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18 pages, 2556 KiB

Open AccessArticle

Catalytic Performances of Sn-Beta Catalysts Prepared from Different Heteroatom-Containing Beta Zeolites for the Retro-Aldol Fragmentation of Glucose

by Ricardo Navar, Luca Botti, Giulia Tarantino and Ceri Hammond

Reactions 2022, 3(2), 265-282; https://doi.org/10.3390/reactions3020020 - 12 May 2022

Cited by 2 | Viewed by 2508

Abstract

Beta zeolites with different heteroatoms incorporated into the lattice at two loadings (Si/M = 100 or 200, where M = Al, Fe, Ga, B) were hydrothermally synthesised and used as starting materials for the preparation of Sn-Beta using Solid-State Incorporation. ¹¹⁹Sn CPMG [...] Read more.

Beta zeolites with different heteroatoms incorporated into the lattice at two loadings (Si/M = 100 or 200, where M = Al, Fe, Ga, B) were hydrothermally synthesised and used as starting materials for the preparation of Sn-Beta using Solid-State Incorporation. ¹¹⁹Sn CPMG MAS NMR showed that various Sn species were formed, the distribution of which depended on the identity of the initial heteroatom and the original Si/M ratio. The final Sn-Beta materials (with Si/Sn = 200) were explored as catalysts for the retro-aldol fragmentation of glucose to α-hydroxy-esters in the continuous regime. Amongst these materials, B-derived Sn-Beta was found to exhibit improved levels of selectivity and stability, particularly compared to Sn-Beta catalysts synthesised from commercially available Al-Beta materials, achieving a combined yield of methyl lactate and methyl vinyl glycolate > 80% at short times on the stream. Given that B atoms can be removed from the Beta lattice in mild conditions without the use of highly concentrated acidic media, this discovery demonstrates that B-Beta is an attractive starting material for the future post-synthetic preparation of Lewis acidic zeolites. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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9 pages, 2667 KiB

Open AccessArticle

Calcination Temperature Induced Structural, Optical and Magnetic Transformations in Titanium Ferrite Nanoparticles

by Abhishek Shukla, Subhash C. Singh, Abhishek Bhardwaj, Ravindra Kumar Kotnala, Kailash Narayan Uttam, Chunlei Guo and Ram Gopal

Reactions 2022, 3(1), 224-232; https://doi.org/10.3390/reactions3010017 - 19 Mar 2022

Cited by 2 | Viewed by 3190

Abstract

Titanium ferrite represents one of the most promising magnetic materials that exhibits optical absorption in both ultraviolet and visible spectral regions with a range of applications in photocatalysis, giant magnetoresistance, sensors, high-frequency modern power supplies, etc. Here in the present work, we report [...] Read more.

Titanium ferrite represents one of the most promising magnetic materials that exhibits optical absorption in both ultraviolet and visible spectral regions with a range of applications in photocatalysis, giant magnetoresistance, sensors, high-frequency modern power supplies, etc. Here in the present work, we report synthesizing titanium ferrite NPs via the co-precipitation method. As obtained ferrite nanopowders were characterized using XRD, UV-Visible absorption, Raman scattering, and variable sample magnetometer techniques. The crystalline size of NPs lies between 35 to 50 nm. The as-obtained nanopowder samples were calcined at 200, 500, 800 °C temperatures, and the resulting change in the optical, structural, and magnetic properties are investigated. The saturation magnetization of 500 °C calcined sample is higher than that calcined at 200 °C, but the magnetization value drastically becomes reduced for powder calcined at 800 °C temperature. The results of the present work can be used to understand the effects of annealing temperature on the structural and magnetic properties of other ferrite nanomaterials. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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11 pages, 2638 KiB

Open AccessArticle

Grafting of Cellulose and Microcrystalline Cellulose with Oligo(L-lactic acid) by Polycondensation Reaction

by Md. Hafezur Rahaman, Md. Anamul Haque, Md. Aminur Rahman, Md. Masud Rana, Md. Masud Parvez and S. M. Nur Alam

Reactions 2022, 3(1), 213-223; https://doi.org/10.3390/reactions3010016 - 12 Mar 2022

Cited by 6 | Viewed by 3516

Abstract

Oligo(L-lactic acid) (OLLA) was synthesized by ring opening polymerization of L-lactides using stannous octoate (0.03 wt% of lactide). While this served as the initiator, L-lactic acids were the co-initiators at 140 °C for 10 h, wherein L-lactic acids [...] Read more.

