Following the products of mechanochemical synthesis step by step

Abstract

We describe an experiment in a special device, which permits to quantify the energy input into a solid sample and to follow the products of mechanochemical synthesis step by step. The application of the device is tested on the ''glycine-oxalic acid dihydrate'' system, in which two products are formed concomitantly on co-grinding.Mechanochemical synthesis has been known for at least a century, 1 but the interest in it has grown enormously during the last decade, 2 in particular, in relation to obtaining new organic compounds, salts, and co-crystals. 3 Many examples of successful synthesis achieved on co-grinding a powder mixture in a mortar or in a mill have been described. However, the mechanisms of these transformations remain far from being understood, although several approaches and models have been proposed. The latter are based on considering eutectic melting, 4 dissolution in a small amount of liquid added on cogrinding or present in the reagents as a crystal solvent, 5 a gas-solid reaction resulting from the sublimation of one or more components, 6 and direct solid-state interdiffusion of the components. 2,7 One of the major problems which is intrinsic to the mechanochemical reactions is that a sample is treated not continuously, but in mechanical pulses. As a result, the total time of the mechanical treatment in a mill, or in another mechanical device, differs from the actual time, during which the sample was subjected to mechanical pulses. 2,4b,5a,8 The energy of pulses, their duration, the shape of a pulse, and the time between the pulses are the parameters, which are very important for the reaction outcome. However, it is practically impossible to control them, when either a manual grinding or the treatment in a commonly used mechanical device (a mill, an attritor, an automatic mortar, etc.) is considered. 2,4b,5a,8 In the present communication we describe a model experiment accomplished in a special device designed and manufactured for the detailed studies of mechanochemical reactions in one-or multi-component systems, which enable to treat a sample by individual mechanical pulses of variable and controllable energy, duration, and frequency. 9 This device has been tested on a model system ''glycine-oxalic acid dihydrate'' 10 and allowed us to follow the products of co-grinding formed at the different steps of the transformation.

Clean and Efficient Synthesis Using Mechanochemistry: Coordination Polymers, Metal-Organic Frameworks and Metallodrugs

“…Whereas crystal structure determination from X-ray powder diffraction data is now becoming a reliable method for solvent-free structural characterization of mechanochemically synthesized materials, 43,85 the applicability and understanding of mechanochemical grinding synthesis will benefit from the development of cutting edge techniques including NMR crystallography, 86 crystal structure prediction 87 and terahertz (or phonon) spectroscopy. 16,88 These advanced instrumental and computational techniques, we expect, will complement the ongoing systematic studies 89 of mechanochemical reactivity of molecular materials 90 and inorganic substances 91 and in that way accelerate the unraveling of molecular-level mechanisms underlying grinding mechanosynthesis. This, in turn, should facilitate the greater implementation of mechanochemistry for solvent-free and energy-efficient industrial applications.…”

About the possibilities to detect intermediate stages in mechanochemical synthesis of molecular complexes

“…The reason, why formation of 1 is fast, seems to be related to the crystal structure of 1, which has well optimized interaction between closely spaced molecules, but the structure itself is arranged less efficiently than that of 2, which is ther modynamically more stable. That's why 1 eventually transforms to 2, which happens to be the final product, under appropriate conditions [12]. This idea can be proved not only by the density of 1 which is lower than that of 2 but also by the fact that 1 is the only product of crystallization from aqueous solution of glycine and oxalic acid (even with molar ratio 1 : 1) when an anti solvent technique (precipitation with acetone) is used.…”

“…This idea can be proved not only by the density of 1 which is lower than that of 2 but also by the fact that 1 is the only product of crystallization from aqueous solution of glycine and oxalic acid (even with molar ratio 1 : 1) when an anti solvent technique (precipitation with acetone) is used. On other hand, slow evaporation from the same solution (1 : 1 molar ratio) leads to the formation of 2 [10,12].…”

Different effect of impact and shear mechanical treatment on mechanochemical cocrystallization of piroxicam and succinic acid

“…To verify whether or not the lack of the reaction between piroxicam and succinic acid under shear treatment is due to the decomposition of the succinic acid-piroxicam cocrystal under these conditions, succinic acid-piroxicam cocrystals obtained by dif ferent methods-(a) by crystallization from an aceto nitrile solution, (b) mechanochemically in a mill with dominating impact loading (Retsch Cryomill, 75 min with a drop of ethanol), or (c) with the use of our model apparatus for mainly impact effect [5,6]-were subjected to shear treatment. In all cases, shear treat ment led to the decomposition of the cocrystal phase into two phases of the components (piroxicam and succinic acid), and the mixture acquired a light yellow color typical of piroxicam in the zwitterionic form.…”