RSC Mechanochemistry最新文献

Mechanochemistry routinely provides solid forms (polymorphs) that are difficult to obtain by conventional solution-based methods, making it an exciting tool for crystal engineering. However, we are far from identifying the full scope of mechanochemical strategies available to access new and potentially useful solid forms. Using the model organic cocrystal system of nicotinamide (NA) and pimelic acid (PA), we demonstrate with variable temperature ball milling that ball milling seemingly decreases the temperature needed to induce polymorph conversion. Whereas Form I of the NA:PA cocrystal transforms into Form II at 90 °C under equilibrium conditions, the same transition occurs as low as 65 °C during ball milling: a ca 25 °C reduction of the transition temperature. Our results indicate that mechanical energy provides a powerful control parameter to access new solid forms under more readily accessible conditions. We expect this ‘thermo-mechanical’ approach for driving polymorphic transformations to become an important tool for polymorph screening and manufacturing.

Resonant acoustic mixing is a relatively gentle mechanochemical technology that employs pressure waves to induce chemical and morphological transformations. We report here on the production of eleven halogen-bonded (XB) cocrystalline architectures via neat and liquid-assisted resonant acoustic mixing (RAM). Two strong iodinated XB donors, namely 1,4-diiodotetrafluorobenzene (p-DITFB, 1) and 1,3,5-trifluoro-2,4,6-triiodobenzene (sym-TFTIB, 2) each react with five XB donors, namely 2,3,5,6-tetramethylpyrazine (TMP, a), 4-dimethylaminopyridine (DMAP, b), 1,10-phenanthroline (o-Ph, c), 1,10-phenanthroline-5,6-dione (PheDON, d), and 4,5-diazafluoren-9-one (DIZFON, e) to form ten cocrystals. For these systems, it is shown that RAM is capable of producing the same products as are obtained via ball milling. Two novel cocrystals are obtained (of 2d featuring bifurcated XBs, and 2e featuring monofurcated XBs) and their single-crystal X-ray structures are reported. However, an eleventh stoichiomorphic cocrystal of p-DITFB and TMP is obtained exclusively via RAM, suggesting that the combination of RAM and milling approaches may afford a broader exploration of the polymorphic and stoichiomorphic landscape than the use of a single technique in isolation. All products are characterized via powder X-ray diffraction, and ¹³C cross-polarization magic angle spinning (CP/MAS) and ¹⁹F MAS NMR spectroscopy, providing further evidence for the phase purity of samples obtained from RAM experiments and for the degree of polymorphic control available when small volumes of liquid are employed in mechanochemical reactions. This work demonstrates the potential of RAM for the production of known and novel halogen-bonded cocrystalline assemblies, including polymorphic and stoichiomorphic structures.

An iron-free mechanochemical-assisted limonene inverse vulcanization is reported. The process makes use of only limonene and sulphur, industrial waste by-products, under mild conditions (ca. 40 °C) and short time (2 h) using a zirconium oxide reactor and a planetary ball mil. The obtained high value products are light yellow solids, readily soluble in chloroform, optically active oligosulfides, which are different from polysulfides reported under conventional conditions (ca. 185 °C), as confirmed by NMR spectroscopy and mass spectrometry. A general reaction mechanism is proposed, initiated by homolytic sulphur ring opening triggered by mechanical stress, and involving thiirane intermediates, via an addition–elimination reaction of sulphur to the limonene double bonds.

An efficient mechanochemical trimerization of enones with KO^tBu as the base and water as the proton source under solvent-free and ambient conditions has been developed. This protocol provides novel, simple, rapid and scalable access to 1,3,5-triaryl-2,4-acyl-cyclohexanols, which exist as chair conformations with all bulky substituents located at equatorial positions. In addition, the formed cyclohexanol derivatives can be further dehydrated to afford the corresponding cyclohexene derivatives with β,γ-unsaturation. By changing the type or amount of the employed base, another type of stereoisomer, where the 4-acyl group is situated at the axial position, can be favorably generated as the major product.

A mechanochemical base-mediated synthesis of α-ketothioamide from readily available acetophenone derivatives is developed. The reaction is metal-free, solventless, and proceeds in a short reaction time. Importantly, the products differ from those formed under standard solution-based protocols.

Double-network (DN) elastomers are renowned for combining stiffness and toughness. Their exceptional physical properties have garnered significant attention in recent years. However, the fracture phenomena in DN elastomers are much less understood than those in DN gels due to the limited scope of visualization methods. Here, we demonstrate the visualization of sacrificial bond cleavage in DN elastomers during elongation by adding a diarylacetonitrile (DAAN) derivative as a radical-transfer-type fluorescent molecular probe, which enables the visualization of polymer-chain scission without altering the mechanical properties. A tensile test of the DN elastomers that contain DAAN revealed that mechanoradicals are generated from the entire elongated region of the elastomers in the strain-hardening region. In contrast, DN gels generate mechanoradicals only at the necked region. This method is expected to accelerate the investigation of the fracture properties of various DN elastomers.