Reactions

17 pages, 1561 KiB

Open AccessReview

Application of Mixed Potential Theory to Leaching of Mineral Phases

by César A. C. Sequeira

Reactions 2022, 3(2), 312-328; https://doi.org/10.3390/reactions3020023 - 18 Jun 2022

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Leaching is a central unit operation in the hydrometallurgical processing of minerals, which often occurs by means of electrochemical reactions. Application of mixed potential theory to explain the kinetics of oxidative and reductive leaching processes is a useful concept in explaining observed results. [...] Read more.

Leaching is a central unit operation in the hydrometallurgical processing of minerals, which often occurs by means of electrochemical reactions. Application of mixed potential theory to explain the kinetics of oxidative and reductive leaching processes is a useful concept in explaining observed results. Native metals, selected oxides, and most base metal sulfides are electron-conducting phases. For these minerals, leaching may take place by normal corrosion, passivation or galvanic couple mechanisms, which provide individual electrode kinetics enabling the calculation of mixed potentials and overall reaction kinetics. Examples of the electrochemical nature of selected leaching processes are presented and include the effect of mixed potentials, geometry, and associated kinetic reactions. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2022)

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12 pages, 7432 KiB

Open AccessArticle

C-N, C-O and C-S Ullmann-Type Coupling Reactions of Arenediazonium o-Benzenedisulfonimides

by Achille Antenucci and Stefano Dughera

Reactions 2022, 3(2), 300-311; https://doi.org/10.3390/reactions3020022 - 2 Jun 2022

Cited by 5 | Viewed by 3280

Abstract

Arenediazonium o-benzenedisulfonimides have been used as efficient electrophilic partners in Cu(I) catalysed Ullmann-type coupling. The synthetic protocols are mild and easy, and produced either N-alkylanilines, aryl ethers, or thioethers in fairly good yields (18 positive examples, average yield 66%). o-Benzenedisulfonimide was [...] Read more.

Arenediazonium o-benzenedisulfonimides have been used as efficient electrophilic partners in Cu(I) catalysed Ullmann-type coupling. The synthetic protocols are mild and easy, and produced either N-alkylanilines, aryl ethers, or thioethers in fairly good yields (18 positive examples, average yield 66%). o-Benzenedisulfonimide was recovered at the end of the reactions and was reused to prepare the starting salts for further reactions. It is noteworthy that diazonium salts have been used as electrophilic partners in the Ullmann-type protocol for the first time. Full article

(This article belongs to the Special Issue Traditional and Innovative Catalysts for Reactions of Industrial Interest)

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17 pages, 3269 KiB

Open AccessArticle

Valorization of Microcrystalline Cellulose Using Heterogeneous Protonated Zeolite Catalyst: An Experimental and Kinetics Approach

by Samuel Kassaye, Dinesh Gupta, Kamal Kishore Pant and Sapna Jain

Reactions 2022, 3(2), 283-299; https://doi.org/10.3390/reactions3020021 - 30 May 2022

Cited by 2 | Viewed by 1798

Abstract

This study aimed to valorize microcrystalline cellulose (MCC) using protonated zeolite catalysts such as (H-ZSM-5) and Cr/H-ZSM-5 (5%) in ionic liquid. The catalytic effect in synergy with 1-butyl-3-methylimidazolium Chloride ([BMIM] Cl) ionic liquid was studied in detail. The total reducing sugar (TRS) was [...] Read more.

