Sciencemadness Discussion Board

A theoretical question

Pumukli - 28-8-2023 at 09:30

I'm curious about the experts' opinion on the following:

What are the odds that I could successfully decarboxylate a particular beta-keto-ethylester and turn it into a ketone IF the original preparation in OrgSynth says that this compound requires a "pressure proof container and heating the ketoester and water mixture upto 180-190 Celsius" BUT I'd "cut the corner" and omit the pressure wessel and substitute the water with something with higher bp instead? Say propylene-glycol or glycerol or something similar protic polar solvent for the reaction?

Before I'd sacrifice (in vain) my precious little "precursor" - although it is nothing "druggy" as far as I know :) I'd like to hear about my odds!

AvBaeyer - 28-8-2023 at 15:24

If as you have written that it is decarboxylation of a beta-keto ESTER, then the role of water is critical. At high temperature and pressure, the water will convert the ester to the acid which is the actual species undergoing decarboxylation. If you change the medium to an alcoholic type of solvent as you suggest, then you might get an ester exchange, but the beta-keto acid would not be formed. Thus, no decarboxylation.

Some years ago there were several publications which showed ester hydrolysis in hot DMF or DMSO containing NaCl. There was some later controversy regarding the actual mechanism of the reaction.

Hope this helps,


Pumukli - 28-8-2023 at 20:19

Thanks! (And silly me, as I forgot that the first step was hydrolysis, then came the decarboxilation...)

Might I get away with plain water, with looong boiling at normal pressure? The reaction in the pressure vessel was finished in 10-15 minutes.

clearly_not_atara - 29-8-2023 at 02:59

If 1-phenylethanol is available, you could transesterify to this ester, then with heat and moderate acid catalyst you should see elimination of styrene with formation of the acid. There are probably a few other such alcohols as well — t-butanol is one of them but it might be hard to achieve a transesterification with t-butanol. I think that menthol might also do it.

EDIT: oh, nitpick, this is a "practical" question, not a "theoretical" question

[Edited on 29-8-2023 by clearly_not_atara]

Pumukli - 29-8-2023 at 11:36

Thanks for the idea of styrene elimination. It might be an interesting route - if I had the phenylethanol. :)

But I started thinking about simply refluxing the ester in water. In my mind I envision some sort of auto-catalytic process (at least in the beginning) where water causes some hydrolysis and then the free COOH (weak acid, but stronger than water in itself) accelerates the break down of other ester moieties. Unfortunately the other "side product", ethanol, would lower the temperature in the system by its lower boiling point... Nevertheless, this is "just another" decarboxylation and as such lends itself to monitoring by catching the CO2 and measuring its volume over time... If I could get rid of that annoyance ethanol... (Since the process also involves ethanol and distillation the thing starts to dangerously resemble to moonshine making - and if anything that is a hardcore practical question, yes!) :D

[Edited on 29-8-2023 by Pumukli]

Pumukli - 30-8-2023 at 11:33

As a more serious side note: Krapcho decarbethoxylation (or something like that) what clearly_not_atara were hinting about.
I checked the literature and it seems that my chances were fairly good if I chose this route. DMSO and water that is required, alkaline-chlorides can be omitted with my particular substrate.
Thanks for the hint! I learned something interesting again.

Attachment: decarbethoxylationdmsoh2o_2.pdf (1.2MB)
This file has been downloaded 131 times

Mateo_swe - 13-9-2023 at 06:24

Cant you just use one of those hydrothermal reactor vessels or a DIY alternative?
They are made for this kind of stuff and although somewhat expensive its not that bad if youre not going for a big one.
They are basicly just thick stainless steel containers.