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Reactions, Volume 7, Issue 1 (March 2026) – 18 articles

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21 pages, 1842 KB  
Article
Obtaining Biodiesel from Soybean Vegetable Oil Using a Hydrodynamic Cavitation Reactor
by Luz Clara Andia-Marron, Jessica Abad-Salcca, Juan Taumaturgo Medina-Collana, Edgar Williams Villanueva-Martinez, Jorge Amador López-Herrera, Richard Brandon Guevara-Salcedo, Leonard Ordoñez-Santa Maria, Rodolfo Paz-Salazar, Fredy Andrés Taipe-Castro, Jorge Alberto Montaño-Pisfil and Segundo Alberto Vásquez-Llanos
Reactions 2026, 7(1), 18; https://doi.org/10.3390/reactions7010018 - 6 Mar 2026
Abstract
Hydrodynamic cavitation (HC) is an efficient technique for biodiesel production. The main contribution of this study is the development of a modular reactor with a universal stainless steel joint, whose design facilitates the installation, replacement, and maintenance of the orifice plate by eliminating [...] Read more.
Hydrodynamic cavitation (HC) is an efficient technique for biodiesel production. The main contribution of this study is the development of a modular reactor with a universal stainless steel joint, whose design facilitates the installation, replacement, and maintenance of the orifice plate by eliminating flanges and bolts during assembly. Using this reactor, the study evaluated the synergistic interaction between feed pressure and methanol:oil molar ratio in the transesterification of soybean oil, employing a 32 factorial design. The orifice plate was 3 mm thick and had 19 holes with a diameter of 1.0 mm, installed downstream of the pump. The process was carried out for 45 min, using NaOH at 1 wt% relative to the oil and at 60 ± 5 °C. Feed pressures of 1.72, 2.41, and 3.10 bar and methanol:oil molar ratios of 6:1, 8:1, and 10:1 were evaluated, reaching a maximum yield of 92.98% at 3.10 bar and 8:1. Analysis of variance (ANOVA) confirmed a significant interaction (p < 0.0001) and allowed a second-order polynomial model to be fitted (R2 = 0.9981). In contrast, conventional mechanical agitation required 90 min to achieve 95% yield. The biodiesel produced met most American Society for Testing and Materials (ASTM) D6751 requirements, confirming the potential of HC as a viable alternative for intensifying biodiesel production. Full article
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10 pages, 755 KB  
Article
Influence of Ethanol Content on the Electrooxidation of Triethanolamine in Highly Apolar Media on Platinum Microelectrode
by László Kiss, Heng Li, Xiao-Hang Chen and Sándor Kunsági-Máté
Reactions 2026, 7(1), 17; https://doi.org/10.3390/reactions7010017 - 2 Mar 2026
Viewed by 109
Abstract
Ethanol is widely used as an additive in fuels, so its effect on the electrochemical oxidation of triethanolamine was investigated on a 25 μm platinum microelectrode. Ethyl acetate was applied as a cosolvent to increase the permittivity of the medium. A hydrocarbon n [...] Read more.
Ethanol is widely used as an additive in fuels, so its effect on the electrochemical oxidation of triethanolamine was investigated on a 25 μm platinum microelectrode. Ethyl acetate was applied as a cosolvent to increase the permittivity of the medium. A hydrocarbon n-heptane, typically present in gasohol samples as the main component, was studied, and its solutions prepared with ethanol in the entire concentration range (between 0 and 100 v/v% ethanol contents) were mixed with ethyl acetate. The as-prepared liquid mixtures were prepared separately, and they were mixed with ethyl acetate in uniform ratios. Triethanolamine, the selected redox-active compound, exhibited a sharp peak in ethyl acetate at the 15 mM concentration. The changes in the voltammograms served as a good template for quantitative analysis of ethanol content. The most suitable analytical signal used for it was the current minimum after the anodic peak, and this parameter proved more sensitive and reproducible than the anodic peak height itself. The scatterings of the current minimum values were typically within some nanoamperes. MTBE (methyl tert-butyl ether) was added to the apolar mixtures of ethanol, and this ether had a negligible interfering effect on the estimation of ethanol content. Full article
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20 pages, 5052 KB  
Article
Polyaniline-Pyrrole as a Potential Cathode Modifier in Magnesium-Sulfur Battery: An Ab Initio Study
by Hassan Shoyiga and Msimelelo Siswana
Reactions 2026, 7(1), 16; https://doi.org/10.3390/reactions7010016 - 23 Feb 2026
Viewed by 267
Abstract
Magnesium-sulfur (Mg-S) batteries present a compelling energy storage solution, characterised by their remarkable theoretical energy density and economic viability. Nonetheless, challenges arise, including swift capacity degradation and suboptimal polysulfide (acting as an electronic and ionic insulator) utilisation, mainly due to a phenomenon known [...] Read more.