This study aimed to valorize microcrystalline cellulose (MCC) using protonated zeolite catalysts such as (H-ZSM-5) and Cr/H-ZSM-5 (5%) in ionic liquid. The catalytic effect in synergy with 1-butyl-3-methylimidazolium Chloride ([BMIM] Cl) ionic liquid was studied in detail. The total reducing sugar (TRS) was determined using the 3, 5-dinitrisalcylic acid (DNS) array method. The catalysts were characterized using techniques such as Fourier transform infrared (FT-IR), X-ray diffraction analysis (XRD), temperature-programmed desorption of ammonia (NH₃-TPD), and BET-surface area analyzer. H-ZSM-5 effectively depolymerized cellulose with a maximum yield of 70% total reducing sugar (34% glucose, 8% fructose, and 4.5% 5-HMF). Cr/H-ZSM-5 catalyst dehydrated fructose to 5-HMF with a yield of 53%. The use of ionic liquid significantly reduced the activation energy of formation and decomposition. The activation energy determined in cellulose hydrolysis was 85.83 KJ mol⁻¹ for a reaction time of 180 min while the decomposition energy was found to be 42.5 kJ mol⁻¹. Full article

(This article belongs to the Special Issue Catalytic Conversion of Carbonaceous Materials to Fuels and Chemicals)

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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 2124

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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11 pages, 2114 KiB

Open AccessArticle

Regioselective Bond-Forming and Hydrolysis Reactions of Doubly Charged Vanadium Oxide Anions in the Gas Phase

by Chiara Salvitti, Federico Pepi, Anna Troiani and Giulia de Petris

Reactions 2022, 3(2), 254-264; https://doi.org/10.3390/reactions3020019 - 5 Apr 2022

Cited by 1 | Viewed by 1929

Abstract

The gas-phase reactivity of vanadium-containing dianions, NaV₃O₉²⁻ and its hydrated form H₂NaV₃O₁₀²⁻, were probed towards sulphur dioxide at room temperature by ion-molecule reaction (IMR) experiments in the collision cell of an ion [...] Read more.

The gas-phase reactivity of vanadium-containing dianions, NaV₃O₉²⁻ and its hydrated form H₂NaV₃O₁₀²⁻, were probed towards sulphur dioxide at room temperature by ion-molecule reaction (IMR) experiments in the collision cell of an ion trap mass spectrometer. The sequential addition of two SO₂ molecules to the NaV₃O₉²⁻ dianion leads to the breakage of the stable V₃O₉ backbone, resulting in a charge separation process with the formation of new V-O and S-O bonds. On the contrary, the H₂NaV₃O₁₀²⁻ hydroxide species reacts with SO₂, promoting regioselective hydrolysis and bond-forming processes, the latter similar to that observed for the NaV₃O₉²⁻ reactant anion. Kinetic analysis shows that these reactions are fast and efficient with rate constants of the 10⁻⁹ (±30) cm³ s⁻¹ molecule⁻¹ order of magnitude. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2022)

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21 pages, 6076 KiB

Open AccessReview

Recent Progresses in the Preparation of Chlorinated Molecules: Electrocatalysis and Photoredox Catalysis in the Spotlight

by Stefano Parisotto, Emanuele Azzi, Alberto Lanfranco, Polyssena Renzi and Annamaria Deagostino

Reactions 2022, 3(2), 233-253; https://doi.org/10.3390/reactions3020018 - 3 Apr 2022

Cited by 5 | Viewed by 6282

Abstract

Among halogenated molecules, those containing chlorine atoms are fundamental in many areas such as pharmaceuticals, polymers, agrochemicals and natural metabolites. Despite the fact that many reactions have been developed to install chlorine on organic molecules, most of them rely on toxic and hazardous [...] Read more.

Among halogenated molecules, those containing chlorine atoms are fundamental in many areas such as pharmaceuticals, polymers, agrochemicals and natural metabolites. Despite the fact that many reactions have been developed to install chlorine on organic molecules, most of them rely on toxic and hazardous chlorinating reagents as well as harsh conditions. In an attempt to move towards more sustainable approaches, photoredox catalysis and electrocatalysis have emerged as powerful alternatives to traditional methods. In this review, we collect the most recent and significant examples of visible-light- or current-mediated chlorination published in the last five years. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2022)

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Reactions, Volume 3, Issue 2 (June 2022) – 6 articles

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