Organic Reactions Research Articles

Electrochemical hydrogenation and oxidation of organic species involving water.

Fossil fuel-driven thermochemical hydrogenation and oxidation using high-pressure H2 and O2 are still popular but energy-intensive CO2-emitting processes. At present, developing renewable energy-powered electrochemical technologies, especially those using clean, safe and easy-to-handle reducing agents and oxidants for organic hydrogenation and oxidation reactions, is urgently needed. Water is an ideal carrier of hydrogen and oxygen. Electrochemistry provides a powerful route to drive water splitting under ambient conditions. Thus, electrochemical hydrogenation and oxidation transformations involving water as the hydrogen source and oxidant, respectively, have been developed to be mild and efficient tools to synthesize organic hydrogenated and oxidized products. In this Review, we highlight the advances in water-participating electrochemical hydrogenation and oxidation reactions of representative organic molecules. Typical electrode materials, performance metrics and key characterization techniques are firstly introduced. General electrocatalyst design principles and controlling the microenvironment for promoting hydrogenation and oxygenation reactionsinvolving waterare summarized. Furthermore, paired hydrogenation and oxidation reactions are briefly introduced before finally discussing the challenges and future opportunities of this research field.

Recent Advances of CeO2-Based Composite Materials for Photocatalytic Applications.

Photocatalysis has the advantages of practical, sustainable and environmental protection, so it plays a significant role in energy transformation and environmental utilization. CeO2 has attracted widespread attention for its unique 4 f electrons, rich defect structures, high oxygen storage capacity and great chemical stability. In this paper, we review the structure of CeO2 and the common methods for the preparation of CeO2-based composites in the first part. In particular, we highlight the co-precipitation method, template method, and sol-gel method methods. Then, in the second part, we introduce the application of CeO2-based composites in photocatalysis, including photocatalytic CO2 reduction, hydrogen production, degradation, selective organic reaction, and photocatalytic nitrogen fixation. In addition, we discuss several modification techniques to improve the photocatalytic performance of CeO2-based composites, such as elemental doping, defect engineering, constructing heterojunction and morphology regulation. Finally, the challenges faced by CeO2-based composites are analyzed and their development prospects are prospected. This review provides a systematic summary of the recent advance of CeO2-based composites in the field of photocatalysis, which can provide useful references for the rational design of efficient CeO2-based composite photocatalysts for sustainable development.

Thermodynamic property estimations for aqueous primary, secondary, and tertiary alkylamines, benzylamines, and their corresponding aminiums across temperature and pressure are validated by measurements from experiments

On Earth and beyond, organic chemistry often occurs in the presence of water within environments that deviate drastically from ambient conditions (25 °C and 1 bar). Accurately predicting aqueous organic reaction pathways is crucial toward understanding planetary scale processes such as the cycling of elements crucial for life (e.g., carbon and nitrogen). Advanced thermodynamic modeling can be utilized to determine the favorability of various organic reactions based on geologically relevant ranges of temperature and pressure, as well as compositional variables (e.g., pH). However, data that would otherwise allow for a diversity of organic compounds and environmental conditions to be modeled are sparse and rarely tested with experiments, particularly with regard to organic-nitrogen compounds. In this work, we develop a framework to estimate thermodynamic properties at ambient conditions that can then be extrapolated across ranges of temperature and pressure for aqueous primary, secondary, and tertiary amines and aminiums (protonated amines), specifically those structures containing linear alkyl chains and benzyl functional groups. We also performed hydrothermal experiments (250 °C, ∼40 bar) involving reactions of methylamines to test our resulting thermodynamic models, and we compare our models for other alkylamines and benzylamines to previous empirical measurements from the literature. Specifically, we use existing thermodynamic data along with our estimates at ambient conditions in combination with a variety of existing extrapolation methods related to the revised Helgeson-Kirkham-Flowers (HKF) equations of state to generate temperature- and pressure-dependent predictions of acid dissociation constants (i.e., pKa values) that strongly agree with previous empirical measurements. We use similar methods to predict product distributions for reactions involving primary, secondary, and tertiary amines/aminiums, as well as ammonia/ammonium and corresponding alcohols whose collective distributions depend on reversible substitution reactions. Our predictions are in good agreement with our experimental results involving the methylamine reaction system as well as previous experiments involving the benzylamine reaction system, for which we also produced thermodynamic estimates involving benzyl alcohol. The agreement between independent theoretical predictions and experimental measurements suggests that our estimated properties can be applied to modeling amine chemistry in other experimental and natural aqueous systems that range in temperature and pressure, providing new tools for planetary exploration.

