Dear researchers,
I am currently using ethyl acetate as an extraction solvent during the workup of my lipase-catalyzed reaction. In this DSP: ethyl acetate is used first, for liquid-solid extraction then for a liquid-liquid one (in which the organic phase=EtAc is being washed from the unreacted water-soluble substrate). Thereafter the organic phase is chemically dried over MgSO4 and evaporated (rotary evaporator), the dry residue is my end product (sugar ester).
One of my goal is to continuously recover and re-use the ethyl acetate, however, I could not miss that over the cycles/batches, a strong smell of acetic acid emanates from my solvent canister and if I dry evaporate the pure, used, solvent a liquid residue remains with a smell that cannot be confused... acetic acid.
Is there a way to conserve the integrity of my ethyl acetate? Or find a way to adsorb/segregate the acetic acid at least?
My lipase is but shortly in contact with the ethyl acetate, it is an immobilized formulation that is filtered off at the end of the process.
I would be very thankful for any input ideas/recommendations.
André Delavault
Dear André,
Your EtOAc slowly starts to degrade to EtOH and AcOH due to moisture. If you want to recover and re-use your EtOAc, you could try to store it over activated molecular sieves (4Å) in a tightly sealed flask or round-bottom flask (RBF). Molecular sieves are routinely used in chemistry labs to dry solvents and to keep them dry. If you have access to inert gases (e.g., argon) in your lab, storing the solvent under inert atmosphere would also be beneficial.
The following pre-drying procedure would be even more efficient: dry your used EtOAc over K2CO3, evaporate again, and then store over the aforementioned activated 4Å molecular sieves. Also, in general: before evaporation with the rotavapor, make sure the waste flask (or in your case, where your EtOAc is collected during evaporation) connected to your rotavapor is moisture free (and free from other contaminants, of course!).
Personally, I don't find the following worth the time and effort, but for used EtOAc batches that already contain moisture and the other impurities, the following literature procedure could be useful to remove them: wash with aq. 5 % Na2CO3 , then with a sat. aq. solution of CaCl2 or NaCl and then dry over your MgSO4 or Na2SO4 (or more efficient drying agents, e.g., P2O5 or CaH), distill/evaporate and finally store over 4Å sieves.
See for example: Armarego, W.L.F., "Purification of Laboratory Chemicals", 8th Ed., Elsevier, Oxford (UK), 2017, 154.
Best regards,
J-E Raitanen
It is my experience that many lipases hydrolyze ethyl acetate, especially CAL-B. Can't you use any other non-ester solvent like MIBK or methyl-THF?
Ethyl acetate is degraded into acetic acid and ethanol by hydrolysis with water in acidic and alkaline medium. In water there is slow hydrolysis, so keep it in moisture free atmosphere.
To avoid the hydrolysis of EtOAc by lipase, the immobilized catalyst should be removed by filtration before solvent extraction. Otherwise, you may simply use other solvents for extraction, such as diethyl ether, CH2Cl2, toluene, etc.
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