[Honclbrif]

I've got an old bottle of BF₃-OEt₂ that's turning brownish. Is it worth distilling it, or should i just get a new one?

[Dan]

I've never attempted to distill it because it's really cheap.

[nox]

Get a new one, OR if you're not running something terribly important, go ahead and do a small scale reaction and see how it works. I've used yellow-brown BF₃ from a Sigma bottle that had a terribly corroded SureSeal cap and the reaction still went fine. Granted it was a rather trivial FC cyclization so YMMD.

[Åke]

Depends what you want to do. I've been able to get away with the dark brown boron trifluoride etherate when making borane (from NaBH₄). If your substrate is a very valuable one then I think it's better to buy a new bottle of BF₃·O(Et)₂ especially as it is inexpensive.

[g-bones]

like these guys have said, if it isn't terribly important material you are using, just use an excess of BF3.  If ordering is a pain and you don't have the time to wait for your new bottle to arrive AND the reaction is sensitive to small impurities, give it the old distillation, its not horribly hard, but its a bit of a pain.