RSC Mechanochemistry最新文献

Mechanically induced self-propagating reactions (MSRs) offer the possibility to obtain desired products in an ultrafast and thus cost- and energy-efficient manner. In this work, this is demonstrated for ten binary metal chalcogenides (CdS, CdSe, In₂S₃, NiS, NiSe, PbS, PbSe SnSe, ZnS and ZnSe) by processing mixtures of metals and chalcogens in a planetary ball mill for less than 10 minutes. The MSR process for Ni-based systems is reported for the first time. The studied metals reacted much faster with selenium than with sulfur (with the exception of Ni). The successful MSR occurrence was evidenced by an abrupt increase of gas pressure in the milling jar monitored in situ and subsequently ex situ by X-ray diffraction. The crystallite size of the as-received products was usually in the range 40–260 nm. All the reactions were performed in an air atmosphere, and thus the presence of an inert gas was not necessary. An effort was made to correlate the observed ignition times with the particle size of the precursors, their melting temperature, bulk modulus and thermodynamic parameters (ΔH/C_p and ΔG). While the thermodynamics does not seem to play an important role here, the particle size and bulk modulus of the reacting metal most probably influence the ignition time of MSRs. Namely, higher ductility (low bulk modulus) and finer particles seem to shorten the activation period before the MSR ignition. This study forms a cornerstone for further research in MSRs of metal chalcogenides because it universally assesses the influence of more parameters on the MSR course under fixed milling conditions for different systems. The proposed synthetic pathway also represents an improvement by reducing both time and energy by showing the possibility to reach some of the desired products within a minute-range, being much faster than a classical gradual reaction and further underlines the environmentally benign character of mechanochemistry.

Indium-mediated Barbier allylation exhibited a positive effect with the addition of water under mechanochemical ball-milling conditions. A small amount of water as an additive selectively boosted the allylation of solid-state hydrophobic aldehydes despite their immiscibility. The broad scope and scalability of this method are also demonstrated herein.

Mechanical activation of reactions can reduce significantly the amounts of solvent and energy required to form covalent organic bonds. Despite growing interest in the field of mechanochemistry and increasing reports of mechanochemical synthesis of organic molecules, the fundamental question of how stresses activate covalent-bond-forming (CBF) reactions remains unresolved. This question remains unresolved because of the difficulties involved in measuring the applied forces and the reaction times in mechanochemical reactors, and the challenges related to deconvoluting microscopic (primary) and macroscopic (secondary) processes in the analysis of reaction kinetics. Here we discuss the use nanoscopic probe-microscope tips to explore the kinetics of CBF reactions. Because these experiments examine reactions on monolayers, surfaces, or nanoscopic particles, they circumvent secondary processes to isolate how stress affects the rates of the primary, CBF events. The major result of these studies is an emerging consensus that stress accelerates reactions by distorting organic molecules and in doing so, lowers reaction activation energies and alters reaction trajectories. This new understanding of how stresses activate reactions can be used to predict the outcomes of CBF mechanochemical reactions, which will lead to the wider adoption of sustainable mechanochemical processes by the synthetic community.

Cs₂AgSbCl₆ double perovskite (DP) has been synthesized through many solid-state and solution routes. Still, using unsustainable solvents and complicated synthesis processes are unattractive for large-scale manufacturing. The synthesis of Cs₂AgSbCl₆ using a green approach, mechanosynthesis, offers a sustainable alternative to traditional methods, reducing the environmental impact of solvents and complex processes. X-ray diffraction confirms its double perovskite cubic structure with the space group Fmm (225) and unit cell parameter a = 10.674(2) Å. Diffuse reflectance measurements indicate a slightly smaller indirect band gap (2.61 eV) than chemically synthesized perovskites. The compound demonstrates stability in air and under light. The electronic structure and optical properties of the host material are calculated using quasi-particle theory GW approximation and the Bethe–Salpeter equation (BSE), including the spin–orbit coupling (SOC); the latter is responsible for the emergence of an intermediate conduction band. These findings suggest that double halide perovskite semiconductors, exemplified by the Cs₂AgSbCl₆ DP, can be an eco-friendly alternative to lead halide perovskite semiconductors.

