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Author: Fernando Gomoron-Bell2021-12-10T09:30:00+00:00
Researchers at Hokkaido University in Japan have discovered a new method of using mechanochemistry to prepare Grignard reagents-and these reagents will not be destroyed by air. "It's easier and faster," said Deborah Crawford of the University of Bradford, UK, who was not involved in the study. "If I need Grignard reagent, I will use [this] method now."
Source: © Rina Takahashi et al. 2021
Grignard reagents are organomagnesium compounds and are widely used in organic synthesis because of their versatility to create new carbon-carbon bonds. However, their preparation usually requires temperature control, drying of solvents, and protection from air and moisture by inert air methods (such as Schlenk lines). "This is the first example of the preparation of Grignard reagents under ambient conditions... This is very remarkable," Crawford said.
The secret weapon of the Japanese team is mechanochemistry-using a ball mill to grind reagents together. Although other researchers have studied the reactivity of organic halides and magnesium under these conditions, the team went further. “We found that [adding] a small amount of [tetrahydrofuran] effectively promoted the formation of Grignard reagent,” explained Koji Kubota, who co-led the research. 'The setup is very simple: add stainless steel balls, organic halide, magnesium and tetrahydrofuran [all] to the grinding tank. Then you just need to press start.
The whole process is carried out in air. In addition, the prepared Grignard reagent can be used for subsequent reactions without additional purification. Crawford said the researchers demonstrated the excellent response range of the reagent. The magnesium compounds made by mechanochemistry can be used for carbonyl addition, cross-coupling reactions and more reactions. "Some of the transformations [they] proved are difficult for traditional [chemical synthesis]," she said. Eventually, these Grignards will indeed deteriorate in the air. However, this is not a problem, Crawford believes, because chemists often use Grignard reagents immediately.
In addition to the practical advantages, Kubota said this method is more environmentally friendly-reducing the need for special preventive measures "is very beneficial from an environmental and economic point of view," he said. Evelina Colacino, an expert in mechanochemistry at the University of Montpellier, France, attaches great importance to the "simplicity...and practicality of the agreement". She also commented on how mechanochemistry broadens the scope of traditional chemistry. "It provides access to new molecules... it makes it possible to make compounds that are not available in solvent-based processes," she added.
The new mechanochemical synthesis is optimized to prepare 1g Grignard reagent. However, before considering mass production, the team plans to study the long-term stability of these compounds—in addition to oxygen and moisture, carbon dioxide can destroy them, Colacino explained.
Crawford wondered whether exploring twin-screw extrusion-a technique for large-scale mechanochemical preparation-might accelerate the scale-up process. "We can [then] see the largest economy and sustainable savings," she said. Kubota confirmed that their team is currently investigating stability issues and the potential for commercialization of Kuma Grignard products.
R Takahashi et al., Nat. Commun., 2021, 12, 6691 (DOI: 10.1038/s41467-021-26962-w)
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