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March 6, 2013
Safety Warning: Togni's Reagents
Posted by Derek
Some of you may have used the second Togni reagent (shown) as a trifluoromethylating agent. Well, there's a new paper in Organic Process R&D that brings word that it's an explosive hazard. A group at Novasep, in Leverkusen, Germany finds that it has a powerful exothermic decomposition, and (in addition) it's about as combustible as black powder. Sensitivity to impact and friction varied from sample to sample as well, which isn't what you want to hear, either. Their conclusion is that the reagent is "dangerously explosive and may only be transported by approval of the national competent authority." The first Togni reagent (with a dimethyl in place of the carbonyl) wasn't fully evaluated, but it may be just as bad. That one has been available from Aldrich; I imagine that this may change shortly. Too bad - these are useful reagents, but not if you have to suit up to use them safely.
Comments (10)
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1. Dave on March 6, 2013 2:55 PM writes...
Not too surprising. That trivalent Iodine can't be too happy, and that five membered ring should be trying to come apart. It might be interesting to see the decomposition products, just to determine how it wants to rearrange itself. It's hard for me to believe that it would be quite as explosive as black powder, but it may be close in terms of sensitivity (Black powder is a pain to work with!).
Dave
Permalink to Comment2. Robert on March 6, 2013 3:46 PM writes...
There's also a S-trifluoromethyl dibenzothiophenium (tetrafluoroborate?) salt that seems to be used in electrophilic trifluoromethylation papers as well. The dibenzothiophene byproduct might be too heavy to stink strongly, but I don't know.
I guess it's a natural consequence of trying to make an electrophile out of something that really doesn't want to be one, but it seems like the electrophilic trifluoromethylating reagents involve reagents roughly the size and weight of a barn door.
Permalink to Comment3. Andrew (@_byronmiller) on March 6, 2013 5:54 PM writes...
This is a newbie question: if these have been used widely, how come this is only just coming to light?
Permalink to Comment4. Anonymous on March 7, 2013 7:31 AM writes...
#3 because this is how we learn about them. They are widespread enough that people think about using them at large scale and hence perform feasibility studies. None of this matters when working with a few mg of the stuff.
Permalink to Comment5. curious on March 7, 2013 8:13 AM writes...
What is Black powder?
Permalink to Comment6. Okie Chemist on March 7, 2013 9:58 AM writes...
Curious - "Black Powder" = Gunpowder.
Permalink to Comment7. Anon on March 7, 2013 9:58 AM writes...
Black Powder is the original explosive used to make guns and cannon go boom... a mixture of mostly potassium nitrate, charcoal, and sulfur
Permalink to Comment8. Mike P on March 7, 2013 11:46 AM writes...
If these have been used widely, how come this is only just coming to light?
Black powder can be safely handled by pouring, weighing, etc. Chemists don't handle Togni's Reagent any more roughly than that.
Permalink to Comment9. Patrick Eisenberger on March 7, 2013 12:28 PM writes...
We used to refer to this method of trifluoromethylation as "fluorine chemistry for sissies", since you did not require harsh, corrosive fluorinating reagents. It seems this is no longer the case. But hey, DMP (and its precursor IBX) makes a pretty nice bang and is used routinely in organic chemistry. These things are called reagents for a reason: they are designed to be reactive.
Permalink to Comment10. Real issue? on March 10, 2013 12:14 PM writes...
The tests as described in the Organic Process R&D paper are carried out routinely in any professional process chemistry setup nowadays. Furthermore, the results are not a big surprise. The issue is not as dramatic as to become the subject of a major discussion.
Permalink to CommentObviously, these compounds need some attention when it comes to their safety on scale. But based on a detailed evaluation in a risk assessment they may be used safely with appropriate measures in place.