Photoredox catalysis is becoming more and more prevalent in the 21st century as a new tool for organic and polymer synthesis. In addition, this domain clearly fits the expectations of the twelve principles of green chemistry. However, access to metal containing photosensitizers is not always straightforward and can require long reaction times, the use of toxic solvents and multi-step synthesis. These are definitely drawbacks that could be overcome with the use of novel technologies. In this report, we develop a one-pot two-step synthesis of iron(II) photosensitizers using ball-milling. Overall reaction times were drastically reduced, no solvent was needed during the reaction, and ten complexes could be isolated in high yields (73–99%). Using a transparent milling jar, the formation of the complexes could be followed using in situ Raman spectroscopy.

Herein, we propose a simple and fast synthetic strategy for preparing highly crystalline γ-cyclodextrin-based metal–organic frameworks (solid yield 100%). This is the first method that allows metal–organic frameworks with high surface areas to be synthesised without a washing step.

This paper explores the historical significance of milling in various technological areas from ancient times, emphasizing its role beyond the simple ingredient reduction. The study focuses on sources from the 1^st to the 10^th centuries: philologists selected, studied, and translated ancient sources, while chemists provided chemical interpretations by replicating the recipes in the laboratory. The study delves into the synthesis of cinnabar from mercury and sulphur, or mineral ores such as orpiment, realgar, and stibnite. While the mercury–sulphur reaction is known, the synthesis from sulphide ores is not reported in the literature. Chemical replication assessed the reactions' feasibility and confirmed the fundamental role of grinding for the yield of the reaction, which was already recognized by the alchemist Zosimus of Panopolis (3^rd–4^th cent. CE) who claimed “what makes every work perfect is cooking and griding”.

Self-sorting of two imine-based Cu(I) and Fe(II) coordination complexes from a six-component reagent library has been achieved through solvent-free mechanochemistry. The reaction proceeds rapidly, yielding the thermodynamically favored products in less than 24 hours. The results point to the potential of mechanochemistry to achieve increasingly complex multi-metallic systems through one-pot protocols.

Kinetics information on the progress of the mechanochemical reactions is key to their understanding and subsequent scale-up. For crystalline materials, the most robust and tested method for obtaining kinetic data is the Quantitative Phase Analysis (QPA) via Rietveld refinement. In this work, we tested the feasibility of the Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) method on powder X-ray diffraction (PXRD) data of mechanochemical processes by studying the system theophylline (TP) and malonic acid (MA) in a 1 : 1 stoichiometric ratio at different milling conditions. We have highlighted the strengths and weaknesses of the MCR-ALS method, and we demonstrated why it may be an alternative route to obtain quantitative information on mechanochemical kinetics.

Fluorescent radicals have attracted great attention as luminescent materials, mostly on account of their potential to achieve higher luminescence efficiency than closed-shell molecules. However, analyzing fluorescent radicals at ambient conditions remains a challenging task, because radicals are usually unstable in air. In addition, to the best of our knowledge, research aimed at controlling fluorescence wavelengths through substituent changes has not yet been accomplished. Here, we report diverse metastable diarylacetonitrile (DAAN) radicals, which contain different substituents, generated by polymeric mechano-chemical reactions. The DAAN radicals, generated by ball-milling powdered polystyrene together with DAAN derivatives, were dispersed within the polystyrene matrix, where they retained their radical state, which allowed measuring solid-state fluorescence spectra. These measurements revealed that a wide range of fluorescence wavelengths from green to red (λ_em,max = 517–635 nm) can be achieved only by changing the substituents on the aromatic rings in these DAAN radicals. This phenomenon has not been observed for the well-studied triarylmethyl radicals. The fluorescence wavelength of these DAAN radicals can be precisely estimated by time-dependent density-functional theory (TD-DFT) calculations. The amount of DAAN radicals generated upon ball-milling is discussed in conjunction with DFT calculations and experimental results. Our results suggest that the orbital interactions with polymeric mechanoradicals, the bond-dissociation enthalpy, and the steric protection of the radical center are of paramount importance for the generation of DAAN radicals. The results of this study can be expected to provide useful guidelines for the development of advanced fluorescent radicals.