Magnesium-sulfur (Mg-S) batteries present a compelling energy storage solution, characterised by their remarkable theoretical energy density and economic viability. Nonetheless, challenges arise, including swift capacity degradation and suboptimal polysulfide (acting as an electronic and ionic insulator) utilisation, mainly due to a phenomenon known as the polysulfide “shuttle effect.” This effect also leads to a decline in battery performance. The Becke, 3-parameter, Lee-Yang-Parr (B3LYP) functional and 6-311G (d,p) basis set were used to examine the optoelectronic and charge-transfer properties of a polyaniline-pyrrole (PANIPyr) composite, emphasising interatomic and electronic interactions that enhance charge transport and oxidation of MgS2. The findings demonstrate the presence of coordination bonding between hydrogen in pyrrole and the N ion in quinonediimine of polyaniline, significantly enhancing the electrical properties of PANI. The PANIPyr_P1 (P1-pyrrole attached at position one) configuration exhibits the lowest Ɛgap and the highest charge-transfer capacity, compared to other studied molecules in this work, thereby improving reactivity towards polysulfides in comparison to pure PANI. Significant electrical interactions at this site establish accessible electrophilic and nucleophilic regions that stabilise the ionic sides of the polysulfides, thus reducing the shuttle effect and improving charge transport at the interface. PANIPyr_P1 demonstrates viability for minimising polysulfide migration and enhancing cathodic efficiency in Mg-S batteries, thereby laying a foundation for future investigations into polymer-based cathode modifiers. Full article
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17 pages, 21322 KB  
Article
Effect of the Dopant and Carbonaceous Support of the Perovskite Type LaNi0.9X0.1O3 (X = Fe, Mn or Pd) on the Performance of Zn–Air Battery
by Karlo I. Martinez-Soto, Mara Beltrán-Gastélum, Noé Arjona, Sergio Pérez-Sicairos, Samgopiraj Velraj, Jiahong Zhu and Moises I. Salazar-Gastélum
Reactions 2026, 7(1), 15; https://doi.org/10.3390/reactions7010015 - 18 Feb 2026
Viewed by 281
Abstract
The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are two processes that occur during the operation of the cathodic electrode in Zn–Air batteries, which enable the integration of alternative energy sources into electrical energy distribution systems. Transition metal oxides, such as [...] Read more.
The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are two processes that occur during the operation of the cathodic electrode in Zn–Air batteries, which enable the integration of alternative energy sources into electrical energy distribution systems. Transition metal oxides, such as perovskites based on LaNiO3, are promising electrocatalysts for the ORR and OER in alkaline medium due to their versatile structure, allowing for the substitution of certain atoms with dopants, which enhances the catalytic activity for both reactions. This work reports an electrochemical study of the catalytic activity toward ORR and OER of perovskite catalysts (LaNiO3 doped with transition metals (Fe, Mn, or Pd)) in the presence of carbon-based materials as supports (multiwalled carbon nanotubes (MWCNT), graphene oxide nanosheets (GO), and graphitic carbon (C)). The results revealed interesting catalytic properties in both reactions, particularly La(Ni0.9Pd0.1)O3/MWCNT, which showed an ORR activation potential of 0.87 V vs. RHE, comparable to that of the commercial Pt/C catalyst (0.99 V vs. RHE), while the overpotential for OER was lower than that of the Pt/C catalyst (1.68 V vs. RHE for La(Ni0.9Pd0.1)O3/MWCNT and 1.79 V vs. RHE for the commercial Pt/C). Full article
(This article belongs to the Topic Electrocatalytic Advances for Sustainable Energy)
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20 pages, 6660 KB  
Review
Roles of Guanidines in Recent Cycloaddition Reactions
by Petar Štrbac, Davor Margetić and Anamarija Briš
Reactions 2026, 7(1), 14; https://doi.org/10.3390/reactions7010014 - 17 Feb 2026
Viewed by 290
Abstract
Guanidines are structurally unique, highly basic, nitrogen-containing organic compounds with strong hydrogen-bonding ability and biological activity, providing valuable functionality in medicinal chemistry, organocatalysis, and materials science. Among modern strategies for assembling guanidine-containing molecules, cycloaddition reactions have emerged as powerful tools due to their [...] Read more.
