Mechanochemistry

Stuart James and Tomislav Friščić

Stuart James is a Professor of Inorganic Chemistry at Queen's University Belfast. Before moving to Belfast he held a Fixed-Term Lectureship at Imperial College London (under Professor Mike Mingos), post-doctoral positions at Cambridge (with Professor Paul Raithby) and Utrecht (with Professor Gerard van Koten) and a Royal Society Post-doctoral Research Fellowship in Strasbourg (with Dr Jean-Pierre Sauvage). He obtained his PhD from The University of Bristol supervised by Professor Paul Pringle. His current research interests are in mechanochemical synthesis and porous liquids.

Tomislav Friščić is an Assistant Professor at McGill University. He received his BSc at the University of Zagreb under the supervision of Branko Kaitner, followed with a PhD at the University of Iowa with Len MacGillivray. He was a post-doctoral associate with William Jones and, from 2008–2011, a Herchel Smith Research Fellow at the University of Cambridge. His research is in the development of catalytic and self-assembly methodologies of solid-state synthesis in diverse areas of organic, metal–organic, pharmaceutical and materials chemistry. He has co-authored over 100 research and review articles and was awarded the 2011 RSC Harrison-Meldola Medal.

It is our pleasure to present this themed issue of Chemical Society Reviews dedicated to mechanochemistry. Over the past decade, the application of mechanical force to chemical systems, either in the form of mechanical grinding and milling, or in the form of ultrasound has resulted in a number of exciting developments and a practical re-discovery of the field.¹ While some of the recent excitement surrounding mechanochemistry is strongly related to its application in relatively young areas of green² and supramolecular chemistry,³ pharmaceutical co-crystals⁴ and metal–organic frameworks,⁵ its applications in more traditional areas of organic synthesis,⁶ catalysis² and inorganic chemistry⁷ are just as exciting and innovative. This diverse and innovative spirit of modern mechanochemical research is well illustrated in the recent web themed issue of Chemical Communications,⁸ which features developments in the mechanochemistry of metal hydrides,⁹ oxides¹⁰ and intermetallic compounds,¹¹ pharmaceutical materials,¹² regioselective and solvent-free organic synthesis,¹³ supramolecular synthesis¹⁴ and catalysis in mechanochemistry.¹⁵

The current collection of review articles, we believe, manages very successfully to simultaneously address this diversity of contemporary mechanochemistry, as well as capture the breadth and fundamentals of the well-established discipline. A historical introduction into the topic has been provided by Laszlo Takacs¹⁶ whose account of The historical development of mechanochemistry (DOI: 10.1039/c2cs35442j) leads us from ancient times to the modern day, and includes a captivating account of mechanochemical science during and immediately after the cold war era. As the transformations of inorganic substances, especially metal oxides and metal alloys,¹⁷ are one of the focal points of mechanochemical research and technological applications, it was highly gratifying to have expert contributions on this topic provided by Šepelák and by Baláž, who each gathered a strong community of experts to create meticulously organised and comprehensive overviews entitled Mechanochemical reactions and syntheses of oxides (DOI: 10.1039/c2cs35462d) and Hallmarks of mechanochemistry: from nanoparticles to technology (DOI: 10.1039/c3cs35468g), respectively. Stepping beyond historical and general perspectives, Hardacre has provided this themed issue with a topical review, Application of heterogeneous catalysts prepared by mechanochemical synthesis (DOI: 10.1039/c3cs60066a), which focuses mainly on recent progress in that area. The experimental tools of mechanochemical synthesis, such as mills, attritors and grinders, are poorly known in the general chemistry community. However, knowledge and understanding of their fundamental parameters in terms of geometry, design, reaction scale-up and energy conversion are increasingly important for the development and application of mechanochemical synthesis. This aspect of mechanochemical research has been addressed in a broad overview of Process engineering with planetary ball mills (DOI: 10.1039/c3cs35455e) by Burmeister and Kwade. To complement overviews of mechanochemistry in the inorganic context, Guan-Wu Wang¹⁸ has provided a comprehensive overview of Mechanochemical organic synthesis (DOI: 10.1039/c3cs35526h) and, together with Zhu and Li, highlighted one of the most exciting areas of organic mechanochemistry, Mechanochemistry of fullerenes and related materials (DOI: 10.1039/c3cs35494f). Although mechanochemical synthesis is often interpreted as chemical synthesis by grinding or milling, such a view is one-sided as there are a number of other means to achieve mechanical activation of molecules, known to lead to new, exciting and rich chemistries.¹⁹ Such alternative types of mechanical activation²⁰ are represented in this themed issue with two expert papers. One of them is the tutorial On the mechanochemical activation by ultrasound (DOI: 10.1039/c2cs35456j) which has been generously provided by Cravotto, Gaudino and Cintas, and we are also greatly indebted to May and Moore for a tutorial on Polymer mechanochemistry: techniques to generate molecular force via elongational flows (DOI: 10.1039/c2cs35463b).

The use of mechanochemical milling and grinding to conduct transformations associated with supramolecular chemistry, such as rearrangements of hydrogen bonds or coordination-driven self-assembly of metal ions and ligands, is often considered novel. However, seeds of this aspect of mechanochemistry can be traced to as early as 1893 in a report by Ling and Baker,²¹ with systematic studies following almost a century later by pioneering groups of solid-state chemistry in the 1980s, such as Paul and Curtin,²² and Toda.²³ This aspect of mechanochemical synthesis is highlighted in this themed issue in an excellent contribution by Braga's²⁴ group on the Mechanochemical preparation of co-crystals (DOI: 10.1039/c3cs60014a).

In our own experience, one of the most frequent questions posed with respect to the recent successes of mechanochemical synthesis is: How does this work? Indeed, the growing diversity of mechanochemical techniques and chemical problems that are being addressed and solved using mechanochemistry points to an urgent need to develop new, sophisticated tools for kinetic and thermodynamic understanding of events taking place under mechanochemical treatment, such as methodologies for reaction monitoring,²⁵ precise assessment of energy balance²⁶ and observing mechanochemical processes at a molecular level.²⁷ It will be increasingly important (although challenging!) to obtain detailed insights and systematical comparisons of diverse mechanochemical systems in search of a bigger picture. This themed issue has provided one of the first steps in that direction, in the form of the review Mechanochemistry of inorganic and organic systems: what is similar, what is different? (DOI: 10.1039/c3cs60052a), kindly provided by Elena Boldyreva.

Notes and references

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