The Naked Scientists Forum
Non Life Sciences
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18/05/2006 19:36:49 »
I'm looking for a solvent for an SN2 substitution reaction that won't promote an E2 elimination reaction at the same time.
Right now I'm using tiethylamine as a base but its also acting as a nucleophile slowing the desired reaction.
The solvent of the reaction is ethanol which also slows the reaction because it is a polar protic solvent.
DMF and DMSO are polar aprotic and are used often in SN2
Does anyone know the pH of either of these solvents pure??
Are they basic or acidic.
(Trying to kill two birds with one stone)
Reply #1 on:
25/05/2006 20:32:36 »
If the solvents are pure, there is no pH, since pH refers to the H+ concentration in water.
Both can act as Lewis bases, but they're not very good Bronsted bases.
I'm curious as to what the purpose of the NEt3 is, if not for a nucleophile or to promote elimination.
Reply #2 on:
26/05/2006 03:51:45 »
The NEt3 is acting as a base.
The reaction is ethyl-glycinate adding to 2-bromo-diethylphosphonate
It is an SN2 reaction where the N-terminus of the glycinate is the nucleophile. Br is the leaving group.
So the reaction conditions must be at a pH higher than the pKa of glycinate so that the nitrogen is not completely hydrolyzed. It must have a lone pair to act as a nucleophile.