Guanidines are structurally unique, highly basic, nitrogen-containing organic compounds with strong hydrogen-bonding ability and biological activity, providing valuable functionality in medicinal chemistry, organocatalysis, and materials science. Among modern strategies for assembling guanidine-containing molecules, cycloaddition reactions have emerged as powerful tools due to their efficiency, stereoselectivity, and ability to rapidly build molecular complexity. Recent innovations have expanded cycloaddition methodologies for generating guanidine functionalities, incorporating guanidine-containing substrates, and using guanidine-based catalysts. This review summarizes these advances and highlights the current trends in guanidine-related cycloaddition chemistry. Full article
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27 pages, 3332 KB  
Article
(Co2+,Ni2+)2SiO4 Bimetallic Olivines: An Investigation on the Influence of Molar Ratio Composition of the Ni–Co Olivine System for the Heck–Mizoroki Reaction
by Zanele P. Vundla and Holger B. Friedrich
Reactions 2026, 7(1), 13; https://doi.org/10.3390/reactions7010013 - 14 Feb 2026
Viewed by 286
Abstract
This study systematically investigates the role of Ni in Co2SiO4 in a bimetallic (Co2+,Ni2+)2SiO4 olivine-type system and the materials’ catalytic efficiency in a model Heck–Mizoroki coupling reaction. Thus, a series of olivines with [...] Read more.
This study systematically investigates the role of Ni in Co2SiO4 in a bimetallic (Co2+,Ni2+)2SiO4 olivine-type system and the materials’ catalytic efficiency in a model Heck–Mizoroki coupling reaction. Thus, a series of olivines with varying (Co2+,Ni2+)2SiO4 compositions (0–100% Ni) was synthesised and characterised by ICP-OES, FTIR/Raman, P-XRD and XPS analysis. Ideal mixing of metals was achieved with (49:51) Co:Ni. Catalytic testing revealed distinct conversion vs. time profiles, with the (69:31) Co:Ni olivine exhibiting the best overall performance, combining good reactivity with near-perfect selectivity (>99%) and improved stability. Mechanistic pathways were probed through product scope analysis, reactant–product temporal profiling, leaching and radical scavenging experiments. Results suggest a radical-assisted Heck–Mizoroki mechanism. Spectroscopic data correlated Co2+ and Ni2+ incorporation with M1 and M2 site occupancy, where Ni2+ M2 sites enhanced reactant activation and intermediate stability and Co2+ in the M1 site enhanced product release, though also homocoupling in Co2SiO4. Minimal leaching was observed for all bimetallic catalysts. These findings highlight the tunability of bimetallic olivines for C–C coupling reactions via controlled cation distribution. Full article
(This article belongs to the Special Issue Recent Developments in Heterogeneous Catalysis)
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20 pages, 3274 KB  
Review
Incorporation of Spin Labels and Paramagnetic Tags for Magnetic Resonance Studies Using Cycloaddition Reactions as a Tool
by Amarendra Nath Maity, Amiya Kumar Medda and Shyue-Chu Ke
Reactions 2026, 7(1), 12; https://doi.org/10.3390/reactions7010012 - 6 Feb 2026
Viewed by 358
Abstract
The cycloaddition reaction is one of the most common reactions in organic chemistry. It has been applied in various fields. Herein, we focus on the application of cycloaddition reactions in investigating biological molecules and materials using magnetic resonance techniques. To facilitate magnetic resonance [...] Read more.
