Peroxides in ethyl acetate

Lindsay A. Hobson
University of Texas, Austin

Chemical & Engineering News (18 Dec 2000) Vol. 78, No. 51, pp. 2.

During the past several months, we have observed that certain reactions that normally worked well in our laboratory would occasionally give different results. Eventually, through considerable chemical detective work, we were able to locate the culprit: peroxides in various batches of ACS-grade ethyl acetate. For example, oxidation of a sulfide to a sulfoxide using m- chloroperoxybenzoic acid in dichloromethane would work very well, but when the crude product was chromatographed over silica gel eluting with ethyl acetate that contained peroxides, large amounts of the corresponding sulfone formed. We have also observed amines being oxidized to N-oxides, and Baeyer-Villiger-like oxidations. Therefore, it seems most likely that the peroxide impurity is peracetic acid formed by autooxidation of ethanol (from hydrolysis) to acetaldehyde and then to peracetic acid (Fieser, L. F., et al. "Fiesers' Reagents for Organic Synthesis." Vol. 1, New York: John Wiley & Sons, 1967, 787).

Testing batches of ACS-grade ethyl acetate revealed that some (not all) contained peracetic acid as judged from a peroxide test kit (Quantofix peroxide 25). The levels were approximately 0.5 mg per L.

Apparently, the suppliers are aware of this problem, but since ACS does not require specification of peroxide levels in ethyl acetate, the suppliers have not informed researchers. This is not a trivial problem. Apart from the examples referred to above, the unknown presence of peroxides can be extremely hazardous.

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