Oligo(L-lactic acid) (OLLA) was synthesized by ring opening polymerization of L-lactides using stannous octoate (0.03 wt% of lactide). While this served as the initiator, L-lactic acids were the co-initiators at 140 °C for 10 h, wherein L-lactic acids were prepared by hydrolytic degradation of L-lactides at 100 °C for 1 h. The molecular weight or degree of polymerization was controlled with monomer/co-initiator ratio (mol/mol). α-cellulose and microcrystalline cellulose (MCC) were extracted from jute fiber by subsequent treatment with sodium chlorite (Na₂ClO₂), NaOH and H₂SO₄. Grafting of OLLA onto α-cellulose and MCC in toluene was carried out using para-toluene sulphonic acid as a catalyst and potassium persulphate (KPS) as an initiator at 130 °C under 380 mm (Hg) pressure for 3, 6, 9, 12, 15, and 18 h. New properties of α-cellulose and MCC were observed due to the successful grafting onto α-cellulose and MCC. Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) were conducted in order to confirm grafting of OLLA onto cellulose and MCC. The FTIR analysis results showed there are some new characteristic absorption peaks appeared (1728 to 1732 cm⁻¹) in the spectrum, which confirmed the grafting of OLLA onto α-cellulose and MCC was successful. SEM images of α-cellulose and MCC before and after grafting revealed significant changes in surface morphology. Grafting of MCC could be more effective for further application in comparison to α-cellulose. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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10 pages, 2162 KiB

Open AccessArticle

Linear-Rate Reactions for the Thermal Devolatilization of Wheat Straw Based on Pseudo-Components

by Carmen Branca

Reactions 2022, 3(1), 203-212; https://doi.org/10.3390/reactions3010015 - 7 Feb 2022

Cited by 2 | Viewed by 2318

Abstract

Thermogravimetric curves are measured in the nitrogen of wheat straw heated up to 773 K with rates between 5–20 K/min. A five-step (or component) parallel reaction scheme was developed for the interpretation of the weight loss characteristics, which makes use of the lumped [...] Read more.

Thermogravimetric curves are measured in the nitrogen of wheat straw heated up to 773 K with rates between 5–20 K/min. A five-step (or component) parallel reaction scheme was developed for the interpretation of the weight loss characteristics, which makes use of the lumped volatile products based on the volatiles released by the pseudo-macrocomponents. The volumetric rates show the usual Arrhenius dependence on temperature and a linear dependence on the mass fraction of the lumped volatile products. The wheat straw devolatilization mechanism consists of a single step for pseud-ocellulose (activation energies of about 180 kJ/mol) and two steps for the pseudohemicellulose, also including extractives, (activation energies of about 101 and 136 kJ/mol) and pseudo-lignin (activation energies of 189 and 126 kJ/mol). For the first two pseudo-macrocomponents, the activation energies were lower than those obtained through a similar approach for beech wood, owing to the much higher content of alkalis acting as catalysts for the decomposition reactions. These occur at lower temperatures and show an enhanced overlap between the pseudo-components. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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11 pages, 3711 KiB

Open AccessCommunication

N-4 Alkyl Cytosine Derivatives Synthesis: A New Approach

by Mauro De Nisco, Antonio Di Maio, Michele Manfra, Carmine Ostacolo, Alessia Bertamino, Pietro Campiglia, Isabel M. Gomez-Monterrey and Silvana Pedatella

Reactions 2022, 3(1), 192-202; https://doi.org/10.3390/reactions3010014 - 6 Feb 2022

Viewed by 3440

Abstract

The selective N-4 alkylation of cytosine plays a critical role in the synthesis of biologically active molecules. This work focuses on the development of practical reaction conditions toward a regioselective synthesis of N-4-alkyl cytosine derivatives. The sequence includes a direct and [...] Read more.

The selective N-4 alkylation of cytosine plays a critical role in the synthesis of biologically active molecules. This work focuses on the development of practical reaction conditions toward a regioselective synthesis of N-4-alkyl cytosine derivatives. The sequence includes a direct and selective sulfonylation at the N-1 site of the cytosine, followed by the alkylation of the amino site using KHMDS in CH₂Cl₂/THF mixture, providing a fast and efficient approach consistent with pyrimidine-based drug design. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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12 pages, 1749 KiB

Open AccessArticle

Photocatalytic Degradation Pathways of the Valsartan Drug by TiO₂ and g-C₃N₄ Catalysts

by Feidias Bairamis and Ioannis Konstantinou

Reactions 2022, 3(1), 160-171; https://doi.org/10.3390/reactions3010012 - 3 Feb 2022

Cited by 3 | Viewed by 2767

Abstract

The photocatalytic degradation of the valsartan (VLS) pharmaceutical using TiO₂ and g-C₃N₄ catalysts under simulated solar light is studied in this paper by high-resolution Orbitrap mass spectrometry. ^•OH radicals were the major oxidant species for the degradation of [...] Read more.