The cycloaddition reaction is one of the most common reactions in organic chemistry. It has been applied in various fields. Herein, we focus on the application of cycloaddition reactions in investigating biological molecules and materials using magnetic resonance techniques. To facilitate magnetic resonance studies such as electron paramagnetic resonance (EPR) spectroscopy and paramagnetic nuclear magnetic resonance (NMR) spectroscopy, there is often a requirement to attach spin labels and paramagnetic tags to the system of interest. The cycloaddition reaction is one of the ways to tether these spin labels and paramagnetic tags. In this review, we highlight the applications of various cycloaddition reactions such as the Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC) reaction, the strain-promoted azide–alkyne cycloaddition (SPAAC) reaction and the Diels–Alder reaction in the interdisciplinary field of magnetic resonance studies of biomolecules, including proteins, nucleic acids, carbohydrates, lipids and glycans, as well as materials. Full article
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25 pages, 2708 KB  
Article
Biotechnological Production of Fumaric Acid by Rhizopus arrhizus Using Apple Pomace as Substrate
by Ulf Prüße, Laslo Eidt and Anja Kuenz
Reactions 2026, 7(1), 11; https://doi.org/10.3390/reactions7010011 - 2 Feb 2026
Viewed by 393
Abstract
Fumaric acid is one of the most important bio-based chemicals, with applications in the food, feed, polymer, pulp, and pharmaceutical industries. To overcome the limitations of the current petrochemical production process, alternative methods are being developed. Biotechnological production using wild-type fungi like Rhizopus [...] Read more.
Fumaric acid is one of the most important bio-based chemicals, with applications in the food, feed, polymer, pulp, and pharmaceutical industries. To overcome the limitations of the current petrochemical production process, alternative methods are being developed. Biotechnological production using wild-type fungi like Rhizopus sp. is a promising alternative. In this study, apple pomace was used as a carbohydrate source for fumaric acid production using Rhizopus arrhizus NRRL 1526. Our focus was on the use of free, non-structurally bound carbohydrates present in high amounts in apple pomace originating from direct apple juice processing. Three processes were compared: pressing, extraction, and a combination of both. Two cultivation strategies were applied: pre-culture and separate upstream biomass production. Using the pre-culture approach, a fumaric acid titer of 68.3 g/L was achieved with a yield of 0.53 g/g and a productivity of 0.29 g/(L·h) from synthetic apple pomace juice. Separate biomass production enabled growth-decoupled fumaric acid production, yielding 50.2 g/L and 79.3 g/L with yields of 0.82 g/g and 0.54 g/g and productivities of 0.17 g/(L·h) and 0.27 g/(L·h) from synthetic and real apple pomace juice, respectively. Thus, the efficient use of apple pomace for the fermentative production of fumaric acid is shown. Full article
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16 pages, 4644 KB  
Article
A Quantum Dynamics Simulation of the Adsorption of Water/Oxygen on Perovskite Material
by Jingyang Wu, Jinniu Miao, Yue Wang, Liqian Zhao, Jiaji Liang and Peng Du
Reactions 2026, 7(1), 9; https://doi.org/10.3390/reactions7010009 - 1 Feb 2026
Viewed by 432
Abstract
The stability of perovskite materials in humid conditions significantly hinders their practical deployment. This study employed ab initio molecular dynamics (AIMD) simulations based on the Car–Parrinello approach to elucidate the adsorption mechanisms within two systems: CH3NH3PbI3-15O2 [...] Read more.
