Take care with triethoxysilane

A hat tip to our colleague and The Haystack blogger Carmen Drahl for catching this addition/correction relating to a paper from Matthias Beller‘s lab published earlier this year in the Journal of the American Chemical Society:

Our Communication did not emphasize important safety considerations in the reported reactions.

Buchwald and co-workers previously studied the Ti-catalyzed reduction of amides to amines or enamines.(1) Additionally, in 1992, Berk and Buchwald reported the combination of 5 mol % Ti(O-i-Pr)4 with 2.5−3.0 equiv of (EtO)3SiH for the reduction of esters to silyl ethers at 40−55 °C.(2) An attempt to use this procedure for the reduction of a methyl ester (90 mmol) with triethoxysilane (313 mmol) resulted in the formation of an extremely pyrophoric gas (possibly SiH4), leading to several fires and an explosion.(3)

During our studies on the reduction of amides, we used triethoxysilane without incident, although the Material Safety Data Sheet indicates that this chemical is a corrosive and flammable liquid. Due to the previously reported hazards, we advise that methyldiethoxysilane be used instead of triethoxysilane for the large-scale (>1 g) reduction of amides. As shown in the Supporting Information of our Communication, methyldiethoxysilane and other organosilanes can also be used for the reduction of amides at slightly higher temperature, e.g. 60 °C. We thank Professor Buchwald for pointing out these latent safety problems with triethoxysilane.

Reference 3 is to Buchwald‘s safety letter to C&EN, Silane disproportionation results in spontaneous ignition.

Kudos to Buchwald and Beller for following up on this.

Author: Jyllian Kemsley

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  1. I believe purchased triethoxysilane usually has residual SiCl – up to 5 mole% HSiCl(OEt)2. The residual acid stabilizes it towards redistribution to Si(OEt)4 + SiH4. In one case, I neutralizied a small ammount using if I remember correctly CaCO3 in a borosilicate glass vial. After neutralition, I distilled the material and stored in the same type of vial. After several weeks, it detonated when I opened it.

    Triethoxysilane also “Eye contact can result in corneal
    damage or blindness. (https://www.spectrumchemical.com/MSDS/TCI-T1040.pdf)


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