[OrganicH2O]

I already know the rule of thumb that you can't make a tertiary ester with with RCO2H + tert-butanol + acid catalyst. And I already know the  basic explanation that the reaction works poorly because the tertiary alcohol is prone to E1 elimination creating isobutene.

I also know that the reaction does work with RCO2H + excess isobutene gas/acid catalyst.

So that's all easy enough to remember, but it just doesn't quite make sense to me from a kinetic and/or thermodynamic perspective. If the reaction fails with tert-butanol, why does it work with isobutene? Afterall, tert-butanol is eliminating to literally make isobutene. Why not just add excess tert-butanol as the solvent?

One possible explanation I can think of is that the tert-butyl ester is less stable than other types of esters, and so one equivalent of water will simply hydrolyze it at equilbrium. Maybe adding one equivalent of isobutene is just a way to run the reaction with zero water molecules present? And it's not practical to run the reaction in a way where water is being removed to avoid this.

[Babcock_Hall]

At what temperature does one ordinarily perform a Fischer esterification?

[OrganicH2O]

Most Fischer esterifications are done at high temp because otherwise it's slow. So that makes elimination of the alcohol more likely.

But the hypothetical reaction of tert-butanol + RCO2H would occur via a different mechanism than typical Fischer esterification, where the tertiary alcohol forms a carbocation that is attacked by the carboxylic acid. This would make it similar to a related reaction that does work: excess primary alcohol + Tert-butanol + acid catalyst --> tert-butyl ether.

That suggests that a Fischer style process for RCO2H + tert-butanol would work if you used excess RCO2H, but probably in lab synthesis the RCO2H is likely complicated/expensive and this is undesirable.

[hollytara]

Take a look at this paper - see what happens when you heat a t-butyl ester in the presence of acid...

Publication:
Proc. SPIE Vol. 1086, p. 11, Advances in Resist Technology and Processing VI, Elsa Reichmanis; Ed.
Pub Date: August 1989
DOI: 10.1117/12.953013