Reaction Conditions Research Articles

Necessary Stability Conditions for Reaction–Diffusion–ODE Systems

Necessary Stability Conditions for Reaction–Diffusion–ODE Systems

Recent Progress for the Synthesis of Pyrrole Derivatives – An Update

Abstract: Pyrrole is a versatile heterocyclic moiety exhibiting a wide range of pharmacological actions with high therapeutic value. The importance of pyrrole in the pharmaceutical field lies in its versatility, selectivity, and biocompatibility, and these properties make it a valuable tool for drug design and development. The pyrrole moiety is a fundamental building block for many biologically active molecules and has gathered significant attention in the fields of medicinal and organic chemistry; hence, its synthesis has been a crucial area for research. There are various conventional as well as modern approaches to acquiring a series of pyrrole scaffolds, with a wide range of attractive features and drawbacks pertaining to each approach. An extensive amount of literature must be studied to compare the best synthetic routes. This article highlights the applications of pyrrole derivatives in various fields, such as drug discovery, material science, and catalysis, and provides an overview of modern synthetic pathways that include metals, nanomaterials, and complex heterogeneous catalysed methods for pyrrole derivatives. Special emphasis is given to the use of green chemistry principles like green solvent-based methods, microwave-aided methods, and solvent-free methods in the synthesis of pyrroles, with the recent developments and prospects in the synthetic and organic chemistry fields. Overall, this review article provides a comprehensive overview of the synthesis of pyrroles and complies with all the possible developments in the synthetic routes for pyrroles within 2015– 2022. Among all, the reactions catalysed by proline, copper oxides, and oxones have been shown to be the most effective synthetic route for pyrrole derivatives at mild reaction conditions and with excellent yields. This information will be helpful for researchers interested in the development of new pyrrole-based compounds. The categorization in this review provides an easy means for the reader to rationally select the best possible synthetic method for pyrrole derivatives.

EMIM] [OAc]: An Efficient Ionic Liquid Medium for the Synthesis of New 4-(furan/pyrrole/thiophene-2-yl)-3, 4-dihydro-1H-chromeno [4,3-d] pyrimidine-2,5-diones and Molecular Docking Studies

Abstract: An efficient synthesis of Chromeno[b]pyrimidine derivatives 4 has been achieved by treating 4-hydroxy-2H-chromen-2-one 1, furan-2-carbaldehyde / 1H-pyrrole-2-carbaldehyde/ thiophene-2- carbaldehyde 2, and urea/thiourea 3 at 65-70 °C for 90-120 min using 1-Ethyl-3-methylimidazolium acetate as ionic liquid and medium with good yields 86-90%. This synthetic method has numerous advantages, including high yields, a simple protocol, environmental friendliness, brief reaction times, and mild reaction conditions. Using a catalytically active ionic liquid as the medium eliminates the need for a catalyst and a solvent. In this study, the docking score of the synthesized compounds was found to be between -8 to -9 kcal/mol similar to the co-crystal. Additionally, the compounds maintained their amino acid interactions with Tyr 281 (coagulation protein; 6WV3) and Thr 179 (tubulin polymerization protein; 5LYJ.pdb).

An improved synthesis of alkyl AMP esters

Enzymes belonging to the Acyl-CoA/NRPS/Luciferase (ANL) superfamily of enzymes, are significant targets in drug development. One member of this superfamily is Acetyl-CoA Synthetase (ACS). This enzyme is an emerging target for the treatment of various infectious diseases and cancer. Alkyl AMP esters have emerged as potent inhibitors of ACS. Previous methods for synthesizing these esters often involved water-based reactions or necessitate purification through reverse phase prep-HPLC or ion-exchange chromatography. To address these challenges, we developed a new approach utilizing 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl) to couple 5′-adenylic acid to the corresponding alcohol, utilizing triethylamine as the base. This method yielded primary, secondary, unsaturated, and cyclic alcohols in excellent yields. Importantly, we optimized the reaction conditions to achieve excellent yield and purity without the need for reverse phase prep-HPLC or ion exchange chromatography. Instead, purification was achieved through silica gel chromatography using Biotage ® Sfar spherical silica gel.

Regeneration of bulk and silica-supported gallium oxide catalysts applied in the dehydrogenation of methanol to formaldehyde and hydrogen by reaction-oxygen regeneration cycles and oxygen pulses in the feed

The oxygen-free dehydrogenation of methanol to formaldehyde and hydrogen is a potential alternative to the established industrial oxidative dehydrogenation yielding aqueous formaldehyde solutions. Advantages are the production of anhydrous formaldehyde and of hydrogen as a valuable coupled product. However, fast deactivation of the catalyst occurs under the high-temperature reaction conditions mainly due to coking, which can be overcome by applying oxygen at a temperature high enough to allow fast oxidation of the carbon deposits but low enough to prevent the loss of Ga. From an engineering point of view, a stable reaction temperature in the catalyst bed and a high H2 yield have to be maintained, requiring that the catalyst enables methanol dehydrogenation, but not the oxidation of hydrogen to water. Thus, two modes of regeneration of GaOx-based catalysts were investigated using reaction − oxygen regeneration cycles and oxygen pulses in the feed. When using bulk Ga2O3 as catalyst and applying optimized reaction-regeneration cycles, a formaldehyde yield of 51 % and a hydrogen yield of 45 % at a stable methanol conversion of 65 % were achieved, whereas undiluted O2 pulsed into the feed every 30 s resulted in a continuous formaldehyde yield of 40 % and a hydrogen yield of 35 % at a stable methanol conversion of 59 % with water yields below 2 % and 4 %, respectively. The effects of the two operation modes on stability and product distribution are discussed in terms of the carbon removal rate from the surface, refilling of oxygen vacancies and parasitic reactions in the presence of oxygen. Specifically, the consumption of O2 did not lead to excessive water formation but preferentially effected the oxidation of the carbon deposits to CO and CO2.

Enhanced catalytic performance of ethyl-levulinate to γ-valerolactone: Effect of copper loading on Ni/KIT-5 catalyst

A facile wet impregnation method was employed to prepare a bimetallic Ni–Cu catalyst on a mesoporous KIT-5 support, keeping the nickel loading constant (5 wt%) while varying the copper wt.% (xCu, where x = 8, 10, 12, 14). Several physico-chemical techniques, including X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), temperature-programmed desorption of ammonia (NH3-TPD), temperature-programmed reduction of hydrogen (H2-TPR), and X-ray photoelectron spectroscopy (XPS), were utilized for catalyst characterization. An environmentally friendly NiCu bimetallic-supported catalyst system was developed in response to many problems, including metal leaching, sintering, and cost. A mesoporous KIT-5 silica support with a large surface area was used. The hydrogenation of ethyl levulinate to gamma-valerolactone was studied utilizing a high-pressure stirred reactor and a range of reaction temperatures (120–160 °C), hydrogen pressures (10–30 bar), and reaction periods. Various catalysts were used in the investigation. Among all tested catalysts, the 12Cu–5Ni/KIT-5 one shows excellent activity. The best GVL yield is 84% at a conversion of 100% after 8 h of treatment at 150 °C and 25 bar H2 pressure; the promotion is also 76.1%. Optimization of reaction conditions was shown to correlate the physicochemical parameters of the catalyst with its activity.

Single nickel atoms anchored on porous N-doped nanocarbon with dual reaction sites for highly-efficient transfer hydrogenation of furfural to furfuryl alcohol

The non-precious metal single-atom catalysts (SACs) supported on carbon materials for the catalytic transfer hydrogenation (CTH) of α,β-unsaturated aldehydes (UAL) still suffer from the problems of harsh reaction conditions and low activity. In this work, nickel SACs anchored on porous N-doped nanocarbon (Ni1/NC900) with dual reaction sites were synthesized using the high internal-phase emulsion (HIPE) template method combined with impregnation. The Ni1/NC900 catalyst exhibited remarkable catalytic activity for the CTH of furfural (FF) to furfuryl alcohol (FFA), achieving >99.0 % conversion and selectivity at 100 °C for 60 min, with a turnover frequency (TOF) of 2908.1 h−1, surpassing other reported nickel-based catalysts by 1–3 orders of magnitude. The excellent catalytic performance of Ni1/NC900 was attributed to the high mass transfer efficiency (HMTE) of the support and the dual reaction sites of Ni–N4 and pyridinic N, where Ni–N4 as Lewis acidic site for adsorption of FF and isopropanol (i-PrOH), while the adjacent pyridinic N as Lewis basic site for the deprotonation of i-PrOH. The isotope labeling experiments revealed that the hydrogenation of FF was accomplished by proton transfer with i-PrOH, in agreement with the intermolecular hydride transfer mechanism. Furthermore, Ni1/NC900 demonstrated excellent stability and well general applicability, demonstrating its potential for industrial applications. This work provides a reference for the application of carbon-based non-precious metal SACs in the CTH reaction of UAL.

Improving Photocatalytic Efficiency with Titanium Dioxide Quantum Dots

Titanium dioxide quantum dots (TiO2-QDs), synthesized using a microwave-assisted method, represent a significant advancement in photocatalysis, particularly in the treatment of environmental pollutants. This study focuses on TiO2-QDs synthesized at 200°C for a duration of 5 minutes, using titanium butoxide as a precursor. Characterization through TEM, XRD, PL, and UV-Vis-DRS analyses revealed uniform quantum dots with an average size of 5.28 nm, a bandgap energy of 3.22 eV, and a crystalline anatase phase, indicative of high photocatalytic activity. Notably, these TiO2-QDs demonstrated exceptional performance in degrading methylene blue (MB) in water, achieving a remarkable treatment efficiency of 97.6% in 120 min, significantly outperforming both conventional titanium dioxide nanoparticles and commercial titanium dioxide materials. The reaction conditions were evaluated based on factors such as catalyst dose, initial MB concentration, and pH. The results indicate that optimal degradation efficiency of MB was achieved at a pH of 7, with a catalyst dose of 0.15 g/L and at a low MB concentration. The efficiency slightly decreased to 94.5% after five reuse cycles, emphasizing its significant reusability and stability. Copyright © 2024 by Authors, Published by BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Machine learning-guided prediction of hydroformylation.

A holistic model for predicting yield and linear selectivity for the hydroformylation of 1-octene was developed by machine learning using the experimental data collected from literatures. Physical organic chemistry (POC) parameter-based descriptors were adopted to represent pre-catalyst molecular features. Machine learning models trained respectively by Random Forests (RF) and Extreme Gradient Boost (XGBoost) algorithm showed remarkable performance on predicting linear selectivity. The method can also comprehensively map the correlation between reaction conditions and the results. The accuracy of the prediction results was verified by experimental data.

Colloidal Bimetallic RuNi Particles and their Behaviour in Catalytic Quinoline Hydrogenation.

Colloidal metal nanoparticles exhibit interesting catalytic properties for the hydrogenation of (hetero)arenes. Catalysts based on precious metals, such as Ru and Rh, promote this reaction efficiently under mild reaction conditions. In contrast, heterogeneous catalysts based on earth-abundant metals can selectively hydrogenate (hetero)arenes but require harsher reaction conditions. Bimetallic catalysts that combine precious and earth-abundant metals are interesting materials to mitigate the drawbacks of each component. To this end, RuNi nanoparticles bearing a phosphine ligand were prepared through the decomposition of [Ru(η4-C8H12)(η6-C8H10)] and [Ni(η4-C8H12)2] by H2 at 85 °C. Wide angle X-ray scattering confirmed a bimetallic segregated structure, with Ni predominantly on the surface. Spectroscopic analyses revealed that the phosphine ligand coordinated to the surface of both metals, suggesting, as well, a partial Ni shell covering the Ru core. The RuNi-based nanomaterials were used as catalysts in the hydrogenation of quinoline to assess the impact of the metallic composition and of the stabilizing agent on their catalytic performance.

Next‐Generation Time‐Resolved Electron Paramagnetic Resonance for Direct Visualizing Mechanisms in Radical Chemistry

AbstractRadical chemistry is an important research field that plays a vital role in life science, material science, and energy conversions. However, directly visualizing the transient open‐shell intermediates unambiguously in radical chemistry is a significant and long‐standing challenge. Recently, we have developed an innovative ultrawide single‐sideband phase‐sensitive detection (U‐PSD) time‐resolved electron paramagnetic resonance (TREPR) technique, which enables the characterization of diverse transient radical intermediates and mechanistic studies close to reaction conditions. In this brief review, we will offer an outline of the principles underlying our U‐PSD TREPR technique, and present examples highlighting the technique's ability to accurately characterize and track free radical intermediates in photocatalytic reactions.

Solvent‐Free Dehydrogenative C−H Chalcogenations of Pyrazolones Using Mechanochemistry

AbstractA mechanochemical cross‐dehydrogenative coupling reaction of pyrazolones with thiols using ball milling is described. Benzeneselenol and dichalcogenide substrates are also compatible under mild reaction conditions, yielding up to 99 %. Notable features of this reaction include its metal‐ and solvent‐free, wide substrate scope and good functional group tolerance. Preliminary mechanistic investigations suggest that a radical pathway is likely involved in this C−H chalcogenation reaction.

Oxidative cleavage of C–S bonds in 2,2-disubstituted 1,3- dithiolanes and 1,3- oxathiolanes with singlet molecular oxygen generated from trans-5-hydroperoxy-3,5 dimethyl-1,2-dioxolan-3-yl ethaneperoxate

A new protocol for the synthetically useful deprotection of 1,3-dithiolane and 1,3-oxathiolane protected moieties has been developed. A series of 2,2-disubstituted 1,3 – dithiolanes and 1,3 – oxathiolanes was effectively deprotected to release the corresponding carbonyl compounds. The combination of trans-5-hydroperoxy-3,5-dimethyl-1,2-dioxolan-3-yl-ethaneperoxate and KOH was shown to be an effective system for the oxidative cleavage of C–S bonds under mild reaction conditions at room temperature. The active oxidizing specie is singlet molecular oxygen. It is generated via fragmentation of the trans-5-hydroperoxy-3,5-dimethyl-1,2 – dioxolane-3-yl ethaneperoxate with the help of KOH.

Construction of magnetic FeP/CdS composites as photo‐Fenton‐like catalysts to realize high‐efficiency degradation of tetracycline hydrochloride

Photocatalysis is an efficient technology for the degradation of pollutants. However, it still needs to be improved. In this study, magnetic Z‐scheme FeP/CdS composites heterojunction photocatalysts were prepared by a facile hydrothermal method, and the structure, morphology, optical and photocatalytic properties of the prepared composites were investigated in detail. The efficiency of tetracycline hydrochloride (TCH) removal by FeP/CdS composites was investigated under different reaction conditions (including different FeP and CdS ratios, catalyst dosage, hydrogen peroxide consumption, temperature, and initial pH). FeP/CdS composites exhibited better catalytic performance compared with pure components. The F1Cd1 composite (mass ratio of FeP to CdS is 1:1) achieved 92.7% removal efficiency of TCH, moreover, the F1Cd1 composite still exhibits a high stability after five consecutive cycles. The capture experiments on the active material showed that the removal of TCH by the F1Cd1 composite was mainly dominated by •OH; however, •O2−, e‐, and h+ played a minor role, and the degradation mechanism was revealed by combining various characterization techniques. The introduction of cadmium sulfide formed an effective photogenerated carrier transport channel at the interface with the iron phosphide surface, which could accelerate the transfer and separation of photo‐excited e‐/h+ pairs, thus improving the degradation performance of TCH.

Dimethyl Sulfoxide Promoted Quinazolinone Synthesis

AbstractAn efficient and one‐step synthesis of quinazolinones using 2‐aminobenzamide and benzylamine in DMSO under external catalyst‐ and base‐free conditions is reported. A broad substrate scope and environment‐benign mild reaction conditions are the major attributes of this straightforward synthesis. Moreover, the synthesized quinazolinone derivatives were used to produce pharmaceutically active rutaecarpine analogues using a two‐step reaction: N‐alkylation followed by intramolecular cyclization.

Copper-Catalyzed γ-C(sp3)-H Lactamization and Iminolactonization.

Despite extensive efforts to develop γ-lactamization reactions for pyrrolidinone synthesis using either cyclometallation, C-H insertion, or radical C-H abstraction strategies, γ-lactamization reactions of aliphatic amides using practical catalysts and common protecting groups remain extremely rare. Herein we report copper-catalyzed γ-C(sp3)-H lactamization and iminolactonization of tosyl-protected aliphatic amides using inexpensive Selectfluor as the sole oxidant. A switchable selectivity of γ-Lactams or γ-iminolactones can be obtained by using two different sets of reaction conditions. Notably, structurally diverse spiro-, fused-, and bridged-lactams and iminolactones, as well as isoindolinones are accessible by this method. Further derivatization of the γ-lactam products enables the synthesis of a range of biologically important motifs, including γ-amino acids, δ-amino alcohols, and pyrrolidines.

Copper‐Catalyzed γ‐C(sp3)−H Lactamization and Iminolactonization

Despite extensive efforts to develop γ‐lactamization reactions for pyrrolidinone synthesis using either cyclometallation, C−H insertion, or radical C−H abstraction strategies, γ‐lactamization reactions of aliphatic amides using practical catalysts and common protecting groups remain extremely rare. Herein we report copper‐catalyzed γ‐C(sp3)−H lactamization and iminolactonization of tosyl‐protected aliphatic amides using inexpensive Selectfluor as the sole oxidant. A switchable selectivity of γ‐Lactams or γ‐iminolactones can be obtained by using two different sets of reaction conditions. Notably, structurally diverse spiro‐, fused‐, and bridged‐lactams and iminolactones, as well as isoindolinones are accessible by this method. Further derivatization of the γ‐lactam products enables the synthesis of a range of biologically important motifs, including γ‐amino acids, δ‐amino alcohols, and pyrrolidines.

A Facile and Regioselective Synthesis of 2‐Formamidothiazoles via the C−H Formamidation of Thiazole N‐oxides with Isocyanides

A facile, microwave‐promoted, regioselective C−H formamidation of thiazole N‐oxides with isocyanides in the presence of TBDPSCl was developed. Various 2‐(N‐substituted formamido)thiazoles were obtained in moderate to high yields. In the case of the C2‐substituted thiazole N‐oxides, the C‐H formamidation took place selectively at the C4 position of the thiazole ring. This transformation is also applicable to some other N‐containing heterocyclic derivatives such as pyridine, quinoline, and pyridazine N‐oxides and has advantages such as broad substrate tolerance, high regioselectivity, and mild reaction conditions.

Microwave-Assisted Conversion of 5-Hydroxymethylfurfural into 2,5-Furandicarboxylic Acid over CuCo Oxide.

A series of CuCo bimetallic catalysts were prepared via the co-precipitation method for the catalytic transformation of biomass-derived 5-hydroxymethylfurfural (HMF) into 2,5-furandicarboxylic acid (FDCA). FDCA acts as a precursor for biodegradable biopolymer polyethylene furanoate production, thereby achieving a carbon-neutral approach. Out of all the synthesized catalysts, CuCo(1:1) showed remarkable catalytic activity and yielded 70.67% FDCA while achieving 100% HMF conversion in 5 minutes at 50 ℃ temperature in the presence of tert-butyl hydroperoxide as an oxidant. Synergistic effects of the catalyst, such as adsorbed oxygen, relative oxygen vacancy, lesser pore size, and pore volume, were key factors attributed to the catalyst's excellent activity. The synthesized catalyst showed good recyclability with a minimal decrease in FDCA yield up to 5 cycles. Pre and post-characterization of catalysts such as BET, TEM, FE-SEM, XRD, H2-TPR, CO2 TPD, ICP-OES, and XPS were done to correlate the catalyst's properties with its activity. In addition, the effect of reaction parameters such as stirring speed, temperature reaction time, catalyst weight, base, and oxidant was studied to achieve optimum reaction conditions. The reaction products were analyzed quantitatively and qualitatively using HPLC and HR-MS.

Synthesis of Diketopyrrolopyrrole Based Photoactive Materials via Photoredox C−H Activation

AbstractThe synthesis of diketopyrrolopyrrole (DPP) derivatives followed the well‐known conventional cross‐coupling methods such as Suzuki, Stille, Sonogashira, and Negishi cross‐coupling reactions. However, these methods required unfavorable reaction conditions, organometallic precursors, and high temperatures. In addition, the synthesis of conventional cross‐coupling partners including organoboranes, stannane, and acetylenes required drastic reaction conditions and strong bases. In this work, a wide variety of thiophene‐diketopyrrolopyrrole (TDPP)‐based semiconducting materials (36 compounds) were synthesized via Pd‐catalysed photoredox methodology by using N‐hydroxyphthalimide (NHP) based coupling partners, which can be readily prepared from N‐hydroxyphthalimide and carboxylic acid or aldehyde derivatives via single step C−O bond formation reactions with good yield (80–90 %). This methodology minimizes additional synthetic steps, harsh reaction conditions, and high temperature (100–150 °C). Optoelectronic studies suggest that the synthesized materials have suitable band gap, HOMO and LUMO levels for variety of optoelectronic applications. To the best of our knowledge, this is the first report on the synthesis of TDPP‐based π‐conjugated materials via the photoredox method.