Fantastic Fischer

We are again using a very old reaction, mineral acid catalyzed Fischer Esterification, to synthesize new compounds. Last year we synthesized propyl 2-methylbenzoate, propyl 4-methylbenzoate, and propyl 4-methoxycinnamate which have not been characterized by modern spectroscopic methods. This year I replaced 4-methoxycinnamic acid with gallic acid and added 2-propanol to the list of alcohols. Isopropanol worked will as the acid despite the fact that it is not a primary alcohol which are typically favored by undergraduate Fischer Esterification experiments. Gallic acid was also a challenge due to its three phenolic hydroxyl groups. The gallic acid products were a bit sticky and did not give very clean salt-plate IR spectra. Therefore, we also did UV scans of the gallate esters. Additionally, the gallic esters did not elute from the GC column so we did an HPLC chromatogram with detection at 254nm. The esters are easy to separate away from unreacted carboxylic acid by liquid-liquid extraction with an aqueous base. It was more difficult to separate the alcohol, soluble in both aqueous and organic phases from the ester. However, with prolonged evaporation the alcohol can be eliminated from the product mixture.


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