts with Brønsted acid and Lewis acid sites. The effect of catalytic sites on product distribution and selectivity was studied. Moreover, several products, such as 5-isopropoxymethylfurfural, 5-isopropoxymethylfurfuryl alcohol, 5-isopropoxymethylfurfuryl alcohol, and 2,5-furandimethanol, were obtained with high selectivity, and the conversion pathway of HMF with alcohols on different catalytic sites was revealed under different catalytic conditions. The transformation of HMF to furan triether products over multi-site catalyst was realized for the first time based on the proposed reaction pathway with excellent activity and selectivity.

Surface reaction mechanism of ZSM-5(3T)@NH2-MIL-53(Al) core-shell catalyst for dimethyldichlorosilane synthesis

Dimethyldichlorosilane is one of the most important basic monomers in the silicone industry. It is also can be recovered through by-products disproportionation reactions during synthesis. This paper investigated the reaction mechanism of ZSM-5(3T)@NH2-MIL-53(Al) catalyst, constructed by combining 3T cluster ZSM-5 zeolite and NH2-MIL-53(Al), and the modified AlCl3/ZSM-5(3T)@NH2-MIL-53(Al) catalyst in the disproportionation preparation of (CH3)2SiCl2. The M06-2X/def2-TZVP hybrid functional method from the Minnesota series was used to calculate the energies of all reactants, transition states, and products in the disproportionation preparation of (CH3)2SiCl2 reaction systems for five active sites (before AlCl3 loading) and one active site (after AlCl3 loading), respectively. Additionally, ZPE corrections were applied at the same computational level. The results of structural, energy, vibrational frequency, Intrinsic Reaction Coordinate (IRC)values, bond order, Electron Localization Function (ELF), and Localized Orbital Locator (LOL) analyses were matched. The results indicated that the Lewis acid catalytic active centers obtained after AlCl3 loading enhanced the catalytic performance of AlCl3/ZSM-5(3T)@NH2-MIL-53(Al).