The photocatalytic degradation of the valsartan (VLS) pharmaceutical using TiO₂ and g-C₃N₄ catalysts under simulated solar light is studied in this paper by high-resolution Orbitrap mass spectrometry. ^•OH radicals were the major oxidant species for the degradation of valsartan using TiO₂, while positive holes (h⁺), followed by a much lesser amount of ^•OH radicals, were the major species in the case of g-C₃N₄. Valsartan degradation followed first order kinetics by both catalysts with TiO₂ being the catalyst with the better photocatalytic efficiency. The transformation products (TPs) and their evolution profiles are identified and monitored, respectively, by means of LC-HRMS. Based on TPs identification, the degradation mechanisms are discussed. The major degradation pathways for g-C₃N₄ include decarboxylation and subsequent oxidation, hydroxylation, and cleavage of C–N bond, while for TiO₂ cyclization, TPs are abundant and the hydroxylation occurs in the first stage products. The study highlights the complex nature of TPs formed during such processes, the different mechanisms involved and the necessity for the identification of TPs for the assessment of the treatment and the tracking of such TPs in different environmental compartments. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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12 pages, 2318 KiB

Open AccessArticle

Oxidation of Monoethylene Glycol to Glycolic Acid with Gold-Based Catalyst and Glycolic Acid Isolation by Electrodialysis

by Sarah Tschirner, Eric Weingart, Linda Teevs and Ulf Prüße

Reactions 2022, 3(1), 47-58; https://doi.org/10.3390/reactions3010004 - 28 Dec 2021

Cited by 3 | Viewed by 5959

Abstract

In this work, a highly selective and active gold-based catalyst for the oxidation of high concentrated monoethylene glycol (MEG) in aqueous solution (3 M, 20 wt%) is described. High glycolic acid (GA) selectivity was achieved under mild reaction conditions. The optimization of the [...] Read more.

In this work, a highly selective and active gold-based catalyst for the oxidation of high concentrated monoethylene glycol (MEG) in aqueous solution (3 M, 20 wt%) is described. High glycolic acid (GA) selectivity was achieved under mild reaction conditions. The optimization of the catalyst composition and of the reaction conditions for the oxidation of MEG in semi-batch mode under alkaline conditions led to a GA yield of >80% with a GA selectivity of about 90% in short reaction time. The bimetallic catalyst 0.1 wt% AuPt (9:1)/CeO₂ showed very high activity (>2000 mmol_MEG/g_metalmin) in the oxidation of MEG and, contrary to other studies, an extremely high educt to metal mole ratio of >25,000 was used. Additionally, the gold–platinum catalyst showed a high GA selectivity over more than 10 runs. A very efficient and highly selective process for the GA production from MEG under industrial relevant reaction conditions was established. In order to obtain a GA solution with high purity for the subsequent polymerization, the received reaction solution containing sodium glycolate, unreacted MEG and sodium oxalate is purified by a novel down-stream process via electrodialysis. The overall GA yield of the process exceeds 90% as unreacted MEG can be recycled. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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17 pages, 23208 KiB

Open AccessArticle

Combination of Autohydrolysis and Catalytic Hydrolysis of Biomass for the Production of Hemicellulose Oligosaccharides and Sugars

by Léa Vilcocq, Agnès Crepet, Patrick Jame, Florbela Carvalheiro and Luis C. Duarte

Reactions 2022, 3(1), 30-46; https://doi.org/10.3390/reactions3010003 - 24 Dec 2021

Cited by 9 | Viewed by 3475

Abstract

Three different types of biomass sourced from forestry waste (eucalyptus residues), agricultural waste (wheat straw), and energy crop (miscanthus) were used as starting materials to produce hemicellulosic sugars, furans (furfural and hydroxymethylfurfural), and oligosaccharides. A two-step hybrid process was implemented; biomass was first [...] Read more.

Three different types of biomass sourced from forestry waste (eucalyptus residues), agricultural waste (wheat straw), and energy crop (miscanthus) were used as starting materials to produce hemicellulosic sugars, furans (furfural and hydroxymethylfurfural), and oligosaccharides. A two-step hybrid process was implemented; biomass was first autohydrolysed without any additive to extract hemicelluloses and dissolve it in water. Then, the hydrolysate was treated with a solid acid catalyst, TiO₂-WO_x, in order to achieve hydrolysis and produce monomeric sugars and furans. This article investigates the role of the biomass type, autohydrolysis experimental conditions, polymerisation degree and composition of hemicelluloses on the performance of the process coupling autohydrolysis and catalytic hydrolysis. The highest global yields of both oligosaccharides and monomeric sugars were obtained from Eucalyptus (37% and 18%, respectively). Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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18 pages, 3536 KiB

Open AccessArticle

Thiol-Ene Click-Inspired Late-Stage Modification of Long-Chain Polyurethane Dendrimers

by Dhruba P. Poudel and Richard T. Taylor

Reactions 2022, 3(1), 12-29; https://doi.org/10.3390/reactions3010002 - 22 Dec 2021

Cited by 3 | Viewed by 2837

Abstract

The construction of well-defined polyurethane dendrimers is challenging due to the high reactivity of externally added or in situ formed isocyanates leading to the formation of side products. With a primary focus of dendrimer research being the interaction of the periphery and the [...] Read more.

