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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Organic Chemistry".

Deadline for manuscript submissions: closed (15 November 2019) | Viewed by 65161

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Special Issue Editors

Dr. Vjekoslav Štrukil

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Guest Editor

Ruđer Bošković Institute, Zagreb, Croatia
Interests: mechanochemistry; organic synthesis; green chemistry; solid state photocatalysis; guanidines; (thio)ureas

Dr. Matej Baláž

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Guest Editor

Institute of Geotechnics, Slovak Academy of Sciences, 04001 Košice, Slovakia
Interests: mechanochemistry; ball milling; materials science; natural materials; environmental chemistry; nanoparticle synthesis; adsorption; solid-state synthesis; eggshell; waste treatment; suflides
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Special Issue Information

Dear Colleagues,

In order to face the challenges of modern life, chemists around the world are being engaged in a quest for an efficient and practical, yet sustainable, alternative to synthesis in solution. In this respect, mechanochemical synthesis, recognized as an environmentally-friendly methodology, has enabled the implementation of Green Chemistry Principles and is currently going through its renaissance period. Although mechanical milling has been well known as a processing method in inorganic and materials chemistry for decades, its application in other areas of chemical research largely remained unexplored until breakthrough discoveries in solid state reactivity which took place at the turn of the last century. With liquid-assisted, ion and liquid-assisted and polymer-assisted grinding, as powerful tools to enhance and steer the reactivity of molecules in the solid state, mechanochemical synthesis has found its way into fields of supramolecular chemistry and crystal engineering, pharmaceutical science, metal-organic frameworks, and particularly organic chemistry. However, the „older“ branches of mechanochemistry like inorganic synthesis, catalysis or nanomaterials synthesis are still active. The environmental approach is well documented by many publications connecting mechanochemistry and waste treatment, mechanochemical dehalogenation, hydrogen storage or synthesis of advanced materials for various applications (e.g. energy storage and conversion or biomedical applications). The last 15 years have witnessed an enormous progress in solid state mechanochemistry, which has developed from a curiosity into a well-established synthetic methodology. The phenomenon has turned globally, with the number of research groups dealing with different aspects of mechanochemistry growing each year.

This Special Issue of Molecules is devoted to recent developments in this exciting field and is intended to reflect many exciting faces of mechanochemistry. Contributions reporting on the utilization of mechanochemistry for the synthesis of organic and inorganic molecules, cocrystals, metal-organic frameworks, as well as the studies with strong environmental impact (e.g. waste treatment) and mechanochemcial synthesis of advanced materials, including the mechanistic studies on solid state reactions, are welcome.

Dr. Vjekoslav Štrukil
Dr. Matej Baláž
Guest Editor

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Keywords

mechanochemistry
reaction mechanisms
organic synthesis
crystal engineering
metal-organic frameworks
green chemistry
inorganic synthesis
nanomaterials
advanced materials synthesis
waste treatment

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Published Papers (13 papers)

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Research

11 pages, 2315 KiB

Open AccessFeature PaperArticle

Reaction of Aldoximes with Sodium Chloride and Oxone under Ball-Milling Conditions

by Kuan Chen, Chuang Niu and Guan-Wu Wang

Molecules 2020, 25(16), 3719; https://doi.org/10.3390/molecules25163719 - 14 Aug 2020

Cited by 6 | Viewed by 4550

Abstract

The solvent-free mechanochemical reaction has aroused increasing interest among scientists. Mechanical ball-milling can implement reactions under mild conditions, shorten the reaction time, and improve the reaction efficiency. Particularly, the most attractive characteristic of mechanochemistry is that it can alter the reaction pathway. However, few such examples have been reported so far. In this paper, we report the reaction of aldoximes with NaCl and Oxone under ball-milling conditions to afford N-acyloxyimidoyl chlorides, which are different from those of the liquid-phase counterpart. Full article

(This article belongs to the Special Issue Recent Development of Mechanochemical Synthesis)

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21 pages, 3462 KiB

Open AccessArticle

Exploring the Scope of Macrocyclic “Shoe-last” Templates in the Mechanochemical Synthesis of RHO Topology Zeolitic Imidazolate Frameworks (ZIFs)

by Ivana Brekalo, David E. Deliz, Christopher M. Kane, Tomislav Friščić and K. Travis Holman

Molecules 2020, 25(3), 633; https://doi.org/10.3390/molecules25030633 - 1 Feb 2020

Cited by 4 | Viewed by 4224

Abstract

The macrocyclic cavitand MeMeCH₂ is used as a template for the mechanochemical synthesis of 0.2MeMeCH₂@RHO-Zn₁₆(Cl₂Im)₃₂ (0.2MeMeCH₂@ZIF-71) and RHO-ZnBIm₂ (ZIF-11) zeolitic imidazolate frameworks (ZIFs). It is shown that MeMeCH₂ significantly accelerates the mechanochemical synthesis, providing high porosity products (BET surface areas of 1140 m²/g and 869 m²/g, respectively). Templation of RHO-topology ZIF frameworks constructed of linkers larger than benzimidazole (HBIm) was unsuccessful. It is also shown that cavitands other than MeMeCH₂—namely MeHCH₂, MeiBuCH₂, HPhCH₂, MePhCH₂, BrPhCH₂, BrC5CH₂—can serve as effective templates for the synthesis of x(cavitand)@RHO-ZnIm₂ products. The limitations on cavitand size and shape are explored in terms of their effectiveness as templates. Full article

(This article belongs to the Special Issue Recent Development of Mechanochemical Synthesis)

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9 pages, 3011 KiB

Open AccessCommunication

Exploration of Mechanochemical Activation in Solid-State Fluoro-Grignard Reactions

by Isaiah R. Speight and Timothy P. Hanusa

Molecules 2020, 25(3), 570; https://doi.org/10.3390/molecules25030570 - 28 Jan 2020

Cited by 33 | Viewed by 5503

Abstract

Owing to the strength of the C–F bond, the ‘direct’ preparation of Grignard reagents, i.e., the interaction of elemental magnesium with an organic halide, typically in an ethereal solvent, fails for bulk magnesium and organofluorine compounds. Previously described mechanochemical methods for preparing Grignard reagents have involved ball milling powdered magnesium with organochlorines or bromines. Activation of the C–F bond through a similar route is also possible, however. For example, milling 1- and 2-fluoronaphthalene with an excess of magnesium metal for 2 h, followed by treatment with FeCl₃ and additional milling, produces the corresponding binaphthalenes, albeit in low yields (ca. 20%). The yields are independent of the particular isomer involved and are also comparable to the yields from corresponding the bromonaphthalenes. These results may reflect similar charges that reside on the α-carbon in the naphthalenes, as indicated by density functional theory calculations. Full article

(This article belongs to the Special Issue Recent Development of Mechanochemical Synthesis)

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10 pages, 2831 KiB

Open AccessArticle

A Recyclable, Metal-Free Mechanochemical Approach for the Oxidation of Alcohols to Carboxylic Acids

by Kendra Leahy Denlinger, Preston Carr, Daniel C. Waddell and James Mack

Molecules 2020, 25(2), 364; https://doi.org/10.3390/molecules25020364 - 16 Jan 2020

Cited by 12 | Viewed by 4356

Abstract

The oxidation of primary alcohols under mechanochemical conditions in a Spex8000M Mixer/Mill was investigated. To facilitate ease of separation and recyclability, a polystyrene-bound version of a TEMPO catalyst was employed. When paired with Oxone^® in a stainless-steel vial with a stainless-steel ball, several primary alcohols were successfully oxidized to the corresponding carboxylic acids. The product was isolated using gravity filtration, which also allowed for the polystyrene-bound TEMPO catalyst to be recovered and reused in subsequent oxidation reactions. Furthermore, it was demonstrated that the size and steric hindrance of the primary alcohol does not hinder the rate of the reaction. Finally, the aldehyde was selectively obtained from a primary alcohol under ball milling conditions by using a combination of non-supported TEMPO with a copper vial and copper ball. Full article

(This article belongs to the Special Issue Recent Development of Mechanochemical Synthesis)

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12 pages, 2380 KiB

Open AccessArticle

Efficient Enzymatic Hydrolysis of Biomass Hemicellulose in the Absence of Bulk Water

by Shaghayegh Ostadjoo, Fabien Hammerer, Karolin Dietrich, Marie-Josée Dumont, Tomislav Friscic and Karine Auclair

Molecules 2019, 24(23), 4206; https://doi.org/10.3390/molecules24234206 - 20 Nov 2019

Cited by 37 | Viewed by 3555

Abstract

Current enzymatic methods for hemicellulosic biomass depolymerization are solution-based, typically require a harsh chemical pre-treatment of the material and large volumes of water, yet lack in efficiency. In our study, xylanase (E.C. 3.2.1.8) from Thermomyces lanuginosus is used to hydrolyze xylans from different sources. We report an innovative enzymatic process which avoids the use of bulk aqueous, organic or inorganic solvent, and enables hydrolysis of hemicellulose directly from chemically untreated biomass, to low-weight, soluble oligoxylosaccharides in >70% yields. Full article

(This article belongs to the Special Issue Recent Development of Mechanochemical Synthesis)

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16 pages, 5663 KiB

Open AccessArticle

Insight into the Structure and Properties of Novel Imidazole-Based Salts of Salicylic Acid

by Inês C. B. Martins, Dominik Al-Sabbagh, Klas Meyer, Michael Maiwald, Gudrun Scholz and Franziska Emmerling

Molecules 2019, 24(22), 4144; https://doi.org/10.3390/molecules24224144 - 15 Nov 2019

Cited by 12 | Viewed by 4927

Abstract

The preparation of new active pharmaceutical ingredient (API) multicomponent crystal forms, especially co-crystals and salts, is being considered as a reliable strategy to improve API solubility and bioavailability. In this study, three novel imidazole-based salts of the poorly water-soluble salicylic acid (SA) are reported exhibiting a remarkable improvement in solubility and dissolution rate properties. All structures were solved by powder X-ray diffraction. Multiple complementary techniques were used to solve co-crystal/salt ambiguities: density functional theory calculations, Raman and ¹H/¹³C solid-state NMR spectroscopies. In all molecular salts, the crystal packing interactions are based on a common charged assisted ⁺N-H_(SA)

\dots

O⁻_(co-former) hydrogen bond interaction. The presence of an extra methyl group in different positions of the co-former, induced different supramolecular arrangements, yielding salts with different physicochemical properties. All salts present much higher solubility and dissolution rate than pure SA. The most promising results were obtained for the salts with imidazole and 1-methylimidazole co-formers. Full article

(This article belongs to the Special Issue Recent Development of Mechanochemical Synthesis)

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15 pages, 3805 KiB

Open AccessArticle

Investigation of Potential Amorphisation and Co-Amorphisation Behaviour of the Benzene Di-Carboxylic Acids upon Cryo-Milling

by Rehab Elfakhri and Jonathan C. Burley

Molecules 2019, 24(21), 3990; https://doi.org/10.3390/molecules24213990 - 5 Nov 2019

Cited by 1 | Viewed by 2984

Abstract

Multi-component formulations offer a way to modulate the physico-chemical properties of drug molecules and thereby enhance their efficacy as medicines compared to using only the raw drug, with mechano-chemical synthesis being an increasingly popular way to create these novel materials in a research setting. However, to date studies have focussed on employing pharmaceutically acceptable components, which has led to the literature featuring chemically diverse pairings of drug and excipient. Here we investigate the outcome of cryo-milling and co-cryo-milling of a series of three simple geometrical isomers of benzene di-carboxylic acid with a view to developing a chemically simple model system to investigate areas including cryo-milling, co-cryo-milling, co-amorphous formulation, etc. All three single-component materials exhibit differing behaviour upon cryo-milling and subsequent storage, as do the two-component mixtures. The surprisingly differing behaviours of these chemically similar species upon cryo-milling and co-cryo-milling suggest that molecular chemistry may not be the dominant influence on the outcome of mechano-chemical syntheses, and that other properties should be explored to develop a predictive model for the outcomes of these types of reactions. Full article

(This article belongs to the Special Issue Recent Development of Mechanochemical Synthesis)

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14 pages, 2312 KiB

Open AccessArticle

Phenomenological Inferences on the Kinetics of a Mechanically Activated Knoevenagel Condensation: Understanding the “Snowball” Kinetic Effect in Ball Milling

by Maria Carta, Stuart L. James and Francesco Delogu

Molecules 2019, 24(19), 3600; https://doi.org/10.3390/molecules24193600 - 7 Oct 2019