The stability of perovskite materials in humid conditions significantly hinders their practical deployment. This study employed ab initio molecular dynamics (AIMD) simulations based on the Car–Parrinello approach to elucidate the adsorption mechanisms within two systems: CH3NH3PbI3-15O2-2H2O and CH3NH3PbI3-15O2-5H2O. The findings indicate that in the system with a higher water content (5H2O), the degradation of the perovskite skeleton is more severe. Additionally, the adsorption energy of oxygen molecules significantly increases, along with more pronounced charge transfer between the oxygen and the perovskite material. The study also reveals that although water molecules contribute to the damage of the perovskite skeleton, oxygen molecules are the primary culprits. These insights not only clarify the specific impacts of various components in a mixed-gas environment on perovskite stability but also provide an essential theoretical basis for future modifications and optimizations of perovskite materials. Full article
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11 pages, 1492 KB  
Article
A Synergistic Dual-Function Silver–Manganese Dioxide–CNTs Ternary Composite Electrocatalyst for Solid-State Zinc–Air Batteries
by Guoqing Zhang and Peng Zhang
Reactions 2026, 7(1), 10; https://doi.org/10.3390/reactions7010010 - 1 Feb 2026
Viewed by 408
Abstract
Exploring effective oxygen reduction reaction (ORR) electrocatalysts is essential for advancing solid-state alkaline zinc–air batteries (ZABs). This paper presents the synthesis of silver–manganese dioxide–carbon nanotubes (SMC) ternary composites as an electrocatalyst for air electrodes, achieved through one-step pyrolysis of silver permanganate under microwave [...] Read more.
Exploring effective oxygen reduction reaction (ORR) electrocatalysts is essential for advancing solid-state alkaline zinc–air batteries (ZABs). This paper presents the synthesis of silver–manganese dioxide–carbon nanotubes (SMC) ternary composites as an electrocatalyst for air electrodes, achieved through one-step pyrolysis of silver permanganate under microwave irradiation. Characterization techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersion spectrometer (EDS) consistently confirmed the composition of SMC, comprising silver and alpha-manganese dioxide anchored on the surface of carbon nanotubes (CNTs). Electrochemical tests including polarization and chronoamperometry curves demonstrated the superior electrocatalytic activity of SMC for ORR compared to chemically produced electrocatalysts in alkaline conditions. Furthermore, the performance of a solid-state zinc–air cell with SMC as the electrocatalyst was evaluated, showing a long discharge voltage plateau and a capacity of 60.03 mAh at 30 mA·cm−2. The study also delves into the mechanism behind the enhanced electrocatalytic activity, concluding that the strategy and electrocatalyst developed in this research offer a promising approach for creating efficient oxygen reduction catalysts for solid-state zinc–air batteries. Full article
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10 pages, 678 KB  
Article
Using the Response Surface Method for the Optimization of Gas-Phase Hydrogenation of Carbon Dioxide on Nickel-Based Catalysts—A Large Laboratory-Scale Process
by Mirosław Krzysztof Szukiewicz, Erwin Górka and Elżbieta Chmiel-Szukiewicz
Reactions 2026, 7(1), 8; https://doi.org/10.3390/reactions7010008 - 23 Jan 2026
Viewed by 292
Abstract
In this study, the response surface method (RSM) was used to determine the best reaction conditions for the gas-phase hydrogenation of carbon dioxide on a commercial nickel-based catalyst. The RSM was applied in our previous study to find the optimal conditions for the [...] Read more.
In this study, the response surface method (RSM) was used to determine the best reaction conditions for the gas-phase hydrogenation of carbon dioxide on a commercial nickel-based catalyst. The RSM was applied in our previous study to find the optimal conditions for the same process carried out in laboratory-scale tubular reactors. The main benefits observed were fast detection of optimal conditions and the high precision of the optimum detected (which was experimentally confirmed). These advantages were due to the small number of experiments conducted and the simplicity of the models employed; only linear and quadratic models were developed. The successful result encouraged us to carry out experiments in a larger-scale reactor—an intermediate between a laboratory plant and a pilot plant. This approach helped us to fix some problems resulting from the larger scale of the process conducted. Despite the difficulties described in the main part of this article, we can recommend using the RSM as a tool for supporting experimentation and substantially speeding up the analysis of results and their introduction into practice. At the process scale considered, maximum carbon dioxide conversion was obtained at a temperature of 354 °C and a ratio of molar fluxes of H2 to CO2 equal to 3.9. It should be emphasized that this result was confirmed experimentally. Full article
(This article belongs to the Special Issue Hydrogen Production and Storage, 3rd Edition)
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13 pages, 2006 KB  
Article
Hydrodeoxygenation of Black Liquor HTL Oil Model Compounds in Supercritical Water
by Sari Rautiainen, Tyko Viertiö, Niko Vuorio, Felix Hyppönen, Luděk Meca, Pavel Kukula and Juha Lehtonen
Reactions 2026, 7(1), 7; https://doi.org/10.3390/reactions7010007 - 20 Jan 2026
Viewed by 303
Abstract
Black liquor, the side stream from Kraft pulping, is a promising feedstock for the production of renewable fuels via hydrothermal liquefaction (HTL). However, further upgrading of the black liquor HTL oil is required to reduce the oxygen content for fuel use. In this [...] Read more.
