In this video we synthesize Ethyl Propionate by Fischer Esterification but help along the process using molecular sieves and a soxhlet extractor.

Esters are formed by reacting acids and alcohols. A byproduct of this reaction is water. Unfortunately the water present can react back with the ester formed to destroy it and create the original acid and alcohol again. To drive such reactions forward either the water or ester has to be removed.

In the case of ethyl propionate in particular. We previously only obtained 40% yield when reacting propionic acid and ethanol. All attempts to improved the yield using different quantities of reagents failed.

Water is difficult to remove from this mixture because water is higher boiling than ethanol and ethyl propionate so they should distill off first. Even worse is that water forms azeotropes with them so we'd never be able to distill just the water.

In another video we showed that molecular sieves could very effectively remove dissolved water from organic solvents. Unfortunately they are destroyed by acids.

Luckily there is a workaround. The soxhlet extractor we showed in a previous video can hold the molecular sieves and expose them to the volatiles from the boiling esterification mixture. The acids are generally not very volatile so they don't come in contact with the molecular sieves. But if the azeotropes from the esterification mixture contain water, even if just a few percent, then the molecular sieves will remove the water and return the rest of the organics to the esterification mixture. With time the continual removal of water drives the reaction forward.

In our video we mixed 80mL of propionic acid, 100mL of ethanol and 4mL of sulfuric acid. On top of an erlenmeyer flask containing our boiling mixture, we setup a 100mL capacity soxhlet extractor containing 80g of dried molecular sieves. after heating for 8 hours, the mixture was washed with 100mL water and the organic phase recovered to give 103g or 93% of very crude product. Fractional distillation may be used for additional purification.



Related videos:

The original video on making Ethyl Propionate:    • Make Ethyl Propionate by Fischer Este...  

Drying alcohol with molecular sieves:    • Drying Alcohol Using Magnesium and Mo...  

Soxhlet extractor:    • Lab Equipment: Soxhlet Extractor (Fixed)  


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