Peroxides and Ethers

The following is from CRC Handbook of Laboratory Safety, 5th Edition.  Furr, A. Keith.

Ethers

Ethers represent a class of materials which can become more dangerous with prolonged storage because they tend to form explosive peroxides with age.  Exposure to light and air enhance the formation of the peroxides.  A partially empty container increases the amount of air available, and hence the rate at which peroxides will form in the container.  It is preferable, therefore, to use small containers which can be completely emptied, rather than take the amounts needed for immediate use from a large container over a period of time, unless the rate of use is sufficiently high so that peroxides will have a minimal time in which to form. 

Ethyl ether, isopropyl ether, tetrahydrofuran, and many other ethers tend to absorb and react with oxygen from the air to form unstable peroxides which may detonate with extreme violence when they become concentrated by evaporation or distillation, when combined with other compounds that give a detonatable mixture, or when disturbed by unusual heat, shock, or friction.  Peroxides formed in compounds by autoxidation have caused many laboratory accidents, including unexpected explosions of the residue of solvents after distillation, and have caused a number of hazardous disposal operations.  Some of the incidents of discovery and disposal of peroxides in ethers have been reported in the literature, some in personal communications, and some in the newspapers.  An “empty” 250-cc bottle which had held ethyl ether exploded (without injury) when the ground glass stopper was replaced.  Another explosion cost a graduate student the total sight of one eye and most of the sight of the other, and a third explosion killed a research chemist when he attempted to unscrew the cap from an old bottle of isopropyl ether.  

Formation of Peroxides

Peroxides may form in freshly distilled and undistilled and unstablized ethers within less than 2 weeks, and it has been reported that peroxide formation began in tetrahydrofuran after 3 days and in ethyl ether after 8 days.  Exposure to air, as in open and partially emptied containers, accelerates the formation of peroxides in ethers, and while the effect of exposure to light does not seem to be fully understood, it is generally recommended that ethers which will form peroxides should be stored in full, air-tight, amber glass bottles, preferable in the dark.

Although ethyl ether is frequently stored under refrigeration, there is no evidence that refrigerated storage will prevent formation of peroxides, and leaks can result in explosive mixtures in refrigerators since the flash point of ethyl ether is -45 ° C (-49 ° F). 

Isopropyl ether seems unusually susceptible to peroxide and there are reports that a half-filled 500-ml bottle of isopropyl ether peroxidized despite being kept over a wad of iron wool.  Although it may be possible to stabilize isopropyl ether in other ways, the absence of a stabilizer may not always be obvious from the appearance of a sample, so that even opening a container of isopropyl of uncertain vintage to test for peroxides can be hazardous.  C.R. Noller in Chemistry of Organic Compounds, W.B. Saunders, Philadelphia, 1951, comments that “neither hydrogen peroxide, hydroperoxide nor the hydroxyalkyl peroxide are as violently explosive as the peroxidic residues from oxidized ether.”

There are methods of detecting, estimating and removing peroxides, however the safest method is to call UAF Hazardous Materials, 474-5617 to perform the appropriate action.

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