Chemical Forums

Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: reflux on December 04, 2009, 09:23:36 AM

Title: Titration of TBAF
Post by: reflux on December 04, 2009, 09:23:36 AM
Is there any method out there to determine the concentration of the fluoride anion in a TBAF/THF solution or other fluoride sources?  The quality of our TBAF (1M in THF from Aldrich) tends to drop off irregularly, it would be helpful to know the actual concentration of fluoride in the bottle.
Title: Re: Titration of TBAF
Post by: stewie griffin on December 04, 2009, 10:01:46 AM
I actually just posted on your other post about TBAF  :)
So are you waiting for the solids to fully redissolve after you pull the bottle out of the fridge? If not, then you are using a solution of lower molarity.
We also get our TBAF from Aldrich and have not had any problems with it. After extended periods the reagent tends to not work as well and we'll get a new bottle... but it certainly isn't problematic to start with (at least for our purposes anyway).
Title: Re: Titration of TBAF
Post by: reflux on December 04, 2009, 12:11:05 PM
Thanks for the posts!  I agree, the solids crashing out in the fridge are mostly the TBAF salt.  I don't cool it below zero though.  My theory is that if you freeze out the water then the TBAF decomposes (it is actually required to stabilize the TBAF... I have a reference if anyone wants it).  When I set it on my bench to warm up for ~1 hour the solids never fully redissolve so I'm sure we're working with less than 1M concentration.  And using excess kills my reaction.

So I'd really like to find a way to titrate for the F- concentration in an organic solvent.  I was thinking of bis-silylating something that when exposed to 2 eq of F- would generate a dianion (similar to titrating your LDA or nBuLi).  But the water in the TBAF would complicate the equilibrium.
Title: Re: Titration of TBAF
Post by: nj_bartel on December 04, 2009, 12:26:19 PM
Is the solution conducting?  If there's a THF soluble calcium salt, you could do it potentiometrically maybe?