FrankMartin - 18-6-2010 at 17:35
Am trying the synthesis of nBuMalonicEster by the PTC route.
I am using the following stoic.:
DEM + nBuBr + 0.5(K2CO3) = DnBuM + KBr + 0.5CO2 + 0.5H2O.
As a solvent I am using Acetonitrile, as a catalyst I am using 10%TBAF, and I am trying to track the reaction (under reflux) by the evolution of CO2
which I collect in a water trap.
The reaction mix is stirred at approx 200rpm.
The quantities I am using dictate a theoretical evolution of approx 5 litres of CO2 (STP).
As always the reaction goes to about 25% and then stops. Why is this? Has anyone some experience in this difficult reaction?
Desperate.
Frank
Nicodem - 19-6-2010 at 07:46
Please open unanswerable, referenceless or lazy threads only in the Beginnings section where I'm moving this. How is anybody to know what the problem
is when you did not add the original reference for the procedure? Do you expect anybody to be able reading your mind? Besides, if you want anybody to
understand what you talk about, use chemical nomenclature instead of incomprehensible acronyms that only have a meaning to yourself. While most
organic synthetics and close to none of the other chemists will know what shorthands like Bu or TBAF stand for, the meaning of things like "DEM" or
"DnBuM" can only be found via guesswork (and we don't like to do guesswork!).
DJF90 - 19-6-2010 at 11:10
Use sodium ethoxide as the base, and ethanol as the solvent; yields approach 80% if the ethanol is dry. I am unfamiliar with the PTC method, so it
would have been nice if you could post a reference/paper regarding it. We can only help you as much as you help yourself.
Arrhenius - 21-6-2010 at 00:27
What TBAF are you using? TBAF solution? You need a better PTC, and the reaction needs to be anhydrous. Try tetra-n-butyl ammonium bromide or sulfate
instead. TBAF is not typically used as a phase transfer catalyst, and is sold as a hydrate even in solution.
Phase-transfer catalyzed alkylation of malonates and acetoacetates for those interested - they're using 18-C-6.