Question

Question. (A true story.) An inexperienced graduate student moved into a laboratory and began work. He needed some diethyl ether for a reaction, so he opened an old, rusty 1-gallon can marked “ethyl ether” and found there was half a gallon left. To purify the ether, the student set up a distillation apparatus, started a careful distillation, and went to the stockroom for the other reagents he needed. While he was at the stockroom, the student heard a muffled “boom”. He quickly returned to his lab to find a worker from another laboratory putting out a fire. Most of the distillation apparatus was embedded in the ceiling.

(a) Explain what probably happened.

(b) Explain how this near disaster might have been prevented.

Short answer

Answer

(a) Ethers form peroxides on long-term exposure to air, and peroxides are explosive when heated.

(b) Peroxide formation can be prevented by excluding oxygen. Peroxides can also be destroyed by treatment with reducing agents.

Step-by-step solution

Distillation

Distillation is the kind of process in which a liquid is converted into vapors, and these vapors are again condensed to form a liquid.This process starts by heating of liquid to its boiling point.

Cause of explosion

(a) Ethers tend to form peroxides on long-term exposure to air which are unstable species due to very reactive O-O bond present in them. When this bond breaks, peroxides decompose into reactive oxygen species, free radicals, and are highly reactive. Peroxides are explosive when concentrated or heated, and for this reason, ethers should never be distilled to dryness.

Prevention of explosion

(b) Peroxide formation can be prevented by excluding oxygen. Peroxides can be easily destroyed in a safe manner by treating them with reducing agents such as ferrous sulphate or sodium metabisulphite. Also, potassium iodide can also be added in ethers to remove peroxides.