Thursday, February 05, 2009

Evil Molecules Part 1 - Explosive Azides, Diazidomethane

Say hello to diazidomethane. Is it time for a change of underwear yet? I work with azides on a daily basis and I even determine the melting point of my azides. My azides are nice a stable because they all adhere to the 6 heavy atoms (carbon or heavier) per azido-group rule of thumb. However, if you stray from the 6 heavy atom path you are looking for trouble and if you decide to do 1/2 a carbon per azide as we have in this case you will be looking for a new chemistry department.
In this really interesting paper from Alcon Research Ltd. they unintentionally made a fair bit of diazidomethane when performing the synthetic sequence shown in the scheme below. To remove residual dichloromethan after the first step the chemists at Alcon redissolved the crude product in DMF and concentrated it to dryness. To my (and theirs I'm sure) surprise this doesn't remove all dichloromethane despite a huge difference in boiling point. After performing the second step, they worked the reaction up and concentrated it on a rotary evaporator.
 This is what they observed when they came back the next morning:
“... it was noted that about 30 mL of a twophase liquid had collected in the glass crosspiece at the bottom of the condenser assembly.
When they attempted draining the stuff it decided to go nuts. All I’ll say is that nobody died but you’ll have to dig the paper out yourself if you want the full story.
Remember, halogenated solvents (dichoromethan, chloroform, 1,2-dichloroethane...) and azide ions are bad news. Don’t do it!