2-bromo-N-methylpyrrole and molecular sieves

A student brought ~5 mL of homemade 2-bromo-N-methylpyrrole, an orange liquid, into a glovebox and placed the neat liquid over activated molecular sieves (MS). The student transferred the liquid into a 20 mL scintillation vial, added some 4Å MS to the vial and capped the vial. While the student was holding the vial, they noticed the MS were gradually turning black and some white fume was emanating from the liquid. The student held the vial closer to the face panel to see the change clearly. Suddenly, the vial exploded and the face panel of the glovebox was cracked. No one was hurt in the explosion. 2-Bromo-N-methylpyrrole is known to be unstable under acidic conditions, including being treated with silica gel (SiO 2 ). The decomposition of 2-bromo-N-methylpyrrole is exothermic and usually forms intractable black mass and HBr gas (white). The reason for the explosion might be that 2-Bromo-N-methylpyrrole decomposes quickly under activated molecular sieve, which has a linear formula of Na 12 [(AlO 2 ) 12 (SiO 2 ) 12 ] and high surface area for fast reaction. The 2-bromo-N-methylpyrrole and MS should not be mixed. In the future, the compound will be dried only using neutral or basic drying agent such as magnesium sulfate, and if possible will not be treated with drying agents that can facilitate decomposition.