The construction of well-defined polyurethane dendrimers is challenging due to the high reactivity of externally added or in situ formed isocyanates leading to the formation of side products. With a primary focus of dendrimer research being the interaction of the periphery and the core, we report the synthesis of a common polyurethane dendron, which allows for the late-stage variation of both the periphery and the core. The periphery can be varied simply by installing a clickable unit in the dendron and then attaching to the core and vice-versa. Thus, a common dendron allows for varying periphery and core in the final two steps. To accomplish this, a protecting group-free, one-pot multicomponent Curtius reaction was utilized to afford a robust and versatile AB₂ type polyurethane dendron employing commercially available simple molecules: 5-hydroxyisophthalic acid, 11-bromoundecanol, and 4-penten-1-ol. Subsequent late-stage modifications of either dendrons or dendrimers via a thiol-ene click reaction gave surface-functionalized alternating aromatic-aliphatic polyurethane homodendrimers to generation-three (G3). The dendrons and the dendrimers were characterized by NMR, mass spectrometry, and FT-IR analysis. A bifunctional AB₂ type dendritic monomer demonstrated this approach’s versatility that can either undergo a thiol-ene click or attachment to the core. This approach enables the incorporation of functionalities at the periphery and the core that may not withstand the dendrimer growth for the synthesis of polyurethane dendrimers and other dendritic macromolecules. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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11 pages, 1581 KiB

Open AccessArticle

Kinetic Modeling for the “One-Pot” Hydrogenolysis of Cellulose to Glycols over Ru@Fe₃O₄/Polymer Catalyst

by Oleg Manaenkov, Yuriy Kosivtsov, Valentin Sapunov, Olga Kislitsa, Mikhail Sulman, Alexey Bykov, Alexander Sidorov and Valentina Matveeva

Reactions 2022, 3(1), 1-11; https://doi.org/10.3390/reactions3010001 - 22 Dec 2021

Cited by 5 | Viewed by 2630

Abstract

Despite numerous works devoted to the cellulose hydrogenolysis process, only some of them describe reaction kinetics. This is explained by the complexity of the process and the simultaneous behavior of different reactions. In this work, we present the results of the kinetic study [...] Read more.

Despite numerous works devoted to the cellulose hydrogenolysis process, only some of them describe reaction kinetics. This is explained by the complexity of the process and the simultaneous behavior of different reactions. In this work, we present the results of the kinetic study of glucose hydrogenolysis into ethylene- and propylene glycols in the presence of Ru@Fe₃O₄/HPS catalyst as a part of the process of catalytic conversion of cellulose into glycols. The structure of the Ru-containing magnetically separable Ru@Fe₃O₄/HPS catalysts supported on the polymeric matrix of hypercrosslinked polystyrene was studied to propose the reaction scheme. As a result of this study, a formal description of the glucose hydrogenolysis process into glycols was performed. Based on the data obtained, the mathematical model of the glucose hydrogenolysis kinetics in the presence of Ru@Fe₃O₄/HPS was developed and the parameter estimation was carried out. The synthesized catalyst was found to be characterized by the enhanced magnetic properties and higher catalytic activity in comparison with previously developed catalytic systems (i.e., on the base of SiO₂). The summarized selectivity towards the glycols formation was found to be ca. 42% at 100% of the cellulose conversion in the presence of Ru@Fe₃O₄/HPS. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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13 pages, 1589 KiB

Open AccessArticle

Acid Treated Montmorillonite—Eco-Friendly Clay as Catalyst in Carvone Isomerization to Carvacrol

by Eva Vrbková, Adéla Šímová, Eliška Vyskočilová, Miloslav Lhotka and Libor Červený

Reactions 2021, 2(4), 486-498; https://doi.org/10.3390/reactions2040031 - 18 Nov 2021

Cited by 7 | Viewed by 3457

Abstract

Acid-treated montmorillonites (MMT) were used as catalysts of carvone isomerization to carvacrol. Mineral acids—sulfuric, hydrochloric, nitric acids and organic acids (acetic and chloroacetic)—were used for the acid treatment. Prepared materials were characterized by available characterization methods, namely XRD, EA, TPD, TPO, UV-Vis, laser [...] Read more.

Acid-treated montmorillonites (MMT) were used as catalysts of carvone isomerization to carvacrol. Mineral acids—sulfuric, hydrochloric, nitric acids and organic acids (acetic and chloroacetic)—were used for the acid treatment. Prepared materials were characterized by available characterization methods, namely XRD, EA, TPD, TPO, UV-Vis, laser light scattering and nitrogen physisorption. The structure of montmorillonite remained intact after treatment. However, TPD proved the increase of acidity of acid-treated materials comparing pure montmorillonite. All materials were tested in the isomerization of carvone, producing carvacrol as the desired product. The initial reaction rate increased using the materials in the row MMT-COOH < MMT-HNO₃ < MMT-ClCOOH < MMT-H₂SO₄ < MMT-HCl, which is in accordance with the pKa of acids used for the treatment. The number of weak acid sites strongly influenced the selectivity to carvacrol. The optimal solvent for the reaction was toluene. Total conversion of carvone and the selectivity to carvacrol 95.5% was achieved within 24 h under 80 °C, with toluene as solvent and montmorillonite treated by chloroacetic acid as catalyst. The catalyst may be reused after calcination with only a low loss of activity. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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13 pages, 4122 KiB

Open AccessArticle

Synthesis of a Poly(3-dodecylthiophene) Bearing Aniline Groups for the Covalent Functionalization of Carbon Nanotubes

by Felipe Wasem Klein, Jean-Philippe Lamps, Matthieu Paillet, Pierre Petit and Philippe J. Mésini

Reactions 2021, 2(4), 473-485; https://doi.org/10.3390/reactions2040030 - 11 Nov 2021

Viewed by 2802

Abstract

The functionalization of carbon nanotubes by polymers necessitates two steps, first their modification by oxidizing them or by covalently attaching small compounds to them, then the growth of the polymer chains from these anchors or their grafting onto them. In order to better [...] Read more.

