[pallidol]

Hi there. I need some recommendation for my work.
 I performed dieckmann cyclisation using sodium metal in dried methanol then refluxed for two hours. The work-up procedure is using toluene and water and the aqueous phase was acidified with 1M HCl. No precipiatte appear thus i continue with extraction  using ethyl acetate and dried under pressure. The product is expected to have a methyl ester substitution but unfortunately from NMR spectrum it has cleavaged. How to performed the work-up procedure in a right way in order to avoid the cleavage of the methyl ester group.

The reaction scheme as attached. Thank you beforehand.

[pgk]

Two different things or their simultaneous combination might have happen:
Either, methanol wasn’t “super dry” and thus, methanolic NaOH was formed that hydrolyzes the methyl ester to free carboxylic group, which is then thermally cleaved during the reaction process.
Or, the concentrated HCl 1N (which is rather concentrated) exothermically neutralized MeONa, during the extraction procedure. The so liberated heat accelerated ester hydrolysis and the further accompanying decarboxylation at room temperature, due to the α-,α’- neighboring with two carbonyl groups.
Thus:
1). You prepare “super dry” methanol, according the protocol that is described in the “Vogel’s Textbook of Practical Organic Chemistry” (treatment with Mg flakes, followed by distillation) and you keep over molecular sieves 4 Å (preheated at 110oC, overnight), in cupped bottle that is sealed with Teflon tape.
2). You extract with HCl 0.1N or saturated NH4Cl, aqueous solution that are preliminary cooled in the refrigerator, at ≈ 4-5oC.
By the way, did you observe any bubble formation, more than usual when adding Na to MeOH and/or any warming of the aqueous phase during extractions?

[wildfyr]

The best way Ive seen to dry methanol is to bake the everloving hell out of some 3A sieves then use them at 10-20 wt% in methanol in a sealed container for 3 days. Gets you down to 10-20 ppm water. http://ccc.chem.pitt.edu/wipf/Web/Solvent_Drying.pdf

[pgk]

Where the problem is!
1). If using elementary alkalies or organometallic reagents and working in high dilution, 10-20 ppm water might be too much and might alter the overall yield and the obtained results.
2). Molecular sieves are zeolites with a pore size = 3-4 Å, which is about the size of water molecule (≈ 3 Å) and thus, they capture by absorption process, the contained water that is in a liquid but not in a gaseous state.  However, absorption is a physical process that is reversible, depending on the physical conditions. In other words, molecular sieves may liberate the captured water back, due to temperature and pressure variations.
Therefore, molecular sieves are suitable for capturing traces of water and not appropriate as a heavy-duty dehydration medium.
3). Using molecular sieves at 10-20 % w/w for methanol dehydration, is highly costly and beyond any further consideration.

[pgk]

Another possible source of humidity that came today in my mind, is using glassware that is not preliminary washed with acetone and dried in the oven, or used long after that drying procedure.