[mpierc18]

So I know there is a phase transfer issue here which can be overcome by using glacial acetic acid, a PTC like an ammonium salt, or DMSO but why can it not be done in acetone? Tautomerization? Clueless...

[mpierc18]

For example if you wanted to add HBr(aq) or HCl(aq) to hexene, it would separate into two separate phases and you would need a PTC like an ammonium salt, glacial acetic acid or perform the rxn in DMSO.... Could one use acetone as a solvent to forego the PTC? If not, then why? I've posted a similar question in the organic chemistry section but haven't received any responses. I don't think it's tautomerization and I'm pretty sure a haloform rxn wouldn't take place because one would need basic conditions and the halogen in its X2 form instead of an acid... Also, since there is no peroxide present I don't think there would be a risk of forming an explosive. Any thoughts?

[Archer]

Are there any reactions that may occur if you mix acetone and a strong acid?

[Dan]

Tautomerization?

Yes, I'd expect that to cause problems. Do you have any ideas about what might happen when you mix acetone and HBr?

[mpierc18]

So... Questions within questions... what kind of problems?

[Archer]

We are trying to get you to come up with the answer as you almost certainly know it.

Draw the tautomers of acetone and draw what happens to acetone when there is a lot of H⁺ around.

Then look at the two of them and think about core carbonyl chemistry.

[mpierc18]

But would that interfere with the HX addition? or just produce a by product?

[mpierc18]

Also, it would tautomerize but then what? X- is a poor nucleophile and OH- is a bad leaving group so it seems to me that the reaction would stop there (at tautomerization).

[Archer]

Also, it would tautomerize but then what? X- is a poor nucleophile and OH- is a bad leaving group so it seems to me that the reaction would stop there (at tautomerization).

Look up Aldol reactions then apply how good a leaving group H₂O is to the product of acetone in strong acid.

[mpierc18]

So would aldol condensation affect the addition of HX??

[Archer]

So would aldol condensation affect the addition of HX??

You will end up turning your solvent into phorone, a low melting solid which is not water soluble

[orgopete]

I see this question/problem differently. The addition in question is an uphill reaction in that an alkene is a very weak base and bromide or water are stronger bases. A reaction with the alkene is a kinetic event that occurs in the presence of a greater thermodynamic equilibrium. Adding another base like acetone can shift the equilibrium or be a reactive reagent.

I suggest looking up the pKa's of the conjugate acids. I don't recall the value of acetone, but it will be protonated before the alkene. Protonating acetone will not automatically result in an aldol condensation, there are many more steps that must occur. However, a protonated ketone can react with an alkene. Depending on the concentrations, reaction rates, etc, I think this is likely to be the reaction you will find. However, the reaction will not stop there. Addition to the alkene will generate a stronger and in the case of acetone, a more easily eliminated base.

I think this reaction will give a mess. It may include an acid catalyzed aldol product(s). Without the alkene, clean and high yield acid catalyzed aldol reaction are difficult to find. That is virtually easily predicted if you consider the concentrations of reactants likely to be present. With an alkene present, this prediction is even more difficult. Look up Prins reaction.

[mpierc18]

That helps a lot orgopete! Thx.