[scienceguy]

Hi there,

I was investigating tetrahydrofuran as a solvent that I was planning on mixing with an acid. According to Reichardt (2005) p. 107, tetrahydrofuran undergoes tautomerism to an enol. Would this cause tetrahydrofuran to break down say in the presence of an acid? I was just wondering because I would need the tetrahydrofuran to remain intact as a solvent.

Reference

Reichardt, C. Solvents and solvent effects in organic chemistry, 3rd ed. 2005. Wiley.

[Hybrid]

it may be protonated but then it will break not tautomerize to enol

[MissPhosgene]

They are talking about solvent effects on tautomerization of ethyl acetoacetate, acetylacetone, and dimethylcyclohexane 1,3-dione. It's in the heading above the table. THF is one of the solvents Keq was found in.

[scienceguy]

Thanks!

[MissPhosgene]

No problem. It took me a minute to read the table because the formatting is sort of unclear.

[scienceguy]

So what about breaking the ring? If the oxygen on THF gets protonated, will electrons from a carbon-oxygen bond get drawn to the oxygen to become a lone pair on the oxygen, breaking the ring?

[MissPhosgene]

Well, you can cleave ethers under acidic conditions, but it will happen in an Sn2 fashion. There is another very recent thread on this topic.

[scienceguy]

Thanks again. Also, I found the other thread on this topic. Is Sn2 less favored if the ether is cyclic?

The acid I was going to mix with THF is formic acid. Would the base of formic acid be sufficient to cause this Sn2 reaction, breaking the ring?

[nj_bartel]

Probably not, given that the attacking species would be the formate ion (resonance and whatnot, crappy nucleophile).