FrankMartin - 25-10-2022 at 19:40
Hi, in the malonic ester synthesis I have read two ways of alkylating malonic ester. (ME).
For example: Alkylating malonic ester with BuBr to produce monoButyl malonic ester.
Is it best to:
1/ Mix together ME & BuBr and add the NaEthylate soln dropwise?
2/ Mix the NaEthylate soln with the ME, then add the BuBr?
Does it matter which? (Reaction conditions constant) If so what are the reasons?
Many thanks.
Dr.Bob - 26-10-2022 at 09:23
I typically add the base to the ester to form the deprotonated species, then add the alkyating group slowly into that. But much depends on the
details. If the deprotonated species is too insoluble, that can make a goo, so then maybe the first route is better. Also, if the alkylating agent
is not stable to base, route 2 is better, like for phenethyl bromide, which eliminates to form styrene if exposed to strong base. But for many
reactions, it is hard to predict the better route.
FrankMartin - 27-10-2022 at 13:08
Thank you, evidently the dropwise additon of the ethoxide might be the more generally safest way. I will test this method on a synthesis of nBuME
using ME & BuBr in the near future & report back. I have already done this reaction the usual (add BuBr last) way, so I can compare.
FrankMartin - 30-12-2022 at 14:57
Thanks, I have tried both ways for:
ME + nBuBr = nBuME + NaBr.
1/ nBuBr added dropwise to the ME/NaOEt
2/ NaOEt/EtOH added dropwise to the nBuBr/ME mix.
There was little difference in the quantity of crude product produces & a TLC of this showed similar results.
1/ 189gm, brown color
2/ 176gm no color
A reference to the Merck nBuME gave the TLC pictured, with the top spot the nBuME & the lower one the ME, so there was much unreacted ME.
I used the Vogel methods.
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Fery - 1-1-2023 at 08:55
Hi FrankMartin, this is very useful info! So the route 2 gave better purity product? Or even route 1 with brown color product after recrystallization
gave good purity too?
FrankMartin - 4-1-2023 at 12:27
Hi, I am trying to distil the products from the two reactions. I will report back.
Regards, Frank