The functionalization of carbon nanotubes by polymers necessitates two steps, first their modification by oxidizing them or by covalently attaching small compounds to them, then the growth of the polymer chains from these anchors or their grafting onto them. In order to better control the process and the rate of functionalization, we develop polymers able to covalently react with the carbon nanotubes by their side chains in one step. We describe the synthesis of a copolymer of dodecylthiophene and its analogue bearing an aniline group at the end of the dodecyl side chain. This copolymer can functionalize single-walled carbon nanotubes (SWNTs) non-covalently and disperse more SWNTs than its hexyl analogues. UV-Vis and fluorescence spectroscopies show that in these non-covalent hybrids, the polymer forms p-stacked aggregates on the SWNTs. The non-covalent hybrids can be transformed into covalent ones by diazonium coupling. In these covalent hybrids the polymer is no longer p-stacked. According to Raman spectroscopy, the conformation of the poly(3-hexylthiophene) backbone is more ordered in the non-covalent hybrids than in the covalent ones. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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15 pages, 2604 KiB

Open AccessArticle

Design of a Compact Microreactor/Heat-Exchanger for a Distributed Production of Liquid Hydrocarbons from Methanol

by Guannan Hu, Nikolay Cherkasov and Evgeny V. Rebrov

Reactions 2021, 2(4), 427-441; https://doi.org/10.3390/reactions2040027 - 18 Oct 2021

Cited by 1 | Viewed by 2879

Abstract

The paper compares conceptual designs of a microstructured reactor/heat-exchanger for the small-scale production of C₈₊ range hydrocarbons from methanol over H-ZSM-5 catalytic coatings. In these designs, air was used as a cooling fluid in the adjacent cooling channels. The heat transfer characteristics [...] Read more.

The paper compares conceptual designs of a microstructured reactor/heat-exchanger for the small-scale production of C₈₊ range hydrocarbons from methanol over H-ZSM-5 catalytic coatings. In these designs, air was used as a cooling fluid in the adjacent cooling channels. The heat transfer characteristics of a single-zone reactor (with channels 500

μ

m in diameter) and a two-zone reactor (with an additional coolant inlet) have been compared. A single reaction zone was not able to reduce the temperature gradient below 15 K, while a two-zone configuration, with a counter-current fluid flow in the upstream section and co-current flow in the downstream section, demonstrated a near-isothermal behaviour, with a mean temperature of 653 K. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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11 pages, 1002 KiB

Open AccessArticle

Interfacial Mass Transfer in Trichloroethylene/Surfactants/ Water Systems: Implications for Remediation Strategies

by Nadia Valletti, Marcello A. Budroni, Istvan Lagzi, Nadia Marchettini, Margarita Sanchez-Dominguez and Federico Rossi

Reactions 2021, 2(3), 312-322; https://doi.org/10.3390/reactions2030020 - 3 Sep 2021

Cited by 4 | Viewed by 2775

Abstract

The fate of dense non-aqueous phase liquids (DNAPLs) in the environment and the consequential remediation problems have been intensively studied over the last 50 years. However, a scarce literature is present about the mass transfer at the DNAPL/water interface. In this paper, we [...] Read more.

The fate of dense non-aqueous phase liquids (DNAPLs) in the environment and the consequential remediation problems have been intensively studied over the last 50 years. However, a scarce literature is present about the mass transfer at the DNAPL/water interface. In this paper, we present a fast method for the evaluation of the mass transfer performance of a surfactant that can easily be employed to support an effective choice for the so-called enhanced remediation strategies. We developed a lab-scale experimental system modelled by means of simple ordinary differential equations to calculate the mass transfer coefficient (K) of trichloroethylene, chosen as representative DNAPL, in the presence and in the absence of two ethoxylated alcohols belonging to the general class of Synperonic surfactants. Our findings revealed that it exists an optimal surfactant concentration range, where K increases up to 40% with respect to pure water. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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11 pages, 1738 KiB

Open AccessArticle

An Upper Limit to O₂ Evolution as Test for Radical and Nonradical Mechanisms for the Fenton Reaction

by Mordechai L. Kremer

Reactions 2021, 2(3), 301-311; https://doi.org/10.3390/reactions2030019 - 2 Sep 2021

Cited by 5 | Viewed by 2998

Abstract

The origin of an upper limit to the amount of O₂ evolved in the rapid reaction between Fe²⁺ and H₂O₂ was investigated at a high concentration of H₂O₂. Using a nonradical model, including the [...] Read more.

