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“So I had a flaming flask in my hands…” courtesy of potassium hydride

Milkshake of Org Prep Daily this week reported on a fire in his lab from a potassium hydride reaction:

I had a rather bad fire last Friday. I was washing a large jacketed glass reaction vessel used for polymer scale-ups, after pouring the reaction mixture out, and a tiny particle of potassium hydride (from this poorly quenched reaction) that was adhering to the bottom of the reaction flask ignited just as I was giving the flask a proper acetone rinse. So I had a flaming flask in my hands + burning hands + flaming sink in front + a whole bunch of wash bottles ablaze next to me (plastic wash bottles peeing their burning solvents around…) A colleague promptly put the fire out with a mid-sized CO2 fire extinguisher before the flames spread any further. There was no damage to the lab, my fingers or the reaction mixture but it was pretty scary situation – considering how fires in organic labs can get out of control so fast.

There’s more at his post, where he includes a general heads up to the chemistry community:

Since K-alkoxides have significant reactivity advantages over Na and Li alkoxides in alkylation reactions[2], and since the easy-to-handle KH formulation in paraffin wax is now commercially available, it is likely that KH will get used increasingly more in place of NaH. Despite its innocuous appearance KH is less tame than NaH; having unreacted KH excess present in the reaction mix makes it prone to suddenly burst into flames during the workup if the reaction is not quenched with care.

Derek Lowe weighed in on the incident at In The Pipeline: “If you’re going to use KH, don’t let your guard down.”

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