A kinetic study of mechanically activated atom exchange: the effect of milling frequency and ball mass.

This study investigates the mechanochemical reaction of hydrogen isotope exchange between solid benzoic acid and liquid heavy water. The systematic change of milling conditions revealed that the reaction rate scales with the milling frequency and the mass of the milling balls. The ball size being always the same, faster reactions stem from the use of higher milling frequencies and heavier balls.

Mechanochemical Reactions from Individual Impacts to Global Transformation Kinetics.

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)Ni coordination compound undergoes trimerization when its powder experiences even a single ball impact.

Extending the Hammett correlation to mechanochemical reactions.

Using Raman 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.

Mechanochemical reaction kinetics scales linearly with impact energy.

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.

Conductive Inks Based on Melamine Intercalated Graphene Nanosheets for Inkjet Printed Flexible Electronics.

With the growing number of flexible electronics applications, environmentally benign ways of mass-producing graphene electronics are sought. In this study, we present a scalable mechanochemical route for the exfoliation of graphite in a planetary ball mill with melamine to form melamine-intercalated graphene nanosheets (M-GNS). M-GNS morphology was evaluated, revealing small particles, down to 14 nm in diameter and 0.

Toward Mechanistic Understanding of Mechanochemical Reactions Using Real-Time Monitoring.

The past two decades have witnessed a rapid emergence of interest in mechanochemistry-chemical and materials reactivity achieved or sustained by the action of mechanical force-which has led to application of mechanochemistry to almost all areas of modern chemical and materials synthesis: from organic, inorganic, and organometallic chemistry to enzymatic reactions, formation of metal-organic frameworks, hybrid perovskites, and nanoparticle-based materials. The recent success of mechanochemistry by ball milling has also raised questions about the underlying mechanisms and has led to the realization that the rational development and effective harnessing of mechanochemical reactivity for cleaner and more efficient chemical manufacturing will critically depend on establishing a mechanistic understanding of these reactions. Despite their long history, the development of such a knowledge framework for mechanochemical reactions is still incomplete.

Mechanochemical vs Wet Approach for Directing CO Capture toward Various Carbonate and Bicarbonate Networks.

The distinct research areas related to CO capture and mechanochemistry are both highly attractive in the context of green chemistry. However, merger of these two areas, , mechanochemical CO capture, is still in an early stage of development. Here, the application of biguanidine as an active species for CO capture is investigated using both solution-based and liquid-assisted mechanochemical approaches, which lead to a variety of biguanidinium carbonate and bicarbonate hydrogen-bonded networks.

Mechanistic Insights on the Mechanosynthesis of Phenytoin, a WHO Essential Medicine.

In recent years, mechanochemistry has enriched the toolbox of synthetic chemists, enabling faster and more sustainable access to new materials and existing products, including active pharmaceutical ingredients (APIs). However, molecular-level understanding of most mechanochemical reactions remains limited, delaying the implementation of mechanochemistry in industrial applications. Herein, we have applied in situ monitoring by Raman spectroscopy to the mechanosynthesis of phenytoin, a World Health Organization (WHO) Essential Medicine, enabling the observation, isolation, and characterization of key molecular-migration intermediates involved in the single-step transformation of benzil, urea, and KOH into phenytoin.

Real-Time Observation of "Soft" Magic-Size Clusters during Hydrolysis of the Model Metallodrug Bismuth Disalicylate.

Colloidal bismuth therapeutics have been used for hundreds of years, yet remain mysterious. Here we report an X-ray pair distribution function (PDF) study of the solvolysis of bismuth disalicylate, a model for the metallodrug bismuth subsalicylate (Pepto-Bismol). This reveals catalysis by traces of water, followed by multistep cluster growth.

Using Desmotropes, Cocrystals, and Salts to Manipulate Reactivity in Mechanochemical Organic Reactions.

Performing reactions in the solid state offers the largely unexplored possibility of influencing reactivity by manipulating the solid form of the starting reactants. In this work, we explore the use of various solid forms of barbituric acid and its effect on reaction paths and kinetics in a Knoevenagel condensation reaction with vanillin. Modifications of barbituric acid included the use of its desmotrope, a cocrystal, and a salt as the starting reactant.

Raman spectroscopy for real-time and in situ monitoring of mechanochemical milling reactions.

Solid-state milling has emerged as an alternative, sustainable approach for preparing virtually all classes of compounds and materials. In situ reaction monitoring is essential to understanding the kinetics and mechanisms of these reactions, but it has proved difficult to use standard analytical techniques to analyze the contents of the closed, rapidly moving reaction chamber (jar). Monitoring by Raman spectroscopy is an attractive choice, because it allows uninterrupted data collection from the outside of a translucent milling jar.

A Detailed Kinetico-Mechanistic Investigation on the Palladium C-H Bond Activation in Azobenzenes and Their Monopalladated Derivatives.

Palladium C-H bond activation in azobenzenes with R and R at positions of the phenyl rings (R = NMe, R = H (); R = NMe, R = Cl (); R = NMe, R = I (); R = NMe, R = NO (); R = H, R = H ()) and their monopalladated derivatives, using -[PdCl(DMF)], has been studied in detail by H NMR spectroscopy in -dimethylformamide- (DMF-) at room temperature; the same processes have been monitored in parallel via time-resolved UV-vis spectroscopy in DMF at different temperatures and pressures. The final goal was to achieve, from a kinetico-mechanistic perspective, a complete insight into previously reported reactivity results. The results suggest the operation of an electrophilic concerted metalation-deprotonation mechanism for both the mono- and dipalladation reactions, occurring from the coordination compound and the monopalladated intermediates, respectively.

