Syn-propanethial-S-oxide

Syn-propanethial-S-oxide is a volatile gas that triggers the tears when an onion is cut. As onions are sliced, cells are broken, allowing enzymes called alliinases to break down amino acid sulfoxides and generate sulfenic acids . Sulfenic acids are unstable and spontaneously rearrange into syn-propanethial-S-oxide. The gas dissipates through the air and eventually reaches the eye, where it reacts with the water to form a dilute solution of sulