RSC Mechanochemistry最新文献

We report a solvent-free mechanochemical approach for the C–H halogenation and nitration of arenes. In situ-generated oxygen-centered mechanoradicals readily oxidize halide or nitrite salts, enabling C–H functionalization of arenes. Radical trapping experiments confirm the involvement of bromine radical species, distinct from conventional solution-phase processes that predominantly proceed via brominium intermediates. This operationally simple and carbon-free strategy is further extended to solid-state vicinal dibromination reactions of unactivated alkenes.

Mechanochemistry has been shown to provide a greener alternative to chemical synthesis; however, challenges in establishing clear relationships between chemical reaction yields and operational reactor parameters, such as milling frequency, milling ball material properties, vessel material properties, and reactor geometries used in a mechanochemical synthesis, make optimizing reactor efficiency difficult. This study presents a force model that relates these reactor parameters to quantifiable impact forces within a vibratory ball mill. To validate this force model, we developed a method for integrated, real-time measurement of force ensembles in the reaction vessel by embedding piezoresistive sensors with fast response to capture impact dynamics at various milling frequencies and operational settings. We measured force using preground NaCl at different fill ratios and compared it to an adjusted Hertzian contact mechanics force model with fill factor. We found agreement between the measured and modeled impact force. At the macroscale, impact acts as an ensemble of forces dynamically applied to the reactants. By simulating the mechanical activation of an illustrative mechanochemical system with known energetics, we show that there is little to no difference in effect between using the mean impact force and force ensemble on the kinetics of a straightforward mechanochemical reaction. We also demonstrate kinetic energy quantification in the Knoevenagel condensation reaction of vanillin and barbituric acid to understand what fraction of kinetic energy goes toward mechanical activation. We observed that the energetics of high-frequency milling for this reaction system entail diminishing returns, reinforcing the notion that there can be an optimal balance between collision intensity, resulting impact forces, and productive energy usage. The developed toolset and models provide a framework for understanding mechanochemical activation in vibratory ball mills and optimizing reaction parameters for scale-up to other reactors.

This paper describes the development of a mechanochemical method for the synthesis of cyclic carbonate esters via CO₂ fixation on propargyl alcohols. This solvent-free process is rapid and occurs under ambient conditions, thus offering a sustainable and efficient alternative to conventional solvent-based protocols. The mechanochemistry, which utilises the energy generated from milling, has the advantage of minimising waste, reducing reaction times, and simplifying work-up. The developed protocol demonstrates broad functional group tolerance, high yields, and the elimination of complex setups, thus highlighting its potential for application in organic and pharmaceutical synthesis.

Mechanochemical synthesis faces reproducibility and scale-up challenges due to complex parameter interactions. This study employs machine learning (ML) to predict NaBH₄ regeneration yield, integrating chemical experimental data and DEM (Discrete Element Method) derived invariant mechanical descriptors (Ē_n, Ē_t, f_col/n_ball). Various algorithms were evaluated, including a two-step modeling strategy to isolate the dominant effect of milling time in our process. Results demonstrate that a two-step Gaussian Process Regression (GPR) model achieves good predictive performance (R² = 0.83), significantly outperforming single-stage models and providing valuable uncertainty estimates. Tree-based ensembles (XGBoost, RF) also benefit from the two-step approach and can enhance interpretability. This work establishes a framework for using ML to optimize mechanochemical processes, reducing experimental cost and offering a method to link mechanical milling conditions to chemical outcomes, thereby enabling predictive mechanochemistry.

Polymorphic transformations in rare-earth sesquioxides (RE-SOs) are accessible via ball-milling. Prolonged mechanical grinding induces the formation of denser polymorphic structures, replicating the phenomena typically observed under high-pressure conditions. In this study, Er₂O₃ cubic phase with bixbyite structure (C-type) was subjected to different milling sessions with diverse vibrational milling frequencies. X-ray diffraction experiments combined with Williamson–Hall (W–H) and Rietveld analysis were adopted to study the microstructural aspects encompassing crystal size, microstrain, and unit cell distortion. As the frequency increased, the transition from the Er₂O₃ cubic to the monoclinic denser structure (B-type) was partially activated. When the milling frequency reached the critical condition, the polymorphic transformation was completely realized. The analysis of the microstructural changes triggered by high frequency milling discloses the key-role of the microstrain, rather than the reduction of the crystal size, in driving the structural transition from cubic to monoclinic polymorphs. Furthermore, ball milling conducted at the highest frequency promotes, rather than amorphization, the formation of the polymorphic form exhibiting a fluorite (CaF₂)-type structure, indicating the presence of point lattice defects involving oxygen vacancies. As a result, the structural analysis revealed the distinct role of microstructural features in promoting polymorphism within RE-SOs.

