I recently purchased 3 bottles of dimethyl acetylenedicarboxylate from Sigma-Aldrich and decided to check the purity of the product using TLC. I found out that the chromatogram actually showed 2 spots, Rf 0.1 and 0.8. I believe the bottom spot is due to the decomposed product since it's the minor compound of the mixture. Any idea what this could be?
Ask for information in analysis service of Sigma-Aldrich. Bottle with your reagent has a lot number with which you can get from the site of the company certificate with the name of the analyst.
Hi! The lower Rf spot may be a trace impurity of acid from uncompleted esterification or ester hydrolysis. Some acetylenes are on market at ~95% purity.
I agree with Americo. If it has been done on regular silica TLC using reasonable rather non-polar system (PET/EtOAc let´s say..), result shows that not-so-polar ester goes ahead faster (compared to free acids that are pretty polar and stay in the beginning..)
However it´s still a bit strange that rather expensive Aldrich deals with simple and easy to purify compounds that are contaminated (mild basic wash should get rid of free acids).
But without quantitative analysis Aldrich shouldn´t be accused. GC-MS (quality), GC-FID or HPLC (quantity) should tell you more.
How did you develop the TLC anyway?
I faced same problem. I gave the lover spot of dmad which is excellent solid to nmr but i did not understand what that is.
it can be 2+2+2addition product; Benzenehexacarboxylic Acid Hexamethyl Ester
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