Volkswagen alkali can decompose certain solvents, which may cause explosions

A recent report has drawn the attention of chemists to a long-standing but often forgotten hazard in chemistry. When sodium hydride (NaH) is used together with some solvents, it will generate heat and gas unexpectedly, leading to uncontrolled reaction or even explosion.

Synthetic chemists often use sodium hydride to extract protons from molecules. But to combine this ionic base with greasy organic molecules, chemists usually have to use the so-called Polar aprotic solvent, such as dimethyl sulfoxide (DMSO), di N-Methylformamide (DMF) or Dimethylacetamide (DMAc).

Yang Qiang, a chemist at Corteva Agriscence, said that reports of sodium hydride in these solvents potentially causing explosions can be traced back more than 50 years. Yang Qiang is the person in charge of the report. However, he said that every year chemists publish papers describing the use of these unsafe combinations. Yang's team reported that between 2014 and 2018, Organic Express published 38-62 papers/year, Organic Chemistry Journal published 28-46 papers/year, and Medicinal chemistry Journal published 67-94 papers/year.

Suzanne Blum, a chemist at the University of California, Irvine, said, "The most striking feature of this paper is that the author's data compilation shows that a large number of recent papers continue to use these dangerous reagent combinations

Yang and colleagues also studied the chemical substances that make these combinations unsafe. Yang said that the free radical reaction between alkali and solvent can produce gases, including dimethyl sulfide and ethylene, when sodium hydride is added to DMSO.

People should be aware of this safety hazard, "Yang said. Throughout my entire industrial career, I have not yet used these combinations, "he pointed out. Although no combination can be used as a universally applicable substitute, there are also some substitutes that can achieve the same chemical reaction. Tetrahydrofuran can be used as a solvent for sodium hydride and as a substitute for bases such as alkoxides and hydroxides. But scientists also need to understand the stability of these bases and solvents, "Yang said.

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Blum added, "As a community, our future job is to incorporate centralized hazard training into our graduate courses to make identifying hazards easier." For example, she said, papers using these conditions can display hazard information when readers click on online articles.