This review highlights the growing role of mechanochemistry in the synthesis and functionalization of sulfur-based nanomaterials. It begins with a conceptual and historical overview of mechanochemical processes, emphasizing how mechanical energy enables selective bond cleavage, defect formation, and structural transformations in solids. Particular focus is placed on the mechanochemical synthesis of sulfur nanomaterials, where mechanical activation overcomes the inherent chemical inertness of elemental sulfur, promoting the formation of nanodots and other nanostructures. Subsequent sections explore the structural, optical, and photophysical properties of these materials, including light absorption, photoluminescence (PL), optical stability, time-resolved photoluminescence (TRPL), and circularly polarized luminescence (CPL). These properties are strongly influenced by stress-induced defects and crystallinity, which are hallmark features of the mechanochemical approach. The review further surveys a range of application areas such as sensing, catalysis, and energy conversion, where sulfur nanomaterials exhibit promising performance owing to their unique physicochemical properties. In conclusion, we address current challenges, including defect control and the need for a deeper mechanistic understanding, and propose future directions for expanding the scope and enhancing the utility of mechanochemical methods in nanochemistry. Overall, this work underscores the potential of mechanochemistry not only as a green, solvent-free synthesis strategy but also as a powerful platform for uncovering novel functionalities in sulfur-based nanomaterials.

Piezoelectric catalysts were synthesized mechanochemically by converting BaCO₃ and TiO₂ to BaTiO₃, Na₂CO₃ and Nb₂O₅ to NaNbO₃ and Bi₂O₃ and Fe₂O₃ to BiFeO₃. The catalytic reactivity of BaTiO₃, NaNbO₃ and BiFeO₃ was tested using a mechanocatalytic arylation reaction involving 4-nitrobenzenediazonium tetrafluoroborate. The observed activity in the arylation reaction showed a dependence on the abundance of piezoelectrically active anisotropic phases as measured by the pre-edge intensity in XANES spectra of BaTiO₃ and NaNbO₃ and distribution of crystalline phases as measured by XRD for BiFeO₃. A kinetic analysis showed that the reaction over BaTiO₃ was limited by the amount of diazonium salt remaining in the reaction vessel, while the reaction over NaNbO₃ and BiFeO₃ was limited by the generation of electron hole pairs within the piezoelectric structure. This work shows that mechanochemically produced piezocatalysts have superior structural characteristics such as greater relative abundance of anisotropic phases, higher surface areas and smaller particle sizes that led the mechanochemically produced catalysts to outperform piezoelectric commercial counterparts when tested under the same arylation milling conditions.

Herein we present a mechanically induced, solvent-free protocol that sequentially combines the Wittig olefination and Diels–Alder cycloaddition in one-pot and enables the synthesis of structurally complex bicyclic compounds. This method proceeds entirely under ball milling conditions without the requirement of any solvent while eliminating the need for intermediate purification. Careful optimization of the milling parameters and reagent addition enables efficient conversion of various α,β-unsaturated aldehydes and ketones with electron-deficient dienophiles to the corresponding cycloadducts via diene intermediates, demonstrating high stereoselectivity and yielding exclusively endo Diels–Alder adducts. Furthermore, the extension of the sequence by a solvent-free one-pot oxidation is exemplified, achieving a three-step synthesis in a single milling vessel without intermediate workup and purification, which exhibits excellent green metrics in comparison with solution-based methods. This operationally simple and sustainable approach demonstrates the potential of mechanochemistry to streamline multistep organic synthesis, while reducing solvent use and energy demand.

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Ball-milling allowed the efficient realization of asymmetric organocatalytic Michael/aldol cascade, which affords 1′,2′-dihydro-1,2′-binaphthalene derivatives. These compounds were transformed into axially chiral 1,2′-binaphthalene-3′-carbaldehydes under mechanochemical conditions. Evaluation of milling parameters such as frequency or liquid-assisting agents led to optimum reaction conditions, which afforded products in high yields, and short times while preserving high enantiomeric purity.