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ABC of Safety in the Biological Sciences
ETHER PEROXIDES
Diethyl ether, when stored, will produce volatile peroxides which tend to accumulate in the neck of the bottle. An explosion can then occur if the bottle is jarred or when the peroxides are ignited by friction when the bottle is opened.20 An explosion may also occur if ether is distilled while peroxides are present.
To test for ether peroxides:
- Place 10 ml of ferrous thiocyanate in a 300 ml stoppered bottle previously filled with carbon dioxide.
- Completely fill the bottle with the sample of ether.
- Insert the stopper so that no air bubble is enclosed.
- Shake the bottle vigorously and set aside, in the dark, for five minutes.
RESULT: A pink colour in the ether indicates the presence of a peroxide.
TECHNICAL NOTE: Alternatively test strips which detect the presence of peroxides in liquids which produce them are commercially available (for example Perex Test and Merckoquant Peroxide Test).
Peroxides can be removed by treating the solvent with a freshly prepared solution of 25% ferric sulphate. Twenty ml of solution should be used for each litre of hydrocarbon. Aluminium oxide can also be used to remove peroxides from solvents as well as for drying the solvent. 30 gm of aluminium oxide is sufficient to remove the peroxide from 250 ml of diethyl ether. A sodium-lead alloy can also be used but is not recommended as there may be problems with disposing of the lead (which is toxic) after the reaction is complete.
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