Mechanochemical reactions tracked in real time
This mechanical mill contains steel ball bearings that grind solid reactants into a powder, increasing the surface area but also providing structural deformations that drive chemical reactions forward. Such equipment could provide new routes to synthetic chemicals that bypass hazardous catalysts or solvents. Video courtesy Tomislav Friščić
By Tyler Irving
Posted January 2013
A McGill chemist has become the first to track the progress of a reaction that involves mechanical milling in real time through the use of x-ray diffraction. The technique represents an important step forward for the field of mechanochemistry, which seeks to synthesize chemical substances without solvents or catalysts.
Mechanochemical processes typically involve a reaction vessel filled with grinding media such as steel ball bearings. Rapid shaking of the vessel causes these balls to grind one or more of the reactants into powder. “The energy imposed by mechanical action leads to a structural deformation of the material, which provides the driving force for the chemical reaction,” explains Tomislav Friščić, now a professor at McGill University. Previous attempts to monitor mechanochemical reactions provided a skewed picture, since the milling had to be stopped periodically to take samples.
For their latest publication in Nature Chemistry, Friščić and his team brought a modified milling apparatus to the European Synchrotron Radiation Facility in Grenoble, France where they used x-ray radiation that was hard enough to get through the three-millimetre thick steel walls of the milling vessel, but soft enough to interact with the components inside. This allowed the researchers to visualize the reaction’s progress in real time. “When we started collecting data, we just couldn’t believe how beautiful it was,” says Friščić. “You can actually observe how the signals of your reactants, products and intermediates appear and disappear, sometimes within seconds.” Now that proof of concept has been demonstrated, Friščić hopes to apply the technique to other mechanochemical syntheses, including nanoparticles and potential pharmaceutical compounds.
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