Black liquor, the side stream from Kraft pulping, is a promising feedstock for the production of renewable fuels via hydrothermal liquefaction (HTL). However, further upgrading of the black liquor HTL oil is required to reduce the oxygen content for fuel use. In this work, the hydrodeoxygenation (HDO) of black liquor HTL oil model compounds was investigated to enhance the understanding of catalyst activity and selectivity under hydrothermal conditions. The study focused on isoeugenol and 4-methylcatechol as model compounds, representing different functionalities in black liquor-derived HTL-oil. Sulfided NiMo catalysts supported on titania, zirconia, activated carbon, and α-alumina were evaluated in batch mode at subcritical and supercritical upgrading using hydrogen gas. The results show that isoeugenol was fully converted in all experiments, while 4-methylcatechol conversion varied depending on the catalyst and reaction conditions. Phenols were obtained as the main products and the maximum degree of deoxygenation achieved was around 40%. This research provides insights into the potential of hydrothermal HDO for upgrading BL-derived biocrudes, emphasising the importance of catalyst selection and reaction conditions in hydrothermal conditions. Full article
(This article belongs to the Special Issue Feature Papers in Reactions in 2025)
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33 pages, 10526 KB  
Review
Recent Developments in the Catalytic Enantioselective Sakurai Reaction
by Hélène Pellissier
Reactions 2026, 7(1), 6; https://doi.org/10.3390/reactions7010006 - 10 Jan 2026
Viewed by 519
Abstract
The Sakurai reaction constitutes a valuable tool for carbon–carbon bond formation. The use of nontoxic allylic reagents as well as the atom economy of the global process has prompted the development of enantioselective (aza)-variants based on the use of chiral organo- and metal [...] Read more.
The Sakurai reaction constitutes a valuable tool for carbon–carbon bond formation. The use of nontoxic allylic reagents as well as the atom economy of the global process has prompted the development of enantioselective (aza)-variants based on the use of chiral organo- and metal catalysts. This review collects the recent developments in catalytic enantioselective Sakurai reactions published since the beginning of 2011, including methodologies based on the use of chiral organocatalysts, metal/boron catalysts and multicatalyst systems. It is divided into three parts, dealing successively with enantioselective organocatalytic (aza)-Sakurai reactions, enantioselective metal/boron-catalyzed Sakurai reactions and enantioselective multicatalyzed (aza)-Sakurai reactions. It shows that, although still widely developed with aromatic aldehydes, the enantioselective catalytic Sakurai reaction has considerably matured in the last decade. Full article
(This article belongs to the Special Issue Feature Papers in Reactions in 2025)
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18 pages, 4662 KB  
Article
Effect of Acetic Acid on Morphology, Structure, Optical Properties, and Photocatalytic Activity of TiO2 Obtained by Sol–Gel
by Sofía Estrada-Flores, Tirso E. Flores-Guia, Catalina M. Pérez-Berumen, Luis A. García-Cerda, Aurora Robledo-Cabrera, Elsa N. Aguilera-González and Antonia Martínez-Luévanos
Reactions 2026, 7(1), 5; https://doi.org/10.3390/reactions7010005 - 10 Jan 2026
Viewed by 533
Abstract
Titanium oxide (TiO2) is of great interest in solar cell manufacturing, hydrogen production, and organic compound photodegradation. The synthesis variables and methodology affect the morphology, texture, crystalline structure, and phase mixtures of TiO2, which, in turn, affect the optical [...] Read more.