Cited by 15 | Viewed by 2812

Abstract

We focus on understanding the kinetics of a mechanically activated Knoevenagel condensation conducted in a ball mill, that is characterized by sigmoidal kinetics and the formation of a rubber-like cohesive intermediate state coating the milling ball. The previously described experimental findings are explained using a phenomenological kinetic model. It is assumed that reactants transform into products already at the very first collision of the ball with the wall of the jar. The portion of reactants that are transformed into products during each oscillation is taken to be a fraction of the amount of material that is trapped between the ball and the wall of the jar. This quantity is greater when the reaction mixture transforms from its initial powder form to the rubber-like cohesive coating on the ball. Further, the amount of reactants processed in each collision varies proportionally with the total area of the layer coating the ball. The total area of this coating layer is predicted to vary with the third power of time, thus accounting for the observed dramatic increase of the reaction rate. Supporting experiments, performed using a polyvinyl acetate adhesive as a nonreactive but cohesive material, confirm that the coating around the ball grows with the third power of time. Full article

(This article belongs to the Special Issue Recent Development of Mechanochemical Synthesis)

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19 pages, 1775 KiB

Open AccessArticle

Mechanochemical Synthesis and Isomerization of N-Substituted Indole-3-carboxaldehyde Oximes †

by Matej Baláž, Zuzana Kudličková, Mária Vilková, Ján Imrich, Ľudmila Balážová and Nina Daneu

Molecules 2019, 24(18), 3347; https://doi.org/10.3390/molecules24183347 - 14 Sep 2019

Cited by 15 | Viewed by 5001

Abstract

Performing solution-phase oximation reactions with hydroxylamine hydrochloride (NH₂OH·HCl) carries significant risk, especially in aqueous solutions. In the present study, four N-substituted indole-3-carboxaldehyde oximes were prepared from the corresponding aldehydes by solvent-free reaction with NH₂OH·HCl and a base (NaOH or Na₂CO₃) using a mechanochemical approach, thus minimizing the possible risk. In all cases, the conversion to oximes was almost complete. The focus of this work is on 1-methoxyindole-3-carboxaldehyde oxime, a key intermediate in the production of indole phytoalexins with useful antimicrobial properties. Under optimized conditions, it was possible to reach almost 95% yield after 20 min of milling. Moreover, for the products containing electron-donating substituents (-CH₃, -OCH₃), the isomerization from the oxime anti to syn isomer under acidic conditions was discovered. For the 1-methoxy analog, the acidic isomerization of pure isomers in solution resulted in the formation of anti isomer, whereas the prevalence of syn isomer was observed in solid state. From NMR data the syn and anti structures of produced oximes were elucidated. This work shows an interesting and possibly scalable alternative to classical synthesis and underlines environmentally friendly and sustainable character of mechanochemistry. Full article

(This article belongs to the Special Issue Recent Development of Mechanochemical Synthesis)

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18 pages, 5372 KiB

Open AccessArticle

Mechanochemical Synthesis of CuO/MgAl₂O₄ and MgFe₂O₄ Spinels for Vanillin Production from Isoeugenol and Vanillyl Alcohol

by Behgam Rahmanivahid, Maria Pinilla-de Dios, Mohammad Haghighi and Rafael Luque

Molecules 2019, 24(14), 2597; https://doi.org/10.3390/molecules24142597 - 17 Jul 2019

Cited by 38 | Viewed by 4580

Abstract

CuO/MgAl₂O₄ and CuO/MgFe₂O₄ catalysts were successfully synthesized with the use of spinel supports by a very simple and low-cost mechanochemical method. High-speed ball-milling was used to synthesize these catalyst supports for the first time. Materials were subsequently characterized by using XRD, FESEM, TEM, EDS-Dot mapping, XPS, BET-BJH, and Magnetic Susceptibility to investigate the physical-chemical characteristics of the catalysts. Acidity evaluation results indicated that the catalyst with the Mg-Al spinel support had more acid sites. XRD results showed a successful synthesis of the catalysts with large crystal sizes. Both catalysts were used in isoeugenol oxidation and vanillyl alcohol to vanillin reactions, with the CuO/MgAl₂O₄ showing optimum results. This catalyst provided 67% conversion (74% selectivity) after 2 h and this value improved to 81% (selectivity 100%) with the second reaction after 8 h. The CuO/MgFe₂O₄ catalyst in the first reaction after five hours revealed 53% conversion (47% selectivity) and after eight hours with the second reaction, the conversion value improved to 64% (100% selectivity). In terms of reusability, CuO/MgAl₂O₄ showed better results than the CuO/MgFe₂O₄ catalyst, for both reactions. Full article

