Iminiumsalze in quantitativen Gas/Festk�per- und Festk�rper/Festk�rper-Reaktionen

Advancing mechanochemical synthesis by combining milling with different energy sources

Owing to its efficiency and unique reactivity, mechanochemical processing of bulk solids has developed into a powerful tool for the synthesis and transformation of various classes of materials. Nevertheless, mechanochemistry is primarily based on simple techniques, such as milling in comminution devices. Recently, mechanochemical reactivity has started being combined with other energy sources commonly used in solution-based chemistry. Milling under controlled temperature, light irradiation, sound agitation or electrical impulses in newly developed experimental setups has led to reactions not achievable by conventional mechanochemical processing. This Perspective describes these unique reactivities and the advances in equipment tailored to synthetic mechanochemistry. These techniques - thermo-mechanochemistry, sono-mechanochemistry, electro-mechanochemistry and photo-mechanochemistry - represent a notable advance in modern mechanochemistry and herald a new level of solid-state reactivity: mechanochemistry 2.0.

Waste-free solid-state syntheses with quantitative yield

Unexpected organic solid-state reactions in the gas-solid and stoichiometric solid-solid versions are highly promising new tools for solvent-free sustainable synthesis and production if they occur with 100% yield. Costly workup is obsolete, no wastes are formed and resources and energy saved. More than 500 published 100%-yield, solid-state reactions in 25 reaction types cover virtually all fields of synthetic organic chemistry. Atomic force microscopy (AFM) reveals that solid-state reactions require long-range molecular movements and are strictly and sensibly guided by the crystal packing. Three steps govern the issue: phase rebuilding, phase transformation, and crystal disintegration (detachment). If one of these fails, or if liquid phases are not avoided, the reaction will usually not run to completion. Repeated creation of fresh contacts of crystallites is essential in solid-solid reactions. New, otherwise inaccessible and highly reactive products are most easily obtained. Cooling below eutectic temperatures, but also thermal activation above room temperature, may be necessary. Liquids may be solidified by cooling or inclusion complexation. Typical single-step, multi-step and cascade reactions have been performed with 100% yield using commonly available starting materials in various fields. Upscaling to the kilogram scale has been achieved under various conditions. Further upscaling to technical size productions seems possible.