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Researchers make major breakthrough in field of green chemistry

Researchers at McGill University may have discovered a better way to make chemicals. Bulk solvents, which are used universally in the chemical industry, are extremely bad for humans and the environment. As a result, there is a growing interest in relying on “mechanochemistry” as an alternative to bulk solvents. Mechanochemistry uses high-frequency milling to drive reactions. The underlying chemistry, however, is difficult to observe because milling involves the intense impacts of steel balls in quickly moving jars.

Researchers at McGill have had a breakthrough in understanding mechanochemistry. They have observed a milling reaction in real time, utilizing highly penetrating X-rays to see the rapid transformations as the mill mixed, ground and transformed simple ingredients into a complex product.

Researchers hope that their discovery will advance scientists’ understanding of processes central to the pharmaceutical, metallurgical, cement and mineral industries. Their finding could also open new opportunities in “green chemistry” and environmentally friendly chemical synthesis.

Mechanical force can be used to synthesize new chemical compounds and materials. Ball milling is becoming increasingly popular in the production of highly complex chemical structures. To create these chemical structures, steel balls are shaken with the reactants and catalysts in a rapidly vibrating jar. Researchers say that chemical transformations occur at the sites of ball collisions. Without access to real time reaction monitoring, scientists were unable to fully understand mechanochemistry.

“When we set out to study these reactions, the challenge was to observe the entire reaction without disturbing it, in particular the short-lived intermediates that appear and disappear under continuous impact in less than a minute,” says Tomislav Friščić of McGill University.

The research team looked at the mechanochemical production of the metal-organic framework ZIF-8 from the simplest and non-toxic components. The team notes that materials such as ZIF-8 are growing in popularity because of their ability to obtain large amounts of CO2. Scientists believe that they could become universally used for carbon capture and storage if manufactured cheaply and sustainably.

“The team came to the ESRF because of our high-energy X-rays capable of penetrating 3 mm thick walls of a rapidly moving reaction jar made of steel, aluminium or plastic. The X-ray beam must get inside the jar to probe the mechanochemical formation of ZIF-8, and then out again to detect the changes as they happened,” says team member Simon Kimber, a scientist at the European Synchrotron Radiation Facility.

Researchers believe that this technique could be used to examine all types of chemical reactions in a ball mill.

“That would translate into good news for the environment, for industry — and for consumers,” Friščić says.

The study’s findings are described in detail in the December 2 issue of the journal Nature Chemistry.

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