The origin of an upper limit to the amount of O₂ evolved in the rapid reaction between Fe²⁺ and H₂O₂ was investigated at a high concentration of H₂O₂. Using a nonradical model, including the formation of a primary Fe²⁺–biperoxy complex with a diminished rate of formation of the active intermediate FeO²⁺, agreement has been reached for the first time with the experimental data obtained by Barb et al. A limited formation of O₂ requires that a finite concentration of H₂O₂ should be present in the reaction mixture when [Fe²⁺] falls to zero. It has been shown that in Barb et al.’s model the condition for such a state ([Fe²⁺] = 0, [H₂O₂] > 0) does not exist. Free radical based models fail as mechanisms for the Fenton reaction. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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17 pages, 5209 KiB

Open AccessArticle

Effect of Pre-Treatment Conditions on the Activity and Selectivity of Cobalt-Based Catalysts for CO Hydrogenation

by Nothando C. Shiba, Xinying Liu, Diane Hildebrandt and Yali Yao

Reactions 2021, 2(3), 258-274; https://doi.org/10.3390/reactions2030016 - 6 Aug 2021

Cited by 7 | Viewed by 2997

Abstract

We investigated the effect of pre-treatment conditions on the activity and selectivity of cobalt catalysts for Fischer–Tropsch synthesis (FTS) by varying both the reduction atmosphere and the reduction temperature. Catalysts supported on SiO₂, Al₂O₃, and TiO₂ [...] Read more.

We investigated the effect of pre-treatment conditions on the activity and selectivity of cobalt catalysts for Fischer–Tropsch synthesis (FTS) by varying both the reduction atmosphere and the reduction temperature. Catalysts supported on SiO₂, Al₂O₃, and TiO₂, prepared via incipient wetness impregnation, were evaluated, and activation temperatures in the range 250–350 °C were considered. Activation with syngas led to a better product selectivity (low CH₄, high selectivity to liquid hydrocarbons, and low paraffin to olefin ratio (P/O)) than the catalysts reduced in H₂ at lower activation temperatures. The Co_xC species suppressed the hydrogenation reaction, and it is hypothesised that this resulted in the high selectivity of olefins observed for the syngas pre-treated catalysts. On the basis of the experimental results, we postulated that a synergistic effect between Co⁰ and Co_xC promotes the production of the long chain hydrocarbons and suppresses the formation of CH₄. In addition, for systems aimed at producing lower olefins, syngas activation is recommended, and for the FTS plants that focus on maximising the production of higher molecular weight products, H₂ activation might be considered. These results provide insights for the future FTS catalyst design and for target product-driven operations. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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13 pages, 2457 KiB

Open AccessArticle

Mechanism of Deoxygenation and Cracking of Fatty Acids by Gas-Phase Cationic Complexes of Ni, Pd, and Pt

by Kevin Parker, Victoria Pho, Richard A. J. O’Hair and Victor Ryzhov

Reactions 2021, 2(2), 102-114; https://doi.org/10.3390/reactions2020009 - 15 May 2021

Cited by 2 | Viewed by 3803

Abstract

Deoxygenation and subsequent cracking of fatty acids are key steps in production of biodiesel fuels from renewable plant sources. Despite the fact that multiple catalysts, including those containing group 10 metals (Ni, Pd, and Pt), are employed for these purposes, little is known [...] Read more.

Deoxygenation and subsequent cracking of fatty acids are key steps in production of biodiesel fuels from renewable plant sources. Despite the fact that multiple catalysts, including those containing group 10 metals (Ni, Pd, and Pt), are employed for these purposes, little is known about the mechanisms by which they operate. In this work, we utilized tandem mass spectrometry experiments (MSⁿ) to show that multiple types of fatty acids (saturated, mono-, and poly-unsaturated) can be catalytically deoxygenated and converted to smaller hydrocarbons using the ternary metal complexes [(phen)M(O₂CR)]⁺], where phen = 1,10-phenanthroline and M = Ni, Pd, and Pt. The mechanistic description of deoxygenation/cracking processes builds on our recent works describing simple model systems for deoxygenation and cracking, where the latter comes from the ability of group 10 metal ions to undergo chain-walking with very low activation barriers. This article extends our previous work to a number of fatty acids commonly found in renewable plant sources. We found that in many unsaturated acids cracking can occur prior to deoxygenation and show that mechanisms involving group 10 metals differ from long-known charge-remote fragmentation reactions. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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Review

Jump to: Research

20 pages, 9140 KiB

Open AccessReview

Synthesis and Reactivity of Cyclic Oxonium Derivatives of nido-Carborane: A Review

by Marina Yu. Stogniy and Igor B. Sivaev

Reactions 2022, 3(1), 172-191; https://doi.org/10.3390/reactions3010013 - 4 Feb 2022

Cited by 8 | Viewed by 2798

Abstract

Nucleophilic ring-opening reactions of cyclic oxonium derivatives of anionic boron hydrides are a convenient method of their modification which opens practically unlimited prospects for their incorporation into various macro- and biomolecules. This contribution provides an overview of the synthesis and reactivity of cyclic [...] Read more.