Mechanochemical Preparation of Active Pharmaceutical Ingredients Monitored by Raman Spectroscopy.

The mechanochemical preparation of silver sulfadiazine and dantrolene, two marketed active pharmaceutical ingredients, was investigated by Raman spectroscopy. For the first time, the mechanochemical transformations involving highly fluorescent compounds could be studied with a high-resolution Raman system combined with a unique suitable Raman probe. Moreover, the kinetic features of the mechanochemical process were examined by a mathematical model allowing to describe the chemical changes under mechanical stress.

DNA-specific selectivity in pairing of model nucleobases in the solid state.

Nucleobases methylated at the glycosidic nitrogen atom achieve DNA-specific self-assembly upon heating in the solid state. We report formation and characterisation of the elusive cocrystal of methylated guanine and methylated cytosine, exhibiting Watson-Crick-type hydrogen bonding, and the crystal structure of 9-methylguanine.

Mechanochemical Metathesis between AgNO and NaX (X = Cl, Br, I) and AgXNO Double-Salt Formation.

Here we describe real-time, monitoring of mechanochemical solid-state metathesis between silver nitrate and the entire series of sodium halides, on the basis of tandem powder X-ray diffraction and Raman spectroscopy monitoring. The mechanistic monitoring reveals that reactions of AgNO with NaX (X = Cl, Br, I) differ in reaction paths, with only the reaction with NaBr providing the NaNO and AgX products directly. The reaction with NaI revealed the presence of a novel, short-lived intermediate phase, while the reaction with NaCl progressed the slowest through the well-defined AgClNO intermediate double salt.

Direct Visualization of a Mechanochemically Induced Molecular Rearrangement.

Recent progress in the field of mechanochemistry has expanded the discovery of mechanically induced chemical transformations to several areas of science. However, a general fundamental understanding of how mechanochemical reactions by ball milling occur has remained unreached. For this, we have now implemented in situ monitoring of a mechanochemically induced molecular rearrangement by synchrotron X-ray powder diffraction, Raman spectroscopy, and real-time temperature sensing.

Direct Mechanocatalysis: Palladium as Milling Media and Catalyst in the Mechanochemical Suzuki Polymerization.

The milling ball is the catalyst. We introduce a palladium-catalyzed reaction inside a ball mill, which makes catalyst powders, ligands, and solvents obsolete. We present a facile and highly sustainable synthesis concept for palladium-catalyzed C-C coupling reactions, exemplarily showcased for the Suzuki polymerization of 4-bromo or 4-iodophenylboronic acid giving poly(para-phenylene).

Isotope Labeling Reveals Fast Atomic and Molecular Exchange in Mechanochemical Milling Reactions.

Using tandem in situ monitoring and isotope-labeled solids, we reveal that mechanochemical ball-milling overcomes inherently slow solid-state diffusion through continuous comminution and growth of milled particles. This process occurs with or without a net chemical reaction and also occurs between solids and liquid additives that can be practically used for highly efficient deuterium labeling of solids. The presented findings reveal a fundamental aspect of milling reactions and also delineate a methodology that should be considered in the study of mechanochemical reaction mechanisms.

Mechanochemical carbon-carbon bond formation that proceeds via a cocrystal intermediate.

We report the first cocrystal as an intermediate in a solid-state organic reaction wherein molecules of barbituric acid and vanillin assume a favorable orientation for the subsequent Knoevenagel condensation.

Mechanism of Mechanochemical C-H Bond Activation in an Azobenzene Substrate by Pd Catalysts.

Mechanism of C-H bond activation by various Pd catalysts under milling conditions has been studied by in situ Raman spectroscopy. Common Pd precursors, that is PdCl , [Pd(OAc) ] , PdCl (MeCN) and [Pd(MeCN) ][BF ] , have been employed for the activation of one or two C-H bonds in an unsymmetrical azobenzene substrate. The C-H activation was achieved by all used Pd precursors and their reactivity increases in the order [Pd(OAc) ] View Article and Find Full Text PDF

Green and rapid mechanosynthesis of high-porosity NU- and UiO-type metal-organic frameworks.

The use of a dodecanuclear zirconium acetate cluster as a precursor enables the rapid, clean mechanochemical synthesis of high-microporosity metal-organic frameworks NU-901 and UiO-67, with surface areas up to 2250 m2 g-1. Real-time X-ray diffraction monitoring reveals that mechanochemical reactions involving the conventional hexanuclear zirconium methacrylate precursor are hindered by the formation of an inert intermediate, which does not appear when using the dodecanuclear acetate cluster as a reactant.

Enthalpy friction: heat flow modelling of unexpected temperature profiles in mechanochemistry of metal-organic frameworks.

Mechanochemical reactions by ball milling are becoming increasingly popular across a wide range of chemical sciences, but understanding and evaluation of temperature during such processes remains a persistent challenge, especially for organic and metal-organic materials. Here, we describe the first methodology for precise real-time measurement of sample temperature during mechanochemical transformations. Using this technique coupled with real-time reaction monitoring by synchrotron X-ray diffraction and numerical simulations of heat flow, we have shown that the temperature profiles of mechanochemical reactions are dominantly determined by the energy dissipated through friction between the sample and the moving milling assembly, while the reaction enthalpy will usually be comparatively insignificant.