New in Grignards

19 January 2020 - Industrial chemistry

Researchers from the Fraunhofer IMM institute in Germany have devised a metal reactor for the continuous delivery of Grignard reagents as reported in OPR&D (DOI). The lab-scale synthesis of these reagents is always a challenge let alone their use in industry. The authors note the dependence on the type of halide, the type of activation (classic reagent is iodine) and the exothermicity of the reaction once the organomagnesium compound has formed. The novel reactor was built using 3D selective laser melting, not an entirely surprising choice since the technique was invented by Fraunhofer in 1995. The article or the patent do not disclose what metal was selected (secret, obvious, should read more carefully or should have been mentioned).

At the heart of the device is a reactor filled with magnesium turnings. Next are an inlet for halide and a outlet for product, 4 temperature readers and a ATR-IR spectrometer. The magnesium turnings are activated in a mechanical grinding process via vibration, rubbing the turnings together removed the inactive outer layers. Magnesium is also present in a large up to 30-fold excess with respect to the halide. All reagents and solvents are used as is from the supplier. Reported yields are 90% and up with molar range 1 -2 mole/L and residence time up to 30 minutes.