Two 1mol reduction reactions of the following compound 10 were carried out. The reaction operation was very standard, which was called argon flow. The whole reaction process was maintained at about 5 degrees Celsius, and the reaction was monitored after several hours of stirring. One of the 8L reactors was quenched with ice methanol. As soon as the first drop of methanol was added, an orange flame immediately appeared in the reactor and exploded. The reactor was destroyed, the glass baffle broke, and a researcher was seriously injured by debris and flames
The reduction mechanism of this reaction system is as follows: alumane is an active species generated in situ. There are many studies on this. According to the literature reports, pure alumane is stable under the condition of 100 degrees Celsius. However, its stable temperature drops significantly in the presence of a catalyst. By reviewing the literature, researchers found that polyfluoroorganoaluminum compounds or Grignard reagents are very easy to explode. These explosions can be caused by heat or a simple squeeze of a spoon
In addition, in the past few decades, there have been two reports of explosions in the reduction of polyfluorinated organic compounds involving LiAlH4, both occurring during the post-treatment quenching phase. The researchers hypothesized that the explosion was probably directly related to polyfluorinated compounds. They ran this hypothesis through a series of tests. The solid complex formed by the reduction of compound 10 is likely to explode at temperatures below 60 degrees by a simple heating test (protected by a baffle). However, the solid complex formed by the initial raw materials corresponding to products 2 and 9 only becomes darker under the condition of 60 degrees, and the combustion will occur when it reaches about 90-100 degrees. Based on this, the authors believe that polyfluorinated feedstocks containing trifluoromethyl are more likely to burn and explode.
Just because it’s a dangerous reaction doesn’t mean we shouldn’t do it. Other reduction systems, NaBH4/CoCl2, NaBH4/NiCl2 and LiAlH4, were tried for this substrate, but they all failed to give good results and produced byproducts. The borane reaction gives good results, but the reagent is expensive and difficult to scale up safely. Finally, the author used Raney Ni/NH3/MeOH/H2 system to solve the problem successfully
For sensitive unknown reactions, it is best to do DSC, TGA and other tests before amplification, but it is difficult to complete these tests in conventional laboratories. Even if the reaction is fine on a small scale, there is no guarantee that scaling up will be safe. Therefore, we must take good personal protection before the experiment.