Facile Cu–MOF-derived Co3O4 mesoporous-structure as a cooperative catalyst for the reduction nitroarenes and dyes

The present study describes the environmentally friendly and cost-effective synthesis of magnetic, mesoporous structure-Co3O4 nanoparticles (m-Co3O4) utilizing almond peel as a biotemplate. This straightforward method yields a material with high surface area, as confirmed by various characterization techniques. Subsequently, the utilization of m-Co3O4, graphene oxide (GO), Cu(II)acetate (Cu), and asparagine enabled the successful synthesis of a novel magnetic MOF, namely GO–Cu–ASP–m-Co3O4 MOF. This catalyst revealed remarkable stability that could be easily recovered using a magnet for consecutive use without any significant decline in activity for eight cycles in nitro compound reduction and organic dye degradation reactions. Consequently, GO–Cu–ASP-m-Co3O4 MOF holds immense potential as a catalyst for reduction reactions, particularly in the production of valuable amines with high industrial value, as well as for the elimination of toxic-water pollutants such as organic dyes.

HISTORY OF DEVELOPMENTS IN GEOPOLYMER SCIENCE IN NEW ZEALAND: A BRIEF REVIEW

This brief review covers some of the highlights of the research into the chemistry and various applications of aluminosilicate geopolymers carried out in the Chemistry Department of Victoria University of Wellington over the last 20 years. Because these materials are generally amorphous to X-rays, the technique of Nuclear Magnetic Resonance with Magic Angle Spinning (MAS NMR) played a unique and important role in these studies. Many potential applications of geopolymers, were investigated over this period, including their use as structural materials, catalysts for commercially important organic reactions, bioactive materials and photoactive materials. Most of the initial work was carried out on clay-based starting materials because of their purity, but more practical materials were also developed, based on the by-products of industrial processing (fly ash, blast furnace slag, red mud, etc) This work led to more than 62 published papers in international journals, some of which are discussed here.

Backside versus Frontside SN2 Reactions of Alkyl Triflates and Alcohols.

Nucleophilic substitution reactions are elementary reactions in organic chemistry that are used in many synthetic routes. By quantum chemical methods, we have investigated the intrinsic competition between the backside SN2 (SN2-b) and frontside SN2 (SN2-f) pathways using a set of simple alkyl triflates as the electrophile in combination with a systematic series of phenols and partially fluorinated ethanol nucleophiles. It is revealed how and why the well-established mechanistic preference for the SN2-b pathway slowly erodes and can even be overruled by the unusual SN2-f substitution mechanism going from strong to weak alcohol nucleophiles. Activation strain analyses disclose that the SN2-b pathway is favored for strong alcohol nucleophiles because of the well-known intrinsically more efficient approach to the electrophile resulting in a more stabilizing nucleophile-electrophile interaction. In contrast, the preference of weaker alcohol nucleophiles shifts to the SN2-f pathway, benefiting from a stabilizing hydrogen bond interaction between the incoming alcohol and the leaving group. This hydrogen bond interaction is strengthened by the increased acidity of the weaker alcohol nucleophiles, thereby steering the mechanistic preference toward the frontside SN2 pathway.

3D-Printed Eosin Y-Based Heterogeneous Photocatalyst for Organic Reactions.

Heterogenization of Eosin Y by 3D-printing and its application in photocatalysis are reported. The approach allows a fine tuning of the photocatalyst morphology and its rapid preparation. Photocatalytic activity was evaluated through model organic reactions involving oxidation, reduction, and photosensitization pathways. The efficiency, recyclability and stability of 3D printed EY is remarkable paving the way to new generation of heterogeneous photocatalysts with a perfect control of their shape and adaptable to any photoreactors.

Gas Evolution as a Tool to Study Reaction Kinetics Under Biomimetic Conditions.

The field of bioorthogonal chemistry is rapidly growing, presenting successful applications of organic and transition metal-catalysed reactions in cells and living systems (in vivo). The development of such reactions typically proceeds through many iterative steps focused on biocompatibility and fast reaction kinetics to ensure product formation. However, obtaining kinetic data, even under simulated biological (biomimetic) conditions, remains a challenge due to substantial concentrations of salts and biomolecules hampering the use of typically employed solution-phase analytical techniques. In this study, we explored the suitability of gas evolution as a probe to study kinetics under biomimetic conditions. As proof of concept, we show that the progress of two transition metal-catalysed bioorthogonal chemical reactions can be accurately monitored, regardless of the complexity of the medium. As such, we introduce a protocol to gain more insight into the performance of a catalytic system under biomimetic conditions to further progress iterative catalyst development for in vivo applications.

