[RkRs21]

Hi all!

In my most recent lab assignment (bachelor's student) we were set to make 2-octanone via an Acetoacetic ester. With the mechanism figured out and written down, I went to work. The plan would be as follows:

• Dissolve sodium in ethanol to deprotonate the C-α position between the ketones.
• Add 1-bromopentane to make the main chain carbon-carbon link
• Hydrolyse the ester in 4M NaOH to 2-acetylheptanoic acid (and ethanol)
• Lastly decarboxylate in acidic conditions

Everything seemed to go as planned, right up until I checked a layer labelled as 'waste' after the hydrolysis step (I separated off what I presumed to be unreacted material). At the advice of my tutor, I made an infrared absorption spectrum of the waste material. It so turns out that it was a very close match to the spectrum of 2-octanone. This arises a crucial question I haven't been able to answer after asking around on the lab floor or doing thorough searches on the internet:

Is it possible to decarboxylate under (strong) basic conditions?

From what I found online the main problem would be that the acid will be deprotonated, making it impossible for the concerted mechanism to work. (Going off the image below).

Thanks a lot!

[phth]

Yes,

If you dissolved the base too quickly there could be enough heat to decarboxylate the anion. This mechanism is known as the kraptcho decarboxylation but with sodium not lithium: https://en.wikipedia.org/wiki/Krapcho_decarboxylation

[rolnor]

It requires 150° so I think not.

[rolnor]

Also, you need the ester+halide ion, not the carboxylate so I think not.