I am attempting to convert the salicylaldehyde into the correspondent dimethyl acetal using the following procedure. I dissolve it in MeOH in presence of triethyl orthoformate and decaborane as catalyst.
After 10 min the reaction is completed and the workup is done by diluting the mixture with NaHCO3 5% or saturated solution, and extraction in DCM or ethyl acetate. The organic layer is then washed with either brine, or simply water, anhydrified with MgSO4 and concentrated under reduced pressure. Whatever I do, after the work up, the TLC shows partial conversion of the product into the starting material? I thought it could be a result of the instability of the product to the weak acidity of the silica on the TLC, so that it back hydrolyses to aldehyde on the TLC plate, but if so, this should happen even before. When monitoring the extent of the reaction, this is not the case.
Thank you for your interest
Thank you Shaban Ahmed, but here the question was more addressed to the stability of such derivatives, or meant to get any hint if the work up described does not apply as inappropriate for the stability of the product.... using decaborane the dimethyl-acetalization goes to completeness within minutes
I would suggest to use Na2SO4 as the drying agent rather than MgSO4, which is slightly acidic and not suited for acid-sensitive compounds (such as your acetal certainly is). See for instance: http://www.scripps.edu/shenvi/Education_files/Drying%20Solvents%20handout.pdf
Thank you Stefan Bienz, I forgot to mention a detail in the formulation of the question.....before adding MgSO4, i keep the pH basic with TEA which then goes away under reduced pressure.....but probably this doesnt help...still thank you very much....this could really be the reason...
Try to remove the solvent with vacuum alone, works well if you have a dry ice condenser on a rotary evaporator.
There is a small chance that the product you are after has some thermal instability if you still have the weakly acidic free phenol from salicylaldehyde. I would also recommend using Na2SO4, particularly given the ability for your system to chelate via a 6 membered ring.
Article A Simple and Versatile Method for the Formation of Acetals/K...
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