Harnessing mechanochemical effects with ultrasound-induced reactions

Abstract

Chemical reactions may experience numerous and varied effects under the influence of ultrasound. This soft radiation, often viewed as a lab trick, induces and improves both physical and chemical transformations by means of efficient agitation, dissolution, mass and heat transfers, and reagents sonolysis, which all arise from the cavitational collapse. An empirical rationale that distinguishes between true chemical effects and mechanical ones, especially in heterogeneous reactions, was introduced more than two decades ago and has been a useful guidance on reporting sonochemical mechanisms. Recent studies have witnessed a truly remarkable data set that boosts sonochemistry over the wall of applied science. This perspective highlights the importance of the so-called false sonochemistry-closely related to mechanochemistry-in modern synthesis, thus illustrating the advantages of using pressure waves in chemistry. Emphasis is put on green transformations, mild polymerization reactions and the selective cleavage of functionalized polymers, which may have an effective impact in process chemistry and represent a realistic option in industry.

Mechanochemistry in Polymers with Supramolecular Mechanophores

“…Dose-dependent and reversible metal-ligand dissociation occurs upon exposure to ultrasound in solution (Figure 23b, 24a). The absence of ultrasound-induced dissociation of a low-molecular weight model complex and in-depth studies of temperature effects confirm that the dissociation is indeed the result of mechanical activation (for extensive review on sonochemical activation please refer to [11,88]). The influence of the strength of the metal-ligand interactions on the mechanically induced dissociation was also explored.…”

“…The development of such materials systems roots in the realization that a myriad of natural processes happen through weak interactions, [5,6] such as the opening of transmembrane proteins, pre-catalytic enzyme-substrate complexes, or actin polymerization. While some of the early work in the area of polymer mechanochemistry had largely focused fundamental experiments that often involved sonochemical processes in dilute solution, [7][8][9][10][11] there has been a growing interest in solid materials that are capable of selectively transducing macroscopic mechanical forces into molecular events that trigger desirable macroscopic materials responses. [3,9,12,13] Indeed, this emerging design approach has recently permitted the development a range of adaptive solid-state polymers in which pre-programmed functions can be triggered by external stimuli, including mechanical triggers.…”

Interplay Between Mechanochemistry and Sonochemistry

“…Mechanical energy can be harnessed in multiple chemical transformations, such as mechanochromism, analyte detection and self-healing. The basic strategy relies upon the concept of the mechanophore; small structural units embedded into long chain polymers which undergo site-selective scission [6][7][8]12]. Although numerous solid-state and solution methods can be used to activate polymers [11], sonication holds the unique ability of providing shear forces and strain in solution by virtue of the mechanical events associated with cavitational collapse.…”

“…This chapter aims to describe the mechanical bias of cavitational effects and how they are related to conventional mechanochemistry and force-induced physical fields in general. This subject has been well documented over the last decade [5][6][7][8][9], and particular attention has been paid to scenarios such as mechanically responsive polymers [10][11][12], micro-and nano-structured materials [13][14][15], and sonocrystallization [16], which are all expected to have a major impact on the fabrication of novel and smart materials as well as the pharmaceutical industry. Although we shall briefly mention these past achievements, our goal is to focus on the aspects of sono-mechanochemistry that have been overlooked in recent thematic issues.…”

Sonoluminescence and sonochemiluminescence from a microreactor

“…This is influenced by altering the power input to the system and the number of pits. The areas of potential application for these findings are many; to name a few we consider the ultrapurification of water for fine chemicals or phar-maceutical uses, mechanochemistry and the selective cleaning of circuit boards in which localized cavitation can avoid the damage of certain components with conventional sonication systems (G. Cravotto, 2012;Cobley et al, 2011). Our results can be of importance to existing non destructive testing and inspection of surfaces with localized fluorescent dye penetration which are improved by the action of localized cavitation(N.V. Dezhkunov, 2005).…”