Precise atom-to-atom mapping for organic reactions via human-in-the-loop machine learning

Atom-to-atom mapping (AAM) is a task of identifying the position of each atom in the molecules before and after a chemical reaction, which is important for understanding the reaction mechanism. As more machine learning (ML) models were developed for retrosynthesis and reaction outcome prediction recently, the quality of these models is highly dependent on the quality of the AAM in reaction datasets. Although there are algorithms using graph theory or unsupervised learning to label the AAM for reaction datasets, existing methods map the atoms based on substructure alignments instead of chemistry knowledge. Here, we present LocalMapper, an ML model that learns correct AAM from chemist-labeled reactions via human-in-the-loop machine learning. We show that LocalMapper can predict the AAM for 50 K reactions with 98.5% calibrated accuracy by learning from only 2% of the human-labeled reactions from the entire dataset. More importantly, the confident predictions given by LocalMapper, which cover 97% of 50 K reactions, show 100% accuracy for 3,000 randomly sampled reactions. In an out-of-distribution experiment, LocalMapper shows favorable performance over other existing methods. We expect LocalMapper can be used to generate more precise reaction AAM and improve the quality of future ML-based reaction prediction models.

Activation of iron oxide minerals in an aquifer by humic acid to promote adsorption of organic molecules

In aquifers, the sequestration and transformation of organic carbon are closely associated with soil iron oxides and can facilitate the release of iron ions from iron oxide minerals. There is a strong interaction between dissolved organic matter (DOM) and iron oxide minerals in aquifers, but the extent to which iron is activated by DOM exposure to active iron minerals in natural aquifers, the microscopic distribution of minerals on the surface, and the mechanisms involved in DOM molecular transformation are currently unclear. This study investigated the nonbiological reduction transformation and coupled adsorption of iron oxide minerals in aquifers containing DOM from both macro- and micro perspectives. The results of macroscopic dynamics experiments indicate that DOM can mediate soluble iron release during the reduction of iron oxide minerals, that pH strongly affects DOM removal, and that DOM is more efficiently degraded at low rather than high pH values, suggesting that a low pH is conducive to DOM adsorption and oxidation. Spherical aberration-corrected scanning transmission electron microscopy (SACTS) indicates that the reacted mineral surfaces are covered with large amounts of carbon and that dynamic agglomeration of iron, carbon, and oxygen occurs. At the nanoscale, three forms of DOM are found in the mineral surface agglomerates (on the surfaces, inside the surface agglomerates, and in the polymer pores). The microscopic organic carbon and iron mineral reaction patterns can form through oxidation reactions and selective adsorption effects. Fourier transform ion cyclotron resonance mass spectra indicate that both synergistic and antagonistic reactions occur between DOM and the minerals, that the release of iron is accompanied by DOM decomposition and humification, that large oxygen- and carbon-containing molecules are broken down into smaller oxygen- and carbon-containing compounds and that more molecules are produced through oxidation under acidic rather than alkaline conditions. These molecules provide adsorption sites for sediment, meaning that more iron can be released. Microscopic evidence for the release of iron was acquired. These results improve the understanding of the geochemical processes affecting iron in groundwater, the nonbiological transformation mechanisms that occur at the interfaces between natural iron minerals and organic matter, groundwater pollution control, and the environmental behavior of pollutants.

The Emerging Role of Polyethylene Glycol-Water (PEG-H2O) as the Benign Mixed Solvent System in Organic Synthesis

Abstract: Polyethylene glycol (PEG) has become a popular solvent and green catalyst for a variety of chemical reactions. It is a stable and biodegradable polymeric catalyst used in organic synthesis because it may be recycled numerous times without significantly losing its catalytic activity. Recently, the use of PEG-H2O mixed solvent systems in organic synthesis has gained popularity. This article presents an overview of PEG-H2O solvent system-mediated organic reactions, with a main focus on the importance of the solvent system. The study also focuses on recent developments in the PEG-H2O solvent system-mediated synthesis of a number of heterocy-clic compounds. Important characteristics of these PEG-H2O solvent systems include high atom economies, gentle reaction conditions, faster reaction rates, readily isolated side products and high yields. Results from various reactions showed that the choice of proper ratio of PEG: H2O solvent system plays a key role in product yields.

