RESUMO
Typically induced by the mechanical processing of powders in ball mills, mechanochemical transformations are considered to result from the application of mechanical force to solid reactants. However, the undeniable deep connection between the dynamic compaction of powders during impacts and the overall transformation degree has yet to be disclosed. In the present work, we show that the square planar bis(dibenzoylmethanato)NiII coordination compound undergoes trimerization when its powder experiences even a single ball impact. Based on systematic experiments with individual ball impacts and analysis by Raman spectroscopy, we provide here quantitative mapping of the transformation in the powder compact and deduce bulk reaction kinetics from multiple individual impacts.
RESUMO
Using Raman in situ monitoring and mechanochemistry-specific kinetic analysis, we find a correlation between the reaction probability and the Hammett constants in a model mechanochemical reaction of imine formation, indicating that the body of knowledge developed in physical-organic chemistry could be transferable to ball milling reactions in the solid state.
RESUMO
Inelastic collisions of the milling media in ball milling provide energy to the reaction mixture required for chemical transformations. However, movement of the milling media also results in physical mixing of reactants, which may enable a chemical reaction too. Separating the two contributions is challenging and gaining a direct insight into the purely mechanochemically driven reactivity is accordingly hindered. Here, we have applied in situ reaction monitoring by Raman spectroscopy to a suitable, purely mechanically activated, chemical reaction and combined kinetic analysis with numerical simulations to access experimentally unattainable milling parameters. The breadth of milling conditions allows us to establish a linear relationship between the reaction rate and the energy dose received by the sample. Consequently, different kinetic profiles in time scale to the same profile when plotted against the energy dose, which increases with the ball mass, the average ball velocity and the frequency of impacts, but decreases with the hardness of the milling media due to more elastic collisions. The fundamental relationship between kinetics and energy input provides the basis for planning and optimisation of mechanochemical reactions and is essential for transferability of mechanochemical reactions across different milling platforms.