Titanium oxide (TiO2) is of great interest in solar cell manufacturing, hydrogen production, and organic compound photodegradation. The synthesis variables and methodology affect the morphology, texture, crystalline structure, and phase mixtures of TiO2, which, in turn, affect the optical and catalytic properties of TiO2. In this work, the effect of acetic acid as a catalyst and chelating agent on the morphology, texture, crystal structure, optical properties, and photocatalytic activity of TiO2 samples obtained using the sol–gel method with sodium dodecyl sulfate (SDS) as a template was investigated. The results indicated that acetic acid not only catalyzes the hydrolysis of the TiO2 precursor but also acts as a chelating agent, causing a decrease in crystallite size from 18.643 nm (T7 sample, pH = 6.8, without addition of acetic acid) to 16.536 nm (T2 sample, pH = 2). At pH 2 and 3, only the anatase phase was formed (T2 and T3 samples), whereas at pH 5 and 6.8, in addition to the anatase phase, the brookite phase (11.4% and 15.61% for samples T5 and T7, respectively) was formed. The band-gap value of TiO2 decreased with decreasing pH during synthesis. Although the T2 sample had the highest specific surface area and pore volume (232.02 m2g−1 and 0.46 gcm−3, respectively), the T3 sample had better efficiency in methylene blue dye photodegradation because its bird-nest-like morphology improved photon absorption, promoting better photocatalytic performance. Full article
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32 pages, 3554 KB  
Review
Synthetic Strategies for Nitramines: From Energetic Materials to Atmospheric Byproducts
by Simen Gjelseth Antonsen, Claus Jørgen Nielsen, Hans Olav Hovtun Palm and Yngve Henning Stenstrøm
Reactions 2026, 7(1), 4; https://doi.org/10.3390/reactions7010004 - 7 Jan 2026
Viewed by 782
Abstract
Nitramines are nitrogen-containing organic compounds with the formula R1R2N–NO2. They are well-known as explosives and have been produced industrially for more than a century. A few nitramine-containing natural products have also been identified in recent years. Nitramines [...] Read more.
Nitramines are nitrogen-containing organic compounds with the formula R1R2N–NO2. They are well-known as explosives and have been produced industrially for more than a century. A few nitramine-containing natural products have also been identified in recent years. Nitramines have also found their way into specific synthetic procedures, usually as intermediates, and for the last decades, the implementation of amine-based carbon capture and storage (CCS) technologies to mitigate CO2 emissions from fossil fuel combustion is of particular concern since small amounts are produced. Both environmental and health implications are of particular interest, and little is known today. The need for efficient and safe synthetic procedures is, therefore, vital for further research in the field. The present review gives a detailed summary of published methods and research post-millennium. Many new as well as well-established methods are presented. Representative examples with basic conditions and yields are given. Finally, indications for future research are discussed. Full article
(This article belongs to the Special Issue Feature Papers in Reactions in 2025)
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36 pages, 6309 KB  
Review
The Kabachnik–Fields Reaction: A Key Transformation in Organophosphorus Chemistry
by Giovanni Ghigo, Sara Nicoletti and Stefano Dughera
Reactions 2026, 7(1), 3; https://doi.org/10.3390/reactions7010003 - 4 Jan 2026
Viewed by 793
Abstract
The Kabachnik–Fields (KF) reaction is a versatile three-component method for the condensation of amines, carbonyl compounds, and P–H reagents, enabling efficient synthesis of α-aminophosphonates—key bioactive and functional molecules. This review critically examines the literature from the last 25 years. However, with regard to [...] Read more.
