Mechanochemistry

A Practical Introduction from Soft to Hard Materials

Evelina Colacino, Guido Ennas, Ivan Halasz, Andrea Porcheddu, Alessandra Scano, Evelina Colacino, Guido Ennas, Ivan Halasz, Andrea Porcheddu, Alessandra Scano

• Publisher: De Gruyter
• Year: 2020
• ISBN:
  9783110608472
• Edition: 1
• Topic: Tecnologia e ingegneria
• Subtopic: Scienza dei materiali

Mechanochemistry has been recently ackwnoledged by IUPAC as one of the top ten emerging technologies in chemistry, answering to the increased demand for clean processes and sustainable reaction conditions. This book focuses on the rediscovery of mechanochemistry for inorganic, organic and organo-metallic materials. Focus on experimental techniques and equipment will show how to implement mechanochemistry as an innovative way to sustainability in academic laboratories. The contents are ideal for researchers starting off in industry and academia, as well as advanced students.

1 Mechanochemistry: an overview and a historical account

Guido Ennas

Alessandra Scano

Andrea Porcheddu

Ivan Halasz

Evelina Colacino

Introduction

This chapter aims to give a brief overview of the historical development of mechanochemistry, a scientific field that is nowadays becoming very active and promising in materials science and powder technology,¹[a]^–2[a] and also in processing of organic compounds^3–[a]⁴[a] and pharmaceutical formulations.⁵[a]

A description of the most common milling equipment available in academic laboratories for the purposes of research and teaching is highlighted in Chapter 2. Chapter 3 introduces readers to inorganic mechanochemistry, while Chapter 4 reports examples of organic mechanochemical reactions. Examples of mechanochemistry of cocrystals and coordination polymers are highlighted in Chapters 5 and 6, respectively. Topics related to fundamental studies and advanced mechanochemical applications are outside the scope of this book and are not covered here. Interested readers are invited to refer to a more specialized and flourishing literature available in the field.

The term mechanochemistry refers to any chemical reaction that is mechanically induced. According to the International Union of Pure and Applied Chemistry (IUPAC), mechanochemical reaction is defined as Chemical reaction that is induced by the direct absorption of mechanical energy.^5–[b]⁶[a]

More specifically, in the case of solid-state processes, this definition is frequently associated with reactions initiated by any type of mechanical treatment or involving reagents that were pretreated and activated mechanically,⁴[b] to create active sites for chemical reactivity, or increase the active surface of substances that can then more efficiently coalesce and react. Known since millennia,¹[b] mechanochemistry has been recently acknowledged by the IUPAC as one of the top 10 world-changing emerging technologies to enhance chemical synthesis.⁷[a] The growing importance of mechanochemistry has also been recognized by prestigious funding organizations for research and innovation networks in Europe. Indeed, the European Cooperation in Science and Technology (COST)⁸[a] association funded in 2019 the COST Action CA18112 Mechanochemistry for Sustainable Industry (MechSustInd),⁹[a]^–11[a] aiming to foster technological and scientific growth of mechanochemistry across Europe, encompassing academic and industrial partners across 33 European countries and beyond.

Figure 1.1¹²[a] schematizes the development of mechanochemistry, which is chronologically divided into four stages¹[c]: (1) inadvertent mechanochemistry, dating back to the prehistoric time; (2) its recognition as a technique to promote solid-state reactions, occurring during the middle of the nineteenth century; (3) its early development mainly in the field of material science, which includes both the first pioneering investigations on the chemical effects due to mechanical action and the construction of automatic grinders; and (4) the modern period characterized by its extensive application also to new areas of investigations (e.g., pharmaceutical formulation and “medicinal mechanochemistry”¹³[a]) and the development of advanced mechanochemical processes involving the use of additives for polymorphism and reactivity control.¹⁴[a]^–15[a]

Figure 1.1: “Ages” of mechanochemistry. Image reproduced from reference¹²[b] with the permission of Elsevier.

The beginning of inadvertent mechanochemistry dates back into prehistory, where rubbing and grinding were used to prepare foodstuff, to make fire by friction and later to treat minerals, paints and medicines. The earliest known document related to mechanochemistry is found in the book On Stone from the year 315 bc written by Theophrastus of Eresus (who was a student of Aristotle), wherein the reduction of cinnabar (HgS) to mercury by grinding in a copper mortar and pestle is reported. Grinding and its traditional instrument, the mortar and pestle, can be regarded as “the first engineering technology.”¹[d] Despite this earlier discovery, the first systematic studies of mechanochemical reactions were carried out only in the nineteenth century. In 1820, Michael Faraday described the reduction of silver chloride by grinding with zinc, tin, iron and copper in a mortar, and this method was called the “dry way” of inducing reactions.¹⁶[a] He reported that silver chloride reacted with zinc in a fast and highly exothermic reaction. In 1866, Matthew Carey Lea investigated mechanical action to induce a chemical response.¹⁷[a] The most remarkable finding of Lea was related to the decomposition of mercuric and silver chlorides. Both these compounds decomposed while triturated in a mortar, although they were known to melt or sublime upon heating.¹⁸[a] In the same period, Walthère Spring carried out a large-scale systematic study of the mechanical action effects on chemical processes, which anticipated further investigations.¹⁹[a] The main motivation for research endeavors of Spring and Lea was to understand the fundamental nature of chemical reactions under pressure and shear. Grinding, sliding and other forms of mechanical action are important components of many technological processes and they are often accompanied by (unwanted) chemical changes.¹[e]

During the first half of the twentieth century, mechanochemistry went through a slow growth period while its practical potential was recogni...