The aggregation behaviors of organic radicals in polar fluorinated arenes

AbstractPolar fluorinated arenes can promote organic free radical reactions, which have attracted scientists’ interest in recent years. However, it is still unknown how these solvents interact weakly with organic radical molecules to influence their reactivity. In this study, we investigated how organic free radicals aggregate in five polar fluorocarbon solvents, and demonstrated that different substituents can influence their aggregation behaviors. In these solvents, small organic radicals with simple substituents maintain a homogeneous solution; however, radicals with substituents that form intermolecular hydrogen bonds or with long‐chain aliphatic hydrocarbons tend to aggregate in them, whereas substituents of long‐chain aliphatic hydrocarbons tend to promote aggregation better. The critical aggregation concentrations of these aggregates are measured by concentration‐dependent UV–visible spectroscopy. Their topological morphologies are all spherical based on TEM. The compactness and rotational motivation speed of radical molecules within these aggregates are determined by EPR spectroscopy. The particle sizes of these aggregates are determined by analyzing their cyclic voltammograms. Most excitingly, electrochemical experiments reveal that the aggregation behaviors of free radical molecules with intermolecular hydrogen bonds can significantly increase their catalytic rate for electro‐oxidizing benzyl alcohol in such a solvent. The results of this study indicate that in polar fluorinated arenes organic radical molecules’ aggregation behaviors are related to their structures. This may provide guidelines for regulating organic radical reactivity in these solvents in the future.

Recyclable and Stable Porphyrin-Based Self-Assemblies by Electrostatic Force for Efficient Photocatalytic Organic Transformation.

Development of efficient, stable, and recyclable photocatalysts for organic synthesis is vital for transformation of traditional thermal organic chemistry into green sustainable organic chemistry. In this work, the study reports an electrostatic approach to assemble meso-tetra (4-sulfonate phenyl) porphyrin (TPPS)tetra (4-sulfonate phenyl) porphyrin (TPPS) as a donor and benzyl viologen (BV) as an acceptor into stable and recyclable photocatalyst for an efficient organic transformation reaction - aryl sulfide oxidation. By use of the electrostatic TPPS-BV photocatalysts, 0.1mmol aryl sulfide with electron-donating group can be completely transformed into aryl sulfoxide in 60min without overoxidation into sulfone, rendering near 100% yield and selectivity. The photocatalyst can be recycled up to 95% when 10mg amount is used. Mechanistic study reveals that efficient charge separation between TPPS and BV results in sufficient formation of superoxide which further reacts with the oxidized sulfide by the photocatalyst to produce the sulfoxide. This mechanistic pathway differs significantly from the previously proposed singlet oxygen-dominated process in homogeneous TPPS photocatalysis.

Double 1,2‐Carbon Migration at Mixed Heavier Sn=Ge Vinylidenes

Abstract1,2‐migration is one recurring isomerization reaction in organic chemistry. In contrast, double 1,2‐migration remains rare and limited to transition‐metal complexes. Herein, we describe the synthesis, characterization and reactivity of mixed heavier Sn=Ge vinylidenes. Double 1,2‐carbon migration enables the isomerization of the stannagermenylidene (3) to the germastannenylidene (4). X‐ray diffraction analysis and DFT calculations revealed that 3 and 4 feature a Sn=Ge double bond. The reaction of 3 with IMe4 (1,3,4,5‐tetramethylimidazoline‐2‐ylidene) results in the electron redistribution in the Sn=Ge core to give the germylone‐stannylene adduct (5). Moreover, treatment of 3 with 0.25 equiv. of (AlCp*)4 produces the heteronuclear aluminyl stannagermyne (6).

Double 1,2-Carbon Migration at Mixed Heavier Sn=Ge Vinylidenes.

1,2-migration is one recurring isomerization reaction in organic chemistry. In contrast, double 1,2-migration remains rare and limited to transition-metal complexes. Herein, we describe the synthesis, characterization and reactivity of mixed heavier Sn=Ge vinylidenes. Double 1,2-carbon migration enables the isomerization of the stannagermenylidene (3) to the germastannenylidene (4). X-ray diffraction analysis and DFT calculations revealed that 3 and 4 feature a Sn=Ge double bond. The reaction of 3 with IMe4 (1,3,4,5-tetramethylimidazoline-2-ylidene) results in the electron redistribution in the Sn=Ge core to give the germylone-stannylene adduct (5). Moreover, treatment of 3 with 0.25 equiv. of (AlCp*)4 produces the heteronuclear aluminyl stannagermyne (6).