The Kabachnik–Fields (KF) reaction is a versatile three-component method for the condensation of amines, carbonyl compounds, and P–H reagents, enabling efficient synthesis of α-aminophosphonates—key bioactive and functional molecules. This review critically examines the literature from the last 25 years. However, with regard to mechanistic aspects, selected earlier seminal studies are also considered when necessary to provide a coherent and comprehensive mechanistic framework. Advances in catalyst-free methodologies, sustainable synthetic approaches, and Lewis and Brønsted acid catalysis are discussed, alongside developments in enantioselective KF reactions in the presence of chiral metal complexes or organocatalysts. Full article
(This article belongs to the Special Issue Feature Papers in Reactions in 2025)
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23 pages, 9458 KB  
Article
Experimental Study on the Co-Combustion Characteristics of Brown Gas (HHO) and Bituminous Coal/Anthracite with Different Injection Modes in a One-Dimensional Furnace
by Kaihong Huo, Yunlong Cai, Yong He, Shiyan Liu, Chaoqun Xu, Siyu Liu, Wubin Weng, Yanqun Zhu and Zhihua Wang
Reactions 2026, 7(1), 2; https://doi.org/10.3390/reactions7010002 - 2 Jan 2026
Viewed by 683
Abstract
As the energy structure evolves, low-load operation of coal-fired boilers is becoming common, posing challenges to combustion stability. This study explored the co-combustion of brown gas (HHO) with bituminous coal and anthracite in a one-dimensional furnace. Results indicate that introducing HHO significantly elevated [...] Read more.
As the energy structure evolves, low-load operation of coal-fired boilers is becoming common, posing challenges to combustion stability. This study explored the co-combustion of brown gas (HHO) with bituminous coal and anthracite in a one-dimensional furnace. Results indicate that introducing HHO significantly elevated combustion temperatures, with maximum increases of 158 °C and 207 °C, respectively. In the premixed mode, the flame front shifted upstream, indicating advanced ignition timing. Moreover, HHO co-combustion notably enhanced the combustion stability of anthracite, as reflected in stabilized furnace temperatures. With increasing HHO flow rate, CO concentrations from both bituminous coal and anthracite were reduced by over 80%. The combustion efficiency of bituminous coal reached 98%, while the combustion efficiency of anthracite increased by 19% (premixed) and 13% (staged), confirming the premixed mode’s superiority in promoting complete combustion. HHO co-combustion increased SO2 emissions but had a complex effect on NOX emissions due to the competition between NOX reduction caused by HHO and NOX formation caused by the increased combustion temperature. HHO co-combustion changed the melting point of fly ash, increased the content of Al2O3, and reduced the content of Na2O, K2O, and MgO, influencing the slagging behavior of the boiler and the subsequent management of fly ash. Full article
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22 pages, 938 KB  
Review
Topology Meets Reactivity: Rationalizing Electron Rearrangements in Cycloadditions Through Thom’s Polynomials and Bonding Evolution Theory
by Leandro Ayarde-Henríquez, Cristian J. Guerra, Hans Lenes, Elizabeth Rincón and Eduardo Chamorro
Reactions 2026, 7(1), 1; https://doi.org/10.3390/reactions7010001 - 1 Jan 2026
Cited by 1 | Viewed by 966
Abstract
This mini-review discusses recent advances in the rigorous application of Bonding Evolution Theory (BET) to elucidate electron rearrangements in cycloaddition reactions occurring in both ground and electronically excited states. Computational studies reveal that describing bond formation and cleavage through parametric polynomials derived from [...] Read more.
This mini-review discusses recent advances in the rigorous application of Bonding Evolution Theory (BET) to elucidate electron rearrangements in cycloaddition reactions occurring in both ground and electronically excited states. Computational studies reveal that describing bond formation and cleavage through parametric polynomials derived from the Catastrophe Theory (CT) provides a deeper and more coherent understanding of chemical bonding and reactivity. However, several existing BET applications have adopted CT concepts without fully incorporating the mathematical rigor on which BET is based, resulting in conceptual ambiguities and inaccurate interpretations. A proper implementation of BET requires evaluating the Hessian matrix at potentially degenerate critical points (CPs) of the Electron Localization Function (ELF) and assessing their relative evolution along the reaction coordinate. This systematic protocol integrates key CT principles within BET’s original framework, restoring its formal consistency. The resulting analyses have revealed correlations between electron-density symmetry and CT polynomials, relationships between these polynomials and the homolytic or heterolytic character of bond dissociation, and the development of a CT-based model for scaling bond polarity. These findings demonstrate that incorporating CT-derived functions into BET is not merely a formal refinement but a fundamental step toward achieving a more rigorous and predictive understanding of electron rearrangements in cycloadditions. Full article
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