Reaction Yield Research Articles

Synergistic Coordination and Surface Plasmon Resonance of Quantum Dots in Enhancing Photocatalytic Hydrogen Evolution.

Recent studies have revealed that the integration of metal nanoparticles (NPs) with photocatalysts allows the metal NPs to serve as cocatalysts, significantly enhancing reactant efficiency near nanostructures through the surface plasmon resonance (SPR) effect. On this basis, we synthesized highly reactive FePt quantum dots (FePt QDs) with tailored configurations, manipulating the Pt coordination environment and combining FePt QDs with ultrathin two-dimensional nickel metal-organic layer (Ni-MOL) nanosheets. X-ray absorption fine spectroscopy (XAFS) confirmed the distinctive Pt-Fe configuration after photoactivation. The optimized loading amount of FePt QDs led to a hydrogen evolution reaction (HER) yield of 113 mmol·g-1·h-1 after activation, with the catalyst remaining stable over five cycles. The improved reaction efficiency stemmed from Pt coordination adjustments and a localized SPR effect, supported by ultraviolet-visible (UV-vis), infrared (IR), Raman, and XAFS characterizations. A comparative analysis was conducted with Ni-MOL deposited with platinum NPs, further underscoring the distinct advantages of FePt QDs and corroborating by density functional theory (DFT) calculations, which revealed favorable d-band center properties. These findings offer a promising avenue for the development of highly efficient and stable nanoalloy photocatalysts.

From lignin-derived monomers to 1,4-cyclohexanediol via a two steps Dakin oxidation and hydrodeoxygenation reaction

Lignin is the largest renewable source of aromatic building blocks in nature and has great potential as a starting material for the production of bulk or functionalized aromatic compounds, providing a suitable alternative to widely used petroleum-derived chemicals. In this work, we present a novel 1,4-cyclohexanediol (CHDO) preparation from lignocellulose. In contrast to conventional methods, this pathway has taken the lignin-degrading monomers as a starting point, and flexibly employs a series of oxidative and catalytic reactions to achieve the preparation of CHDO. The proposed pathway consists of a two-step chemical process to efficiently obtain high yields of CHDO from lignocellulose. The first step is the oxidation of lignin-derived monophenols to p-hydroxyl phenolic compounds using the Dakin oxidation reaction (yield>80 %), and finally the de-functionalization and hydrogenation of the resulting monomers using the hydrodeoxygenation (HDO) reaction.

Tetrabutylammonium Hydrogen Sulfate (TBAHS) Catalyzed Microwave-Assisted Synthesis of 3,4,5,6,7,9-Hexahydro-1H-xanthene-1,8-(2H)-dione Derivatives and its Biological Study

In this study, a facile and eco-friendly synthesis of novel 3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione derivatives using tetrabutylammonium hydrogen sulfate (TBAHS) as a catalyst in the microwave reactor is presented. The reaction involved the condensation of aromatic aldehydes with 1,3-cyclohexanedione in ethanol as solvent, offering significant advantages in terms of reaction rate, yield and purity. The use of TBAHS as catalyst in conjunction with microwave irradiation facilitated the formation of the target xanthene derivatives in remarkably short reaction times. Moreover, Monowave 50 microwave reactor provided precise control over reaction parameters, enabling rapid optimization of reaction conditions. Further these synthesized compounds were systematically evaluated for their antibacterial, antituberculosis and antioxidant activities.

Microwave-Assisted Synthesis of Bis-(Hydroxybenzylidene)-Cycloalkanones via Acid Catalyzed Claisen-Schmidt Condensation

In the present study, bis-(hydroxybenzylidene)cycloalkanone derivatives were synthesized by Claisen-Schmidt condensation using cycloalkanones and arylaldehydes in the presence of HCl as an acid catalyst. The synthetic reaction was carried out under microwave irradiation. The structure of the synthesized compounds was determined by UV, IR, 1H NMR spectroscopic methods. The obtained reaction yields were not optimal due to the self-polymerization of p-hydroxybenzaldehyde in an acid solution.

An Automated Electrochemical Flow Platform to Accelerate Library Synthesis and Reaction Optimization

Automated batch and flow reactors are well‐established for high throughput experimentation in both thermal chemistry and photochemistry. However, the development of automated electrochemical platforms is hindered by cell miniaturization challenges in batch and difficulties in designing effective single‐pass flow systems. In order to address these issues, we have designed and implemented a new, slug‐based automated electrochemical flow platform. This platform was successfully demonstrated for electrochemical C‐N cross‐couplings of E3 ligase binders with diverse amines (44 examples), which were subsequently transferred to a continuous‐flow mode for confirmation and isolation, showing its applicability for medicinal chemistry purposes. To further validate the versatility of the platform, Design of Experiments (DoE) optimization was performed for an unsuccessful library target. This optimization process, fully automated by the platform, resulted in a remarkable 6‐fold increase in reaction yield.

An Automated Electrochemical Flow Platform to Accelerate Library Synthesis and Reaction Optimization.

Automated batch and flow reactors are well-established for high throughput experimentation in both thermal chemistry and photochemistry. However, the development of automated electrochemical platforms is hindered by cell miniaturization challenges in batch and difficulties in designing effective single-pass flow systems. In order to address these issues, we have designed and implemented a new, slug-based automated electrochemical flow platform. This platform was successfully demonstrated for electrochemical C-N cross-couplings of E3 ligase binders with diverse amines (44 examples), which were subsequently transferred to a continuous-flow mode for confirmation and isolation, showing its applicability for medicinal chemistry purposes. To further validate the versatility of the platform, Design of Experiments (DoE) optimization was performed for an unsuccessful library target. This optimization process, fully automated by the platform, resulted in a remarkable 6-fold increase in reaction yield.

Computational Investigation of the Ru‐Mediated Preparation of Benzothiazoles From N‐Arylthioureas: Elucidation of the Reaction Mechanism and the Origin of Differing Substrate Reactivity

ABSTRACTSynthesis of novel benzothiazoles via intramolecular CS bond formation reactions is increasingly being explored since they have been found in a wide range of natural products and pharmaceutical agents. Sharma et al. reported the ruthenium‐catalyzed preparation of novel benzothiazole derivatives from N‐arylthiourea precursors, with a range of reaction yields and selectivity being observed. We have employed a density functional theory‐based computational model to investigate the reaction mechanism leading to the benzothiazole product and help uncover the origin of the differing experimental yields and substrate specificities. We proposed a modified mechanistic scheme where the rate‐determining step to be the synchronized breaking of the peroxide bond of the oxidizing agent with the concomitant proton‐coupled electron transfer from the haloarene urea and a Ru‐bound water molecule, not electrophilic RuC bond activation. Evidence for this being the rate‐determining step is (a) the barrier is consistent with a lack of kinetic isotope effects associated with the ortho‐H atom and (b) the computed rate‐determining barriers for 10 N‐arylthiourea substrates show good correlation with the observed yield.

A Structural, Spectroscopic and DFT Theoretical Comparison of the cis and trans Isomers of a Cyclohexasilane

AbstractWe report a synthesis of the trans and cis isomers of 1,4‐di‐tert‐butyl‐2,2,3,3,5,5,6,6‐octamethyl‐1,4‐diphenylcyclohexasilane (3), together with the solid‐state structure of cis‐3. Both isomers were characterized using multinuclear NMR and UV spectroscopies and were compared based on these data, together with DFT calculations. Remarkably, we found that both isomers of 3 showcase redshifted UV maxima when compared with other known cyclosilanes. To explain this, the theoretical calculations show that the transitions involved in the excited states of trans‐3 and cis‐3 have, in addition to the expected σ conjugation component of the Si6 ring, significant π contributions of phenyl substituents. The results presented herein show the effect of the substituent's electronic properties regarding reactivity of intermediates, reaction yield, identity, and electronic properties of novel silicon‐containing molecules.

In Silico Models for Prediction of Methanol Yield in CO2 Hydrogenation Reaction Using Cu-Based Catalysts

In Silico Models for Prediction of Methanol Yield in CO2 Hydrogenation Reaction Using Cu-Based Catalysts

Solvent-free mechanosynthesis of Schiff bases derived from thiadiazole with potential application in sensing ionic species and NLO applications