(This article belongs to the Special Issue Recent Development of Mechanochemical Synthesis)

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11 pages, 2111 KiB

Open AccessCommunication

Synthesis and Regeneration of A MXene-Based Pollutant Adsorbent by Mechanochemical Methods

by Mohammadtaghi Vakili, Giovanni Cagnetta, Jun Huang, Gang Yu and Jing Yuan

Molecules 2019, 24(13), 2478; https://doi.org/10.3390/molecules24132478 - 5 Jul 2019

Cited by 56 | Viewed by 6537

Abstract

In the present study, an adsorbent material for removal of organic contaminants in wastewater is synthetized by a green and facile mechanochemical method. It is composed of Ti₃C₂T_x MXene layers (obtained by mechanochemical etching of MAX phase with concentrated HF) pillared with terephthalate by rapid direct reaction. Such material shows high specific surface area (135.7 m² g⁻¹) and excellent adsorption capability of methylene blue (209 mg g⁻¹) because of the larger interlayer space among MXene sheets and free carboxylate groups of terephthalate. The spent adsorbent is reutilized (with addition of sole aluminum) to synthetize the MAX phase by mechanochemical procedure, where the terephthalate and the pollutant are carbonized into the carbide. In this way, new MXene-based adsorbent can be re-synthetized for further use. Full article

(This article belongs to the Special Issue Recent Development of Mechanochemical Synthesis)

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14 pages, 3092 KiB

Open AccessFeature PaperArticle

Mechanochemical Synthesis and Characterization of CuInS₂/ZnS Nanocrystals

by Erika Dutková, Nina Daneu, Zdenka Lukáčová Bujňáková, Matej Baláž, Jaroslav Kováč, Jaroslav Kováč, Jr. and Peter Baláž

Molecules 2019, 24(6), 1031; https://doi.org/10.3390/molecules24061031 - 15 Mar 2019

Cited by 15 | Viewed by 4913

Abstract

In this study, CuInS₂/ZnS nanocrystals were synthesized by a two-step mechanochemical synthesis for the first time. In the first step, tetragonal CuInS₂ was prepared from copper, indium and sulphur precursors. The obtained CuInS₂ was further co-milled with zinc acetate dihydrate and sodium sulphide nonahydrate as precursors for cubic ZnS. Structural characterization of the CuInS₂/ZnS nanocrystals was performed by X-ray diffraction analysis, Raman spectroscopy and transmission electron microscopy. Specific surface area of the product (86 m²/g) was measured by low-temperature nitrogen adsorption method and zeta potential of the particles dispersed in water was calculated from measurements of their electrophoretic mobility. Optical properties of the nanocrystals were determined using photoluminescence emission spectroscopy. Full article

(This article belongs to the Special Issue Recent Development of Mechanochemical Synthesis)

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18 pages, 12534 KiB

Open AccessFeature PaperArticle

Mechanochemical Catalytic Transfer Hydrogenation of Aromatic Nitro Derivatives

by Tomislav Portada, Davor Margetić and Vjekoslav Štrukil

Molecules 2018, 23(12), 3163; https://doi.org/10.3390/molecules23123163 - 30 Nov 2018

Cited by 48 | Viewed by 8868

Abstract

Mechanochemical ball milling catalytic transfer hydrogenation (CTH) of aromatic nitro compounds using readily available and cheap ammonium formate as the hydrogen source is demonstrated as a simple, facile and clean approach for the synthesis of substituted anilines and selected pharmaceutically relevant compounds. The scope of mechanochemical CTH is broad, as the reduction conditions tolerate various functionalities, for example nitro, amino, hydroxy, carbonyl, amide, urea, amino acid and heterocyclic. The presented methodology was also successfully integrated with other types of chemical reactions previously carried out mechanochemically, such as amide bond formation by coupling amines with acyl chlorides or anhydrides and click-type coupling reactions between amines and iso(thio)cyanates. In this way, we showed that active pharmaceutical ingredients Procainamide and Paracetamol could be synthesized from the respective nitro-precursors on milligram and gram scale in excellent isolated yields. Full article

(This article belongs to the Special Issue Recent Development of Mechanochemical Synthesis)

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