Transition Metal and Photocatalyst Free Arylation via Photoexcitable Electron Donor Acceptor Complexes:Mediation and Catalysis

AbstractVisible‐light‐activated organic reactions unlock novel avenues for complex molecular transformations, impossible under standard “thermal” conditions, which makes them powerful tools in the arsenal of synthetic chemistry. However, transition metal‐based or organic photoredox catalysts are often used to ensure productive absorption of visible light, which might be not desirable to medicinal chemistry and industry due to toxicity, low sustainability, and high cost of most photocatalysts. A more environmentally and economically benign approach is based on the formation of transient electron donor‐acceptor (EDA) complexes between two reagents or a reagent and an additive, that readily absorb visible light, acting as internal photosensitizers. Within the EDA complex‐based arylation strategies, chemical transformations are mediated by noncovalent interaction between two molecules, namely between electron‐poor aryl halides or their synthetic equivalents and electron‐rich nucleophilic reagents or additives. Moreover, besides stoichiometric EDA complexes between two molecules, EDA complex based organocatalysis can be achieved in certain cases through regeneration of the donor molecules in the course of the reaction. Photoexcitation of the EDA complexes induces a single electron transfer (SET) process to generate aryl radical species for the arylation step. This Review will focus on the state‐of‐the‐art EDA complex‐based arylation strategies utilizing aryl halides, aryldiazonium, diaryliodonium, arylsulfonium and arylphosphonium salts as reactants, published mainly in the last five years.

An Overview of the Synthesis of Hexafluoroisopropanol and Its Key Intermediates

AbstractHexafluoroisopropanol (HFIP, 1,1,1,3,3,3-hexafluoro-2-propanol) is a fluorine-containing alcohol, which can be used in the preparation of fluorine-containing fine chemical, pharmaceutical, and pesticide ingredient. It is a widely used solvent in organic reactions that is miscible with water and many organic reagents. Hexafluoroacetone (HFA) is a key intermediate in the synthesis of HFIP. In this work, six methods for synthesizing HFA are discussed based on the different raw materials used. In addition, three methods of synthesizing HFIP, and the applications of HFIP are also reviewed.

Expression Analysis of Phenylpropanoid Pathway Genes and Phenylpropanoid Accumulation in Different Organs of Chelidonium majus L.

Objective This study set out to examine the phenylpropanoid pathway gene expression and phenolic compound accumulation in different organs of Chelidonium majus (C. majus). Methods Total RNA was extracted and expression of phenylpropanoid biosynthesis genes was assessed using quantitative real-time polymerase chain reaction in different organs of C. majus. In addition, the phenylpropanoid compounds were analyzed from different organs of C. majus by using high-performance liquid chromatography. Results The results demonstrate the variance in the expression levels of phenylpropanoid pathway genes in the flowers, leaves, stems, and roots of C. majus. CmPAL and CmC4H were expressed at their greatest levels in the stem, while CmCHS and CmCHI were strongly expressed in the leaf, and CmF3H, CmFLS, Cm4CL, and CmDFR were more abundant in the flower. The total phenolic contents in the different organs also varied significantly. The highest value was recorded in the flowers (2152.89 ± 78.71 μg/g dry wt.), which was 54.26 times higher than the lowest values obtained from roots (39.68 ± 0.05 μg/g dry wt.). Except for roots, rutin showed the highest level in all other organs. According to a heat map, the majority of the phenolic compounds were highest in the flower. By using variable importance in projection analysis, the most significant metabolite was found to be chlorogenic acid, which had a positive association with all phenolic chemicals, but it showed a negative correlation with trans-cinnamic acid. Except for trans-cinnamic acid, all other phenolic compounds likewise showed positive correlation with other phenolic compounds. Conclusions This work offers pertinent data on the expression analysis of genes involved in the phenylpropanoid biosynthetic pathway and the presence of phenolic compounds in C. majus. These findings will be helpful for the researcher to understand the relationship between the expression level of phenylpropanoid pathway genes and phenylpropanoid compound accumulation in C. majus.

Cover Picture: Organic Photoredox Reactions in Two‐Molecule Photoredox System (Chem. Rec. 3/2024)

Cover Picture: Organic Photoredox Reactions in Two‐Molecule Photoredox System (Chem. Rec. 3/2024)

Copper-Bisbenzimidazole Complexes as Biomimetic Catalysts in Organic Transformations

Abstract: Copper complexes have biological applications as well as catalytic importance in performing organic reactions. Besides finding utilities in metalloproteins, enzymes, or molecular magnetism, they have been used extensively as catalysts in the formation ofcarbon–carbon or carbon– heteroatom bonds, in addition to many other reactions. This has been achieved by the rational selection of the organic ligands with suitable coordination sites for attaining ideal geometries. The binding of one such organic ligand, bisbenzimidazole, with copper results in complexes with varied shapes, structures, and activities, enhancing their catalytic potential and hence useful applications. This review describes the catalytic applications of bisbenzimidazole based copper (II)/(I) complexes in various useful organic transformations. It also provides an in-depth knowledge of the mechanistic pathways of the transformations involving copper complexes and their multipurpose utility as catalysts, which may help in the development of improved copper catalysts for the future.