[rucik5]

Hi, I was wondering if someone could help me with this one.
Dimethyl malonate shows 2 singlets on the NMR, 2:6 ratio.

A known amount of DMM is added to methanol, along with 1 eq of NaOH. The contents are shaken briefly, (rotavaped and dissolved in D2O or CDCl3 for nmr) and sampled. GC shows no DMM present, and no other products are detected. On the NMR there is no DMM and a new singlet appears.
After acidifying the sample (formic acid in MeOH), the GC shows DMM again (let's say 90% is back).

First I thought maybe it's a tautomerism, or the hydrolysis and formation of the disodium salt but that probably requires some time and temperature. And, it wouldn't give DMM but the acid back. I can't believe it would re-esterify so fast. Or will it? Could it be some sort of a complex? Seems like a really simple chemistry issue. Thanks.

salt?

[Dan]

I think you're on the right lines with your salt idea, this is why you see nothing by GC, but you have the wrong salt. 1 eq NaOH is not enough to form the disodium salt. Hydrolysis is a logical idea, but consider:

NaOH + MeOH <---> NaOMe + water

If methanol is the solvent, the equilibrium will be far to the right  - rapid hydrolysis seems unlikely. How acidic is DMM vs MeOH?

Now, the only problem with what I'm getting at is the NMR - I'd expect 2 peaks for the new product, so perhaps I'm wrong.... then again, if the solvent is D₂O this could be explained.