In this work, we report the solvent-free mechanosynthesis of three Schiff bases (SBs) derived from 1,3,4-thiadiazole covalently bonded to indole (Th-In), quinoline (Th-Qn) and triphenylamine (Th-TPA) groups. This green chemistry method showed a drastic reduction in reaction time and avoidance of solvents for obtaining SBs, with good reaction yields. The molecular structures of SBs were investigated by computational chemistry calculations, with global reactivity parameters indicative of electron acceptor behavior, estimation of frontier molecular orbitals, and their theoretical band gaps of 3.49 and 3.4 eV for Th-In and Th-Qn, respectively, and the lowest of 299 eV for Th-TPA. To evaluate the possible NLO response, the hyperpolarizabilities (β) were also estimated, which are several orders of magnitude higher than the urea value used as a reference. The absorption and emission spectra were calculated using TD-DFT. These results showed a larger redshift for Th-TPA, with possible charge transfer processes more intense than those obtained for Th-In and Th-Qn. The photophysical properties of the Schiff bases were determined, with band gap values for Th-In, Th-Qn, and Th-TPA of 2.53, 2.66, and 2.39 eV in solution and 2.77, 2.26, and 2.21 eV in film, respectively. When the SBs were evaluated as potential naked-eye colorimetric chemosensors, colorimetric changes were observed in Fe2+, Fe3+, Pb2+, Cu2+, and Ag+ ions, with Ag+ being the most promising. Z-scan was used to evaluate the nonlinear response of the SBs and showed saturable absorber behavior with self-focusing processes. Cyclic voltammetry was used to determine the electrochemical band gaps, which were 2.70, 2.71, and 1.98 eV for Th-In, Th-Qn, and Th-TPA, respectively. Th-TPA exhibits superior optical and electrical properties among the three SBs investigated. In addition, it exhibits photochromism, which can be used in conjunction with its other properties in NLO and sensor applications.

Chemical Graph-Based Transformer Models for Yield Prediction of High-Throughput Cross-Coupling Reaction Datasets.

The chemical reaction yield is an important factor to determine the reaction conditions. Recently, many data-driven models for yield prediction using high-throughput experimentation datasets have been reported. In this study, we propose a neural network architecture based on the chemical graphs of the reaction components to predict the reaction yield. The proposed model is the sequential combination of a message-passing neural network and a transformer encoder (MPNN-Transformer). The reaction components are converted to molecular matrices by the first network, followed by the interplay of the reaction components in the second network after adding the embeddings of the compound roles in the chemical reaction. The predictive ability of the proposed models was compared with state-of-the-art yield prediction models using two high-throughput experimental datasets: the Buchwald-Hartwig cross-coupling (BHC) and Suzuki-Miyaura cross-coupling (SMC) reaction datasets. Overall, the MPNN-Transformer models showed high prediction accuracy for the BHC reaction datasets and some of the extrapolation-oriented SMC reaction datasets. These models also performed well when the training dataset size was relatively large. Furthermore, analyzing the poorly predicted reactions for the BHC reaction dataset revealed a limitation of the data-driven yield prediction approach based on the chemical structural similarity.

Plasma Coating for Hydrophobisation of Micro- and Nanotextured Electrocatalyst Materials

The need for sustainable energy solutions is steering research towards green fuels. One promising approach involves electrocatalytic gas conversion, which requires efficient catalyst surfaces. This study focuses on developing and testing a hydrophobic octadiene (OD) coating for potential use in electrocatalytic gas conversion. The approach aims to combine a plasma-deposited hydrophobic coating with air-trapping micro- and nanotopographies to increase the yield of electrocatalytic reactions. Plasma polymerisation was used to deposit OD films, chosen for their fluorine-free non-polar properties, onto titanium substrates. We assessed the stability and charge permeability of these hydrophobic coatings under electrochemical conditions relevant to electrocatalysis. Our findings indicate that plasma-deposited OD films, combined with micro-texturing, could improve the availability of reactant gases at the catalyst surface while limiting water access. In the presence of nanotextures, however, the OD-coated catalyst did not retain its hydrophobicity. This approach holds promise to inform the future development of catalyst materials for the electrocatalytic conversion of dinitrogen (N2) and carbon dioxide (CO2) into green fuels.

Evaluation on potential application of lipase immobilized on rice husks in enzymatic glycerolysis reaction

Owing to high production cost and low reaction yield, immobilized lipase is rarely used in industrial glycerolysis. This research characterizes the performance of lipase immobilized on rice husk in glycerolysis reaction. By utilizing hexamethylenediamine (HMDA) and glutaraldehyde (GA) as coupling agents, lipase from Thermomyces lanuginosus was immobilized on oxidized rice husk (ORH). For comparison, another sample was prepared where the lipase was directly immobilized on ORH without the use of HMDA and GA. Then, monoglyceride production was performed via glycerolysis using the immobilized lipase. The FTIR analysis verify interactions on rice husk including rice husk oxidation, HMDA coupling, GA activation and lipase immobilization on rice husk. The study found that within the examined range of added lipase for immobilization (10–40 mg-protein/g-support), ORH–HMDA–GA–Lipase possessed superior outcomes in terms of protein loading, immobilization yield, and recovered glycerolysis activity compared to ORH–Lipase. Besides, ORH–HMDA–GA–Lipase exhibits better storage stability (60°C, 44.9 %) and higher reusability (90.0 % monoglyceride yield at the 8th cycle) against ORH–Lipase. The results confirm satisfying performance of the prepared immobilized lipase in glycerolysis and highlight its enhancements facilitated by coupling agents.

Green synthesis of glycolic acid through the electrocatalytic reduction of oxalic acid over black TiO2: An experimental and theoretical study

Herein, we present the electrocatalytic four-electron hydrogenation of oxalic acid into glycolic acid using black TiO2 as an electrocatalyst. Oxalic acid is an abundant compound found in several sources of organic waste. The results showed a high selectivity of black TiO2 toward glycolic acid, with the formation of glyoxylic acid being the rate-limiting step (glyoxylic acid is the two-electron intermediate). The highest Faradaic efficiency (FE) of 69.6% ± 8.3% was achieved at 10.2 mA cm−2 in 4 h of electrolysis using an H-type cell operated at room temperature, with 50.2% ± 3.8% of oxalic acid conversion (degradation kinetic constant k = 0.0042 ± 0.0001 min−1), 58.8% ± 7.0% of reaction yield and 1.2 ± 0.18 g L−1 of glycolic acid production. A theoretical model of black TiO2 coming from anatase TiO2 was implemented by introducing Ti3+ defects, which gave black TiO2 the theoretical capability to easily transform oxalic acid into glycolic acid as experimentally observed. The reaction mechanism was supported and described in detail by density functional theory calculations, which revealed that surface Ti3+ states were the main catalytic sites. This is the first time that a detailed step-by-step mechanism at the atomic level has been proposed for this electrocatalytic reaction, which represents a valuable contribution to the understanding of this process of high energy/environmental interest. This is also the first time that black TiO2 has been used as an electrocatalyst for this sustainable process.

Al2O3 Concentration Effect on Deep Hydrodesulfurization of 4,6-Dimethyldibenzothiophene over NiWS/Al2O3-ZrO2 Catalysts.

The Al2O3 concentration effect over NiWS/Al x Zr100-x catalysts was investigated for deep hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT). The sol-gel method changed the wt % Al2O3 concentrations used to synthesize the Al x Zr100-x supports. The NiWS/Al x Zr100-x catalysts were prepared with ammonium metatungstate hydrate and nickel(II) nitrate hexahydrate by sequential incipient impregnation, calcination, and H2S/H2 activation. The catalytic evaluation data fit a pseudo-first-order trend in the 4,6-DMDBT HDS reactions. In the oxide phase, the catalysts presented Ni and W species in tetrahedral (td) and octahedral (oh) coordination, with the oh species prevailing as a function of the Al2O3 amount. The lower amount of Al2O3 can facilitate the "Type II" NiWS phase formation by weakening the interaction of the W-O-Al bond and promoting W and Ni species sulfidation. In the sulfide phase, catalysts with (oh) coordination and surface WO X species promote the formation of WS2 and NiWS species during the catalyst activation step. This species favors the reaction yield, where the hydrogenation route is predominant, with the highest initial reaction rate using the NiWS/Al25Zr75 catalyst. A direct correlation was found between high hydrogenation/hydrogenolysis ratio values and low Al2O3 concentrations.

Three-component Synthesis of Tetrahydrobenzo[b]pyrans Using MMWCNTs-PEG-IL as a Novel Magnetic Immobilized Ionic Liquid

Introduction: A novel immobilized imidazolium type ionic liquid was synthesized using poly(ethylene glycol) (PEG) functionalized magnetic multi-walled carbon nanotubes. This immobilized ionic liquid (MMWCNTs-PEG-IL) was characterized by FT-IR, VSM, XRD, FE-SEM and EDX analysis. Method: Then, it was used as a magnetic catalyst in a three-component reaction to yield tetrahydrobenzo[b]pyran derivatives. First, optimized reaction conditions were investigated. A mixture of containing dimedone (1 mmol), malononitrile (1 mmol), benzaldehyde (1.2 mmol) and MMWCNTs-PEG-IL (0.03 g) in H2O/EtOH (5 mL) was stirred at 70 °C. After completion of the reaction, the mixture was cooled. Results: Then, an external magnet was used to separate the magnetic catalyst. This method has many advantages including high reaction yields, high TOFs, using non-toxic solvents, easy handling of catalyst, simple separation of catalyst from reaction medium and short reaction times. Conclusion: Also, the reusability of the magnetic catalyst has been investigated in 7 runs without serious loss of reaction yield.

Mass transfer-enhanced platform for heterogeneous dual organocatalysis to boost yield and diastereoselectivity in enantioselective Michael/benzoin cascade reaction

Mass transfer limitation and tedious anchoring of multiple expensive chiral organocatalysts are the key bottlenecks in heterogeneous asymmetric cascade/tandem reactions, leading to high-cost processes with low catalytic performances. In this paper, two chiral organocatalysts, including (S)-diphenylprolinoltrimethylsilyl ether (ProTMS) and N-heterocyclic carbenes (NHC), are simultaneously immobilized to hollow mesoporous polystyrene nanospheres (HMPNs) in one-pot via Friedel-Crafts alkylation to afford supported dual organocatalysts (ProTMS&NHC@HMPNs) at low cost. The catalyst possesses the spherical morphology with a hollow interior and a thin mesopore-abundant shell, providing suitable environments for reactants to quickly access to the catalytic sites of NHC and ProTMS. The side reactions caused by limited mass transfer are effectively suppressed, and superior yields (70–92 %) and diastereoselectivities (dr = 3:120:1) to homogeneous catalysis are achieved in heterogeneous Michael/benzoin cascade reaction. Overall, the mass transfer-enhanced platform for efficient heterogeneous dual organocatalysis is developed to boost yield and diastereoselectivity in asymmetric cascade reactions.

Facile synthesis and antifungal evaluation of hypervalent organoantimony(III) and organobismuth(III) thioates with tridentate C,N,C-coordinating ligands.

In the present work, a series of organometallic thioates bearing a 5,6,7,12-tetrahydrodibenzo[c,f][1,5]azastibocine or -azabismocine framework were synthesized through the cross-coupling reactions of the corresponding halide precursors with thiols and disulfides at room temperature. The former transformation can be achieved under additive-free conditions, and mild dithiothreitol (DTT) is the only additive in the latter. Both methods feature simple operation, a broad substrate scope, and good reaction yields. Antifungal assays showed that the synthesized organobismuth(III) thioates possess significantly higher antibiotic activity against Candida albicans than clinical fluconazole, while the inhibitory effects of Sb-sulfenylated products are low to negligible. Furthermore, the antibiofilm potential of such Bi-S bond-containing compounds was discovered as well.

Enhanced Efficiency of Amide‐Substituted Quinuclidine‐Boranes as Hydridic Hydrogen Atom Transfer Catalysts for Photoinduced Hydroalkylation of Unactivated Olefins†

Comprehensive SummaryAn amide‐substituted quinuclidine‐borane has been identified as a more efficient hydridic hydrogen atom transfer (HAT) catalyst for the hydroalkylation of unactivated olefins under visible‐light irradiation. 1H NMR titration experiments reveal that the amide moiety of the quinuclidine‐borane catalyst forms stronger hydrogen bonds with the carbonyl substrates, thereby improving the reaction yields. Furthermore, it was found that the reaction yields correlate well with the association constant between the quinuclidine‐borane catalyst and the carbonyl substrate. A scale‐up reaction using a continuous‐flow photoreactor has also been demonstrated.

Deprotective Lossen rearrangement: a direct and general transformation of Nms-amides to unsymmetrical ureas.

Ureas stand out as potent pharmacophores in drug development, rendering them a prime focus for synthesis. Herein, we present an appealing entry point for urea synthesis from protected amines (Nms-amides) and relying on a Lossen-type rearrangement process as an elegant example of deprotective functionalisation. The method developed exhibits an exceptionally broad tolerance towards various protected amines, encompassing numerous drug derivatives, and delivers high reaction yields.