A strained three-atom ring sterilises syringes and underpins detergents
Ethylene oxide is just two carbons and an oxygen bent into a tight triangle. That strain makes it eager to snap open and react, which is why it can kill microbes on plastic syringes that steam would melt, and why industry turns it into antifreeze, detergents and PEG. The same eagerness makes it carcinogenic and explosive.
Chemically it is the simplest epoxide, formula C2H4O: a colourless, flammable gas with a faint sweet smell, which people can detect once it tops about 500 parts per million in air. Its ring angles sit near 60 degrees, far tighter than the roughly 110 to 120 degrees oxygen prefers in alcohols and ethers, storing strain energy of about 105 kJ/mol. Relieving that strain drives almost everything it does. Add a trace of dilute acid to its water solution and ethylene glycol forms even at room temperature; with ammonia it gives ethanolamines, with fatty alcohols it builds surfactants, and with trimethylamine and water it yields choline.
The French chemist Charles-Adolphe Wurtz first made it in 1859, from 2-chloroethanol and potassium hydroxide. He wrongly believed it behaved like an organic base, an error that lasted until Georg Bredig showed in 1896 that it was not an electrolyte. For decades Wurtz's route was the only one; direct oxidation of ethylene over a silver catalyst, found by Theodore Lefort in 1931, has carried almost all industrial output since 1940. The First World War first made it important, as the precursor to both the coolant ethylene glycol and mustard gas, and in 1938 Lloyd Hall patented its use to sterilise spices.
Its dangers are serious. At room temperature it is flammable, carcinogenic, mutagenic, irritating and anaesthetic, and it is explosive enough to serve as the main ingredient of thermobaric weapons, so it usually travels as a refrigerated liquid. Hospitals still depend on it for heat-sensitive equipment, but its cancer risk keeps that use controversial.
Food is where regulation splits. Some countries fumigate food with it to kill pathogens; others ban the practice. Exporters stress trade and preventing foodborne illness, importers stress domestic safety, and the resulting patchwork of residue limits for the gas and its by-product 2-chloroethanol has led to treated shipments being turned away. Its polymer cousin, poly(ethylene oxide), is meanwhile being tested in separators for lithium-sulfur batteries.
Source: Ethylene oxide
