RSC Mechanochemistry最新文献

A new cyclization pattern between arylidene isoxazolones and enamino esters has been demonstrated, efficiently affording various structurally novel cyclopentenyl spiroisoxazolones with high chemoselectivity in a ball mill. Interestingly, the diastereoselectivity of the spiro products is also controllable, with both syn- and anti-isomers generated selectively under different reaction conditions. The mechanochemical protocol features good chemo- and diastereoselectivity, high efficiency, mild reaction conditions and minimal solvent usage, providing rapid, environmentally benign and scalable access to spirocyclopentenes.

A series of layered double hydroxides Mg/Al, MgNi/Al, MgNi/AlIn, MgNiCo/AlIn, MgNiCo/AlInSc, and MgNiCo/AlInScTm were obtained via mechanochemically complemented synthesis with subsequent hydrothermal treatment and additional crystallization. All the samples, except for the Mg/Al one, which was similar to the meixnerite structure, were phase pure. The samples were characterized via X-ray diffraction, FTIR spectroscopy, Raman spectroscopy, and transmission electron microscopy. The peroxidase-like activity of the samples was estimated, and the crystal lattice parameters were calculated. Samples with five, six, and seven cations were characterized by X-ray fluorescence, according to which the cation ratios of the samples and the values of configurational entropy were calculated, which allowed them to be classified as high-entropy materials. For the six-cation sample, elemental mapping was additionally performed, which revealed a uniform distribution of elements over the sample area, along with high-temperature X-ray diffraction, which was also carried out for the five-cation sample.

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In this study, we report the first mechanochemical protocol for highly efficient solvent-free Béchamp reduction using inexpensive Zn metal as a reductant in combination with NH₄Cl. This reaction is considerably faster than previous solution-based reactions. Herein, a variety of nitroarenes were chemoselectively reduced to the corresponding primary aromatic amines in good yields within 30 min. Notably, the present solvent-free protocol does not require an organic solvent or air-sensitive and/or expensive reagents, and all synthetic operations can be performed under ambient conditions, greatly enhancing its practical utility. Furthermore, the feasibility of the gram-scale reaction as well as the synthesis of an important intermediate of the muscle relaxant tizanidine were demonstrated.

Recent research has shown that mechanical energy can trigger dehydrogenation (hydrogen release) from metal and complex hydrides at room temperature, offering an alternative to traditional heat-based methods. This study investigates whether the tribochemical approach can also be effective to release hydrogen from molecular hydrides such as ethane 1,2-diamineborane (EDAB). Surprisingly, despite dehydrogenating at a lower temperature than metal and complex hydrides, EDAB exhibited faint hydrogen release under mechanical stress. To understand this behavior, the tribochemical decomposition pathways of EDAB were investigated using operando Mechanically Stimulated Gas Emission Mass Spectrometry in combination with other surface and material characterization techniques. The lack of hydrogen emission from EDAB is attributed to a combination of strong intramolecular bonds (covalent and dative bonds) within the molecule, and weak intermolecular interactions (hydrogen bonds and van der Waals forces) between EDAB molecules.

In this study, we disclosed that calcium-based heavy Grignard reagents, prepared in situ through a mechanochemical method, reacted with gem-difluorostyrenes in the absence of transition-metal catalysts to afford thermodynamically less favorable (E)-monofluorostilbenes with good to high stereoselectivity. To the best of our knowledge, this is the first example of nucleophilic substitution of a C(sp²)–F bond by an arylcalcium compound.

A new exotridentate ligand, 1,3,5-tris(2-methylpyridin-4-yl)benzene (mTPB), was synthesized and self-assembled with ZnBr₂ in the solid-state via mechanochemistry (i.e., neat grinding (NG)), followed by annealing. The amorphous phase generated by NG transformed into a crystalline structure corresponding to a 2D MOF (1) through an amorphous-to-crystalline transition. Compound 1 contains open 2D layers and exhibited thermal stablility up to 300 °C. Analogous 1,3,5-tris(pyridyl)benzene (TPB), upon NG, formed a poly-[n]-catenane of interlocked (M₁₂L₈) nanocages. This different behaviour was attributed to the presence of the methyl groups in the mTPB ligand.

Here, accompanied by in situ Raman monitoring, we adapt the aza-Michael addition for the formation of the C–N bond under mechanochemical conditions, enabling solvent- and catalyst-free synthesis and facile preparation of compounds that are challenging to obtain in solution.

Ball-milling of addition polymers such as polyolefins, polystyrene and polyacrylates can be used for depolymerization to obtain the respective monomers. However, absolute yields are typically low, especially from polyolefins which are notoriously difficult to depolymerize. To increase the viability of ball milling as a recycling technique, the effect of milling parameters on small hydrocarbon and monomer yields has to be understood. Herein, we systematically investigate the influence of sphere material, milling frequency, plastic filling degree, and milling temperature. Heavy spheres and high milling frequencies boost hydrocarbon yields by maximizing mechanical forces and frequency of collisions. While the dose of kinetic energy is commonly used to describe mechano-chemical processes, we found that it does not capture the mechano-chemical depolymerization of polyolefins. Instead, we rationalized the results based on the Zhurkov equation, a model developed for the thermo-mechanical scission of polymers under stress. In addition, low plastic filling degrees allow for high percentage yields, but cause significant wear on the grinding tools, prohibiting sustained milling. Milling below 40 °C is beneficial for brittle chain cleavage and depolymerization. This study provides a new approach to rationalize the influence of individual milling parameters and their interplay and serves as a starting point to derive design principles for larger-scale mechano-chemical depolymerization processes.

The hexagonal to cubic phase transition of Li₃As was investigated at high pressure and temperature, revealing a cubic high-pressure polymorph in the Li₃Bi structure type. This cubic structure type is preserved in the solid solution of Li₃As–Li₂Se synthesized via mechanochemical ball milling. The solid solutions were investigated via X-ray powder diffraction, showing a linear dependency of the lattice parameter a on the mole fraction of the boundary phases Li₃As and Li₂Se, according to Vegard's law. Configurational entropy is generated by mixed anion lattice occupation between arsenide and selenide and therefore stabilizes the cubic structure of the solid solution. At elevated temperatures, the solid solution of Li₃As–Li₂Se reveals an exsolution process by forming the boundary phases Li₃As and Li₂Se, proving the metastable character of the system. Impedance spectroscopy was used to determine the lithium-ion conductivities in the Li₃As–Li₂Se system, showing significantly higher conductivity values (∼10⁻⁴ to 10⁻⁶ S cm⁻¹ at 50 °C) compared to the pure end members Li₃As (∼10⁻⁷ S cm⁻¹ at 50 °C) and Li₂Se (∼10⁻⁷ S cm⁻¹ at 175 °C).