Nucleophilic ring-opening reactions of cyclic oxonium derivatives of anionic boron hydrides are a convenient method of their modification which opens practically unlimited prospects for their incorporation into various macro- and biomolecules. This contribution provides an overview of the synthesis and reactivity of cyclic oxonium derivatives of nido-carborane as well as half-sandwich complexes based on it. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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21 pages, 3839 KiB

Open AccessReview

Engineering the 2-Oxoglutarate Dehydrogenase Complex to Understand Catalysis and Alter Substrate Recognition

by Joydeep Chakraborty, Natalia Nemeria, Yujeong Shim, Xu Zhang, Elena L. Guevara, Hetal Patel, Edgardo T. Farinas and Frank Jordan

Reactions 2022, 3(1), 139-159; https://doi.org/10.3390/reactions3010011 - 1 Feb 2022

Cited by 3 | Viewed by 3621

Abstract

The E. coli 2-oxoglutarate dehydrogenase complex (OGDHc) is a multienzyme complex in the tricarboxylic acid cycle, consisting of multiple copies of three components, 2-oxoglutarate dehydrogenase (E1o), dihydrolipoamide succinyltransferase (E2o) and dihydrolipoamide dehydrogenase (E3), which catalyze the formation of succinyl-CoA and NADH (+H⁺ [...] Read more.

The E. coli 2-oxoglutarate dehydrogenase complex (OGDHc) is a multienzyme complex in the tricarboxylic acid cycle, consisting of multiple copies of three components, 2-oxoglutarate dehydrogenase (E1o), dihydrolipoamide succinyltransferase (E2o) and dihydrolipoamide dehydrogenase (E3), which catalyze the formation of succinyl-CoA and NADH (+H⁺) from 2-oxoglutarate. This review summarizes applications of the site saturation mutagenesis (SSM) to engineer E. coli OGDHc with mechanistic and chemoenzymatic synthetic goals. First, E1o was engineered by creating SSM libraries at positions His260 and His298.Variants were identified that: (a) lead to acceptance of substrate analogues lacking the 5-carboxyl group and (b) performed carboligation reactions producing acetoin-like compounds with good enantioselectivity. Engineering the E2o catalytic (core) domain enabled (a) assignment of roles for pivotal residues involved in catalysis, (b) re-construction of the substrate-binding pocket to accept substrates other than succinyllysyldihydrolipoamide and (c) elucidation of the mechanism of trans-thioesterification to involve stabilization of a tetrahedral oxyanionic intermediate with hydrogen bonds by His375 and Asp374, rather than general acid–base catalysis which has been misunderstood for decades. The E. coli OGDHc is the first example of a 2-oxo acid dehydrogenase complex which was evolved to a 2-oxo aliphatic acid dehydrogenase complex by engineering two consecutive E1o and E2o components. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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20 pages, 675 KiB

Open AccessReview

Bio-Oil: The Next-Generation Source of Chemicals

by Henrique Machado, Ana F. Cristino, Sofia Orišková and Rui Galhano dos Santos

Reactions 2022, 3(1), 118-137; https://doi.org/10.3390/reactions3010009 - 28 Jan 2022

Cited by 27 | Viewed by 8492

Abstract

Bio-oil, although rich in chemical species, is primarily used as fuel oil, due to its greater calorific power when compared to the biomass from which it is made. The incomplete understanding of how to explore its chemical potential as a source of value-added [...] Read more.

Bio-oil, although rich in chemical species, is primarily used as fuel oil, due to its greater calorific power when compared to the biomass from which it is made. The incomplete understanding of how to explore its chemical potential as a source of value-added chemicals and, therefore, a supply of intermediary chemical species is due to the diverse composition of bio-oil. Being biomass-based, making it subject to composition changes, bio-oil is obtained via different processes, the two most common being fast pyrolysis and hydrothermal liquefaction. Different methods result in different bio-oil compositions even from the same original biomass. Understanding which biomass source and process results in a particular chemical makeup is of interest to those concerned with the refinement or direct application in chemical reactions of bio-oil. This paper presents a summary of published bio-oil production methods, origin biomass, and the resulting composition. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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29 pages, 7276 KiB

Open AccessReview

Thermal Input/Concentration Output Systems Processed by Chemical Reactions of Helicene Oligomers

by Sheng Zhang, Ming Bao and Masahiko Yamaguchi

Reactions 2022, 3(1), 89-117; https://doi.org/10.3390/reactions3010008 - 25 Jan 2022

Cited by 2 | Viewed by 2767

Abstract

This article describes thermal input/concentration output systems processed by chemical reactions. Various sophisticated thermal inputs can be converted into concentration outputs through the double-helix formation of helicene oligomers exhibiting thermal hysteresis. The inputs include high or low temperature, cooling or heating state, slow [...] Read more.

