Claisen condensation assumption.

[FROGGBUSTER]

In the Claisen condensation, are you assuming you're not adding enough H30+ in the final step to turn the ester into a carboxylic acid?

---

Members don't see this ad.

 

[Golfguy]

That seems like it may be a mistake frog. I believe it could be done in water. But suppose the side product could be protonated 1:1, thus leaving neutral water, so maybe it is correct (otherwise the solution would turn basic).

 

[flin5845]

It is a good question...

Since it is listed as a 2 step process, the final product of the first step is not the actual final product. Since there is a ethoxy group and an acidic hydrogen (the one between the 2 carbonyl) the ethoxy will deprot it.

The second step is reprot of that hydrogen.

My professor always told us in order to get the ester-->acid we would need an excess of H3O+.....So I guess you are right and assume there is not an excess or just 1 eq

 

[mh0000]

You form a 1,3 dicarbonyl, so any excess base will deportonate this acidic hydrogen. The acid is used to protonate this carbanion, which helps drive the equilibrium to the right. I would interpret the second step to be that only a molar equivalent of acid would be used for this reprotonation.

 

[AlbinoPolarBear]

Second step is water work-up in dilute acid.

The whole purpose of that step is to protonate any remaining negative charges on oxygen.

 

[FROGGBUSTER]

Thanks guys.

 

[Troyvdg]

Second step is water work-up in dilute acid.

The whole purpose of that step is to protonate any remaining negative charges on oxygen.

acid work up is to protinate the alpha carbon. You now have a remaining Hydrogen between two carbonyls, more acidic that what you started with. If you don't do a dilute acid workup, you'll end up with a protinated leaving group-in this case the ethanol (it deprotinates the alpha H again) and another enolate