Optimal Reaction Conditions Research Articles

Synthesis of PEI Grafted Poly (Ionic Liquid)s: Optimization and Kinetics Modeling of Effective CO2 Fixation Reactions

AbstractFixing the greenhouse gas CO2 through epoxide helps to mitigate worldwide ecological troubles. The applications of metal‐free and solvent‐free catalysts remain a challenge for CO2 catalytic conversion. In this work, an array of quaternary ammonium salts derived from polyethyleneimine with hydroxyl groups ([PEI‐GDMAB‐Cn]Br) were constructed by the reaction of branched PEI with a molecular weight of 10000 and glycidyl alkyl dimethylammonium bromide. A range of experiments were designed to demonstrate that [PEI‐GDMAB‐Cn]Br can be considered as a valid metal‐free and solvent‐free homogeneous catalyst for the CO2‐epoxide cycloaddition reaction. Among of [PEI‐GDMAB‐Cn]Br, [PEI‐GDMAB‐C18]Br catalyzed the model reaction of CO2 and epichlorohydrin under optimized reaction conditions (T=80 °C, 1.0 atm CO2, catalyst 1 mol%, ECH 15 mmol, 16 h) and the conversion achieved at 97.5 %. Moreover, the catalyst exhibited stable reusability and broad substrate applicability, which was used in the following cycle succinctly, because of self‐separated properties by temperature control. The [PEI‐GDMAB‐C18]Br catalyzed reaction process was detected as a pseudo‐first‐order reaction after kinetic studies and an Ea was calculated to be 50.65 kJ/mol. A combinatorial catalytic mechanism of hydrogen bonding and bromide ions is suggested to explain the remarkable catalytic performance of this bifunctional catalyst.

The Development of Aptamer-Based Gold Nanoparticle Lateral Flow Test Strips for the Detection of SARS-CoV-2 S Proteins on the Surface of Cold-Chain Food Packaging

The COVID-19 pandemic over recent years has shown a great need for the rapid, low-cost, and on-site detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In this study, an aptamer-based colloidal gold nanoparticle lateral flow test strip was well developed to realize the visual detection of wild-type SARS-CoV-2 spike proteins (SPs) and multiple variants. Under the optimal reaction conditions, a low detection limit of SARS-CoV-2 S proteins of 0.68 nM was acquired, and the actual detection recovery was 83.3% to 108.8% for real-world samples. This suggests a potential tool for the prompt detection of SARS-CoV-2 with good sensitivity and accuracy, and a new method for the development of alternative antibody test strips for the detection of other viral targets.

Microkinetic Model as a Crucial Tool for Understanding Homogeneous Catalysis

Microkinetic modeling is a computational tool that allows simulating the evolution of the concentration of catalytically relevant species with time, providing a description of the catalytic system closer to the experimental. Microkinetic models have been mainly applied in organometallic catalysis as a means for validating mechanistic proposals by comparing experimental and computed rates and concentrations at a given time. However, this tool becomes very useful when studying complicated reaction mechanisms, aiding in identifying the catalyst resting state, optimizing reaction conditions or improving the catalyst design. In this Concept, we focus on these applications of microkinetic modeling through the discussion of some selected examples. In addition, we also point out some of the challenges and limitations we may face when building microkinetic models, which may explain why they are still underused.

A theoretical study on toluene oxidization by OH radical

Toluene, a prominent member of volatile organic compounds (VOCs), exerts a substantial adverse influence on both human life and the environment. In the context of advanced oxidation processes, the ·OH radical emerges as a highly efficient oxidant, pivotal in the elimination of VOCs. This study employs computational quantum chemistry methods (G4MP2//B3LYP/6-311++G(d,p)) to systematically investigate the degradation of toluene by ·OH radicals in an implicit solvent model, and validates the rationale of choosing a single-reference method using T1 diagnostics. Our results suggest three possible reaction mechanisms for the oxidation of toluene by ·OH: firstly, the phenyl ring undergoes a hydrogen abstraction reaction followed by direct combination with ·OH to form cresol; secondly, ·OH directly adds to the phenyl ring, leading to ring opening; thirdly, oxidation of sidechain to benzoic acid followed by further addition and ring opening. The last two oxidation pathways involve the ring opening of toluene via the addition of ·OH, significantly facilitating the process. Therefore, both pathways are considered feasible for the degradation of toluene. Subsequently, the UV-H2O2 system was designed to induce the formation of ·OH for toluene degradation and to identify the optimal reaction conditions. It was demonstrated that ·OH and 1O2 are the primary active species for degrading toluene, with their contribution ranking as ·OH > 1O2. The intermediates in the mixture solution after reactions were characterized using GC–MS, demonstrating the validity of theoretical predictions. A comparative study of the toluene consumption rate revealed an experimental comprehensive activation energy of 10.33 kJ/mol, which is consistent with the preliminary activation energies obtained via theoretical analysis of these three mechanisms (0.56 kJ/mol to 13.66 kJ/mol), indicating that this theoretical method can provide a theoretical basis for experimental studies on the oxidation of toluene by ·OH.

Ligand‐Free Copper(0)‐Catalyzed C−S Ullmann‐Type Cross‐Coupling Reaction: S‐Arylation of 5,4‐Disubstituted 2,4‐Dihydro‐3H‐1,2,4‐triazole‐3‐thiones

AbstractWe investigated the S‐arylation of 5,4‐disubstituted 2,4‐dihydro‐3H‐1,2,4‐triazole‐3‐thiones under ligand‐free Cu(0) catalysis employing Ullmann‐type reaction conditions. We determined optimal reaction conditions and assessed the impact of substituents in the arylating agent on the reaction progress. Notably, the presence of an electron‐withdrawing group (EWG) in the aryl halide facilitated the reaction even without a catalyst. In particular, an EWG in the para position of the aromatic ring exerted a directing effect on the leaving group, regardless of the halogen present.

Study on characteristics of toluene/chlorobenzene nitrification in different microreactors

Aromatic nitrification with mixed acid is an important industrial reaction with fast, strong-exothermic, and high-risk reaction characteristics. To investigate the promotion for the preparation of nitrotoluene (MNT) and nitrochlorobenzene (NCB), three microreactors with different structural features, namely, heart-shaped, diamond-shaped, and zigzag-shaped microreactors, are designed and fabricated. Firstly, the effects of temperature, residence time, and molar ratio on toluene (TOL) and chlorobenzene (CB) nitrification are investigated, and orthogonal experiments are further conducted to determine the optimum reaction conditions. Results showed that channel structures and the residence time τ have negligible effects on the isomers selectivity of the three microreactors, and higher reaction temperatures and mole ratios would lead to the substantial occurrence of side reactions and byproducts in the zigzag microreactor. The heart-shaped microreactor has the highest value of 91.49 % for the MNT's optimal yield, followed by the diamond-shaped and zigzag-shaped microreactors (89.91 % and 89.81 %, respectively). The heart-shaped microreactor provides the maximum amount of NCB preparation (93.95 %), while the yields of the diamond-shaped and zigzag-shaped microreactors are 91.51 % and 88.25 %, respectively. This work provides the experimental basis for the efficient preparation and industrial scale-up of aromatic nitrification in microreactors.

Microwave-assisted transesterification of sour cherry kernel oil for biodiesel production: comparison with ultrasonic bath-, ultrasonic probe-, and ohmic-assisted transesterification methods

In this study, sour cherry kernel oil was converted to biodiesel by microwave-assisted transesterification. Evaluations were made of several variables, namely, reaction time (1, 2, 3, 4, and 5 min), microwave power (100, 200, 300, 400, and 500 W), methanol/oil mole ratio (3, 6, 9, 12, and 15), and catalyst (KOH) concentration (0.3%, 0.6%, 0.9%, 1.2%, and 1.5%). The efficiency of fatty acid methyl esters increased in response to lengthier reaction times, greater microwave power, higher methanol/oil mole ratio, and higher catalyst concentrations up to the optimal level. The optimal reaction conditions for microwave-assisted transesterification were 300 W microwave power, 1.2% catalyst concentration, a methanol/oil mole ratio of 1:2, and a reaction time of 4 min. Microwave-assisted transesterification was more effective than ohmic-, magnetic stirrer-, ultrasonic probe-, and ultrasonic bath-assisted transesterification methods. In conclusion, microwave-assisted transesterification can be suggested as a fast, efficient, and economical method compared to other transesterification methods.

H-Beta Zeolite as Catalyst for the Conversion of Carbohydrates into 5-Hydroxymethylfurfural: The Role of Calcination Temperature

H-Beta zeolite is a solid acid catalyst commonly utilized in the catalytic conversion of biomass resources. In this study, H-Beta zeolite was calcined at different temperatures (350, 550, 750, and 1000 °C) to explore the effects of high temperature-induced dealumination on its physicochemical properties and its catalytic ability to convert glucose into 5-hydroxymethylfurfural (HMF). It was shown that as the calcination temperature increased, the Si-O-Al bond of H-Beta zeolite was broken and its dealumination effect was enhanced. Dealumination led to the collapse of the framework of H-Beta zeolite and a reduction in the number of acid sites, which in turn reduced its catalytic performance and the efficiency of HMF formation from glucose. Furthermore, H-Beta zeolite exhibited an extraordinary catalytic ability for the production of HMF from carbohydrates. Using glucose and cellulose as substrates, superior HMF yields of 91% and 46%, respectively, were achieved under optimal reaction conditions. Further, calcination removes carbon deposits in the recovered H-Beta zeolite, but it affects the cycling stability of the catalyst. Meanwhile, the by-products formed during the synthesis of HMF from glucose catalyzed by H-Beta zeolite catalyst were also clearly detected.

Construction of DBU‐Based Poly(ionic liquid)s for the Conversion of CO2, Glycerol, and Propylene Oxide into Glycerol Carbonate

The development of efficient heterogeneous catalysts for upgrading CO2, a greenhouse gas, and glycerol (Gly), an untapped biomass resource, into glycerol carbonate (GC) remains a challenge. Herein, 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU)‐based poly(ionic liquid)s (PILs) were constructed for the one‐pot synthesis of GC from CO2, Gly, and propylene oxide. Among them, P‐DVB‐DBUVBI‐1 exhibited the best catalytic performance, achieving a GC yield of 90% under optimal reaction conditions (100 °C, 6 h). The PIL catalyst was easily recovered and reused, as demonstrated by stable activity over five cycles. Density functional theory calculations showed that owing the strong positive charge delocalization ability of DBU onium, DBU‐based PILs exhibit high nucleophilicity, which is the key to their efficient catalytic performance in the one‐pot reaction.

Green synthesis of silver nanoparticles using mature-pseudostem extracts of Alpinia nigra and their bioactivities

Abstract Green synthesis of silver nanoparticles (AgNPs) employing agricultural wastes as plant extracts to improve environmental benignity and also economic value added is the highlight of this research. The mature pseudostem of Alpinia nigra is an unbeneficial raw material discarded from several food ingredients and medicinal formulas. Therefore, this research focused on condition optimization for AgNP synthesis with ecofriendly techniques using A. nigra mature-pseudostem extracts and evaluation of their antioxidant, antibacterial activities, and toxicity with brine shrimp lethality assay (BSLA). The optimal reaction conditions were achieved by using 5 mM silver nitrate (AgNO3) solution with a volume ratio of 2:8 for the extract to AgNO3 at pH 12 under room temperature. The morphology and crystalline phase of the generated AgNPs were characterized using UV–visible spectrophotometry, field emission-scanning electron microscope (FE-SEM), energy dispersive X-ray, X-ray diffraction, and Fourier transform-infrared (FTIR) techniques. The FE-SEM analysis exposed spherical shapes with an average diameter of approximately 49 nm. The XRD analysis indicated their face center cubic structure, and the FTIR spectra confirmed that phytochemicals from A. nigra extract promoted the synthesis of AgNPs. In particular, the biosynthesized AgNPs presented potential antibacterial activity against both Staphylococcus aureus and Escherichia coli and effective antioxidant capacity using the DPPH radical scavenging assay. Additionally, non-toxic desired AgNPs were confirmed with BSLA.

Synthesis and characterization of perfluorocyclopentene‐thioether polymers

AbstractDue to their unique properties and use in high performance materials, the ability to obtain fluorinated polymers utilizing straightforward synthetic methods remains of interest. In this study, we report the facile synthesis of new fluoropolymers via nucleophilic addition of a di‐thiol to perfluorocyclopentene. Initially, model studies were completed with perfluorocyclopentene, benzenethiol and tetramethylsilane‐protected benzenethiol to identify the optimal reaction conditions for the polymerization. These reaction conditions were then utilized to prepare perfluorocyclopentene‐thioether polymers from perfluorocyclopentene and 4,4′‐thiobisbenzenethiol. The isolated polymers had molecular weight distributions consistent with step‐growth polymers and 19F NMR spectroscopy revealed that the addition of the nucleophile to perfluorocyclopentene was controlled. Analysis by DSC showed that the polymers were amorphous with glass transition temperatures around 65 °C. TGA in both air and nitrogen showed an initial degradation temperature around 370 °C, while the air analysis produced an additional plateau with a degradation temperature near 592 °C. This is the first known report of utilizing perfluorocyclopentene for the preparation of perfluorinated‐thioether polymers. © 2024 Society of Industrial Chemistry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

The treatment of petrochemical wastewater via ozone-persulfate coupled catalytic oxidation: mechanism of removal of soluble organic matter.

Petrochemical wastewater contains a variety of organic pollutants. Advanced oxidation processes (AOPs) are used for deep petrochemical wastewater treatment with distinct advantages, including the complete mineralization of organic substances, minimal residual byproducts, and compatibility with biological treatment systems. This work evaluates the effectiveness of three methods, namely, ozone, persulfate, and O3-PMS (ozone-persulfate) processes, which were compared to remove soluble organic matter. The O3-PMS process offered significant advantages in terms of organic matter removal efficiency. This process involves ozone dissolution in an aqueous persulfate solution, producing a more significant amount of hydroxyl radicals in comparison to single AOPs. The production of hydroxyl radicals and the synergistic effect of hydroxyl radicals and persulfate radicals were investigated. In the O3-PMS process, transition metal ions were added to understand the mechanism of the O3-PMS coupled catalytic oxidation system. The results showed that when the ozone concentration was in the range of 5 ~ 25mg/L, the dosage of persulfate was in the range of 0.01 ~ 0.05mol/L, the dosage of metal compounds was in the range of 0:0 ~ 2:1, and the reaction time was in the range of 0 ~ 2h; the optimum chemical oxygen demand (CODCr) and total organic content (TOC) removal effect was achieved under the coupled system with an ozone concentration of 10mg/L, a persulfate dosage of 0.02mol/L, a 1:2 dosage ratio of between Fe2+ and Cu2+ compounds, and a reaction time of 2h. Under optimal reaction conditions, the rates of CODCr and TOC removal reached 70% and 79.3%, respectively. Furthermore, the removal kinetics of the O3-PMS coupled catalytic oxidation system was analyzed to optimize the removal conditions of COD and TOC, and the mechanism regulating the degradation of dissolved organic matter was explored by three-dimensional fluorescence and GC-MS technology. Thus, O3-PMS coupled catalytic oxidation is an effective process for the deep treatment of wastewater. The careful selection of transition metal ions serves as a theoretical foundation for the subsequent preparation of catalysts for the ozone persulfate oxidation system, and this study provides a suitable reference for removing organic matter from petrochemical wastewater.

Simultaneous removal of perfluorooctanoic acid and thiocyanate by modified activated carbon fiber/persulfate system

In this study, NaOH-modified activated carbon fiber (NaOH-ACF) was used as a catalyst to activate persulfate (PS) for the removal of perfluorooctanoic acid (PFOA) and thiocyanate (SCN−) from wastewater. The effects of the crucial parameters in the NaOH-ACF/PS process, including NaOH-ACF dosage, PS concentration and initial pH, were investigated and optimized using response surface methodology. The experimental results indicated showed that under the optimal reaction conditions of NaOH-ACF dosage (0.40 g/L), PS concentration (2.0 mmol/L), pH (3.0), and temperature (25 °C), the removal efficiencies for PFOA and SCN− reached 93.63 % and 95.17 %, respectively, within 60 min of reaction. When PFOA and SCN− coexisted in the reaction system, it was observed that PFOA had minimal effect on the removal of SCN−, while SCN− actually enhanced the removal of PFOA. Free radical identification experiments demonstrated that the NaOH-ACF/PS system generated free radicals (O2−, SO4−, OH) and non-free radicals (1O2), which cooperatively facilitated the degradation of PFOA and SCN−. Furthermore, Liquid Chromatograph-Mass Spectrometer (LC-MS) analysis results have been used to speculate on the possible degradation pathways and intermediates of PFOA. The material characterization results indicated that NaOH-ACF possesses abundant surface functional groups with excellent adsorption and catalytic properties. Thus, the NaOH-ACF-activated PS advanced oxidation process offered a promising approach for the simultaneous removal of Perfluorinated compounds and thiocyanates.

Nickel(II)-Catalyzed Formal [3+2] Cycloadditions between Indoles and Donor-Acceptor Cyclopropanes.

This article describes the development of a nickel-catalyzed regio- and diastereoselective formal [3+2] cycloaddition between N-substituted indoles and donor-acceptor cyclopropanes to synthesize cyclopenta[b]indoles. Optimized reaction conditions provide the desired nitrogen-containing cycloadducts in up to 93% yield and dr 8.6:1 with complete regioselectivity. The substrate scope showed high tolerance to various substituted indoles and cyclopropanes, resulting in the synthesis of six new cyclopenta[b]indoles and the isolation of five derivatives previously reported in the literature. In addition, a mechanistic proposal for the reaction was studied through online reaction monitoring by ESI-MS, allowing for the identification of the reactive intermediates in the Ni(II) catalyzed process. X-ray crystallography confirmed the structure and relative endo stereochemistry of the products. This method enables the fast and efficient construction of fused indolines from readily accessible starting materials.

Kinetic Resolution of Cyclic Tertiary Alcohols with Lipase A from Candida antarctica

Enzyme‐catalyzed acylative kinetic resolution (KR) and dynamic kinetic resolution (DKR) of racemic primary and secondary alcohols have been widely reported to produce esters with high enantiomeric purity. In contrast, similar KRs of tertiary alcohols have been reported for only a limited range of substrates and require prolonged reaction times of several days. To gain deeper insight into the substrate scope and increase the process efficiency, we examined the reaction conditions using commercially available immobilized lipase A from Candida antarctica and found that the addition of the heterogeneous, inorganic base sodium carbonate significantly increased the reaction rate while maintaining high enantioselectivity. The use of vinyl hexanoate as the acyl donor provided esters that were stable during chromatography purification. The optimized reaction conditions were then successfully applied to a range of cyclic tertiary alcohols containing tetralin, dihydroindene, chromane, and thiochromane skeletons having, in part, a substituent on the aromatic ring. In this study on the structure–reactivity relationship of enzymatic KR‐type reactions, we achieved >30% conversion for various tertiary alcohols in 24 h at 25 °C, producing optically active esters with 88–99% ee.

Synthesis of Novel Trisubstituted Olefin-Type Probe Molecules Containing N-Heterocycles and Their Application in Detection of Malononitrile

Recently, the construction of the trisubstituted olefin-type probe molecules has elicited the attention of many researchers. However, the synthesis of the trisubstituted olefin-type probes containing two N-heterocycles simultaneously has been rarely reported. In this study, starting from the inexpensive mucobromic acid 1 and N-heterocyclic compound 2, we first utilized a simple one-step reaction to synthesize a series of trisubstituted olefin-type compounds 3 simultaneously bearing with the structure of two N-heterocyclic rings in the absence of transition metal catalysts with a yield of 62–86%. The optimal reaction conditions were systematically explored, and the structure of the obtained compounds 3 were well characterized with 1H NMR, 13C NMR, X-ray single-crystal and HR-MS. The preliminary observation showed that, in the presence of base, mucobromic acid 1 reacts as its ring-opening structure, and the successive nucleophilic substitution reaction and Michael addition reaction can generate the target product 3. Considering that the aldehyde group in the molecular structure of the trisubstituted olefin-type compounds 3 may react with malononitrile, we carried out some relevant investigations so as to realize the visual detection of malononitrile. Interestingly, among the products, compounds 3a–3c can be prepared in portable test strips through a simple process and used to achieve the naked-eye detection of malononitrile in environmental systems as designed.

Evaluation of the enantioselectivity of new chiral ligands based on imidazolidin-4-one derivatives.

The new chiral ligands I-III based on derivatives of imidazolidin-4-one were synthesised and characterised. The catalytic activity and enantioselectivity of their corresponding copper(II) complexes were studied in asymmetric Henry reactions. It was found that the enantioselectivity of these catalysts is overall very high and depends on the relative configuration of the ligand used; cis-configuration of ligand affords the nitroaldols with major enantiomer S- (up to 97% ee), whereas the application of ligands with trans-configuration led to nitroaldols with major R-enantiomer (up to 96% ee). The "proline-type" ligand IV was also tested in asymmetric aldol reactions. Under the optimised reaction conditions, aldol products with enantioselectivities of up to 91% ee were obtained.

Box-Behnken design-based isolation and chemical characterization of lignocellulosic fiber from Pueraria montana for weed management

The huge demand for natural fibers necessitates the search for non-traditional bioresources including invasive species which are deteriorating the ecosystem and biodiversity. The study aims to utilize Pueraria montana weed for the extraction of lignocellulosic fiber using both traditional (water retting) and chemical extraction methods to determine the better extraction method. Chemically extracted fiber showed 17.09 g/tex bundle strength whereas water-extracted fiber showed 11.7 g/tex bundle strength. Therefore, chemical extraction method was chosen for fiber isolation by optimization of reaction conditions using Box Behnken Design. Based on the design, optimal conditions obtained were 1 % w/v NaOH, 0.75 % v/v H2O2, and 3 days retting time. Solid-state NMR illustrated the breakdown of hemicellulose linkages at 25.89 ppm. FTIR revealed the disappearance of CO groups of hemicellulose at 1742 cm−1. TGA demonstrated thermal stability of chemically treated fiber up to 220 °C and activation energy of 60.122 KJ/mol. XRD evidenced that chemically extracted fiber has a crystallinity index of 71.1 % and a crystal size of 2 nm. Thus P. montana weed holds potential for the isolation of natural fiber as its chemical composition and properties are comparable to commercial lignocellulosic fibers. The study exemplifies the transformation of weed to a bioresource of natural fibers.

Iodine-catalyzed Synthesis, Antibacterial, and Antioxidant Activity of Isatin Derivatives

Isatin is a unique compound with many bioactivities such as antiviral, anti-HIV, antitumor, anti-inflammatory, anticonvulsant, and antifungal. In this study, isatin derivatives were synthesized with an iodine catalyst and tested for antibacterial and antioxidant activities. Isatin derivatives were conducted through a Knoevenagel condensation reaction between isatin and malononitrile. The products were confirmed by thin-layer chromatography, melting point apparatus, FTIR, UV-vis spectroscopy, and LC-MS. The optimum reaction conditions were obtained at 10% mol of catalyst, at boiling point ethanol solvent for 30 min. The yield of the isatin derivative products was 71% (3a), 61% (3b), and 67% (3c). The antibacterial activities of the synthesized compounds were weak activity against S. aureus and E. coli. The antioxidant activity test resulted in IC50 values of 266.47, 220.43, and 654.85 ppm for compounds 3a, 3b, and 3c, respectively. The synthesis method using an iodine catalyst in this reaction offers a higher product yield compared to a catalyst-free reaction.

Periodic open cellular structures (POCS) as catalyst support for intensified heat transport in the partial oxidation of methanol to formaldehyde

Heat transport in catalytic reactors is one of the most important factors in reactor design, especially for highly endo- or exothermic reactions. The limited thermal conductivity of randomly packed beds can be significantly improved when alternative catalyst supports are used. A new generation thereof are periodic open cellular structures (POCS), which are used in this study as catalyst support for the partial oxidation of methanol to formaldehyde, an exothermic gas phase reaction. A comparison to traditional packed bed reactors revealed that a POCS made of the highly conductive alloy AlSi10Mg can significantly reduce the hot-spot temperature, allowing almost isothermal operation at optimal reaction conditions. The improved temperature control allows for operation with higher methanol inlet concentrations and wall temperatures as compared to the commercial process. The beneficial heat transport properties of POCS were used to conduct isothermal kinetic measurements at elevated temperature. Based on these findings and the design freedom of additive manufacturing, an optimized cellular structure was designed and fabricated, which improved the heat transport especially in the critical inlet section of the reactor.