This article describes thermal input/concentration output systems processed by chemical reactions. Various sophisticated thermal inputs can be converted into concentration outputs through the double-helix formation of helicene oligomers exhibiting thermal hysteresis. The inputs include high or low temperature, cooling or heating state, slow or fast cooling state, heating state, and cooling history. The chemical basis for the properties of the chemical reactions includes the reversibility out of chemical equilibrium, sigmoidal relationship and kinetics, bistability involving metastable states, positive feedback by self-catalytic chemical reactions, competitive chemical reactions, and fine tunability for parallel processing. The interfacing of concentration outputs in other systems is considered, and biological cells are considered to have been utilizing such input/output systems processed by chemical reactions. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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17 pages, 8315 KiB

Open AccessReview

The Rearrangement of Alkylallenes to 1,3-Dienes

by Yassir Al-Jawaheri and Marc Colin Kimber

Reactions 2022, 3(1), 70-86; https://doi.org/10.3390/reactions3010006 - 5 Jan 2022

Cited by 3 | Viewed by 3575

Abstract

1,3-Dienes are vital building blocks in organic synthesis. They underpin many fundamental synthetic transformations and are present in numerous natural products and drug candidate molecules. The rearrangement of an alkylallene to a 1,3-diene is an atom efficient, redox neutral, transformation that provides a [...] Read more.

1,3-Dienes are vital building blocks in organic synthesis. They underpin many fundamental synthetic transformations and are present in numerous natural products and drug candidate molecules. The rearrangement of an alkylallene to a 1,3-diene is an atom efficient, redox neutral, transformation that provides a straightforward synthetic route to functionalized 1,3-dienes. Herein, we provide an account of this transformation using allenes that are not predisposed by the presence of heteroatoms or electron-withdrawing groups directly attached to the allene. Early reports of this skeletal rearrangement are acid-mediated approaches, with limited substrate scope, but they provide valuable mechanistic insights. More recent transition metal-mediated approaches that exhibit improved substrate scope are described, together with isolated examples that have utilized this rearrangement. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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15 pages, 3083 KiB

Open AccessReview

Main Group Catalysis: Cationic Si(II) and Ge(II) Compounds as Catalysts in Organosilicon Chemistry

by Elke Fritz-Langhals

Reactions 2021, 2(4), 442-456; https://doi.org/10.3390/reactions2040028 - 19 Oct 2021

Cited by 9 | Viewed by 3505

Abstract

Cyclopentadienyl (Cp)-coordinated cationic Si(II) (1) and Ge(II) compounds (2) are a new class of catalysts for various transformations in organosilicon chemistry. This review demonstrates that these compounds effectively catalyze technically important reactions, such as the hydrosilylation of carbon-carbon multiple [...] Read more.

Cyclopentadienyl (Cp)-coordinated cationic Si(II) (1) and Ge(II) compounds (2) are a new class of catalysts for various transformations in organosilicon chemistry. This review demonstrates that these compounds effectively catalyze technically important reactions, such as the hydrosilylation of carbon-carbon multiple bonds and various types of siloxane-coupling reactions, e.g., the Piers-Rubinsztajn reaction and the oxidative siloxane coupling reaction. Whereas the cationic Si(II) compounds are sensitive to air and moisture, the corresponding cationic Ge(II) compounds are bench stable, thus offering further advantages. The new catalysts contribute to the growing need for the substitution of transition metals and heavier main group metals by their lighter congeners, especially in industrially relevant organosilicon chemistry. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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34 pages, 13479 KiB

Open AccessReview

Benzo[1,2,3]dithiazole Compounds: A History of Synthesis and Their Renewed Applicability in Materials and Synthetic Chemistry, Originating from the Herz Reaction

by Alexander J. Nicholls and Ian R. Baxendale

Reactions 2021, 2(3), 175-208; https://doi.org/10.3390/reactions2030013 - 29 Jun 2021

Cited by 7 | Viewed by 4707

Abstract

The benzo[1,2,3]dithiazole is a unique heteroaromatic functionality whose conjugated profile instils some fascinating electronic properties. This has been historically recognized in the design and manufacture of organic dyes early last century. Although, with the benefit of increased diagnostic techniques and improved understanding, these [...] Read more.

The benzo[1,2,3]dithiazole is a unique heteroaromatic functionality whose conjugated profile instils some fascinating electronic properties. This has been historically recognized in the design and manufacture of organic dyes early last century. Although, with the benefit of increased diagnostic techniques and improved understanding, these structures are attracting greater attention in additional research settings, including applications as organic radicals and semiconductors. In addition, the benzodithiazole functionality has been shown to be a valuable synthetic intermediate in the preparation of a variety of other privileged aromatic and heteroaromatic targets, many of which are important APIs. In this review, the authors aim to critically analyse the potential applicability of these compounds to the fields of not only small-scale laboratory synthetic and medicinal chemistry but also commercial-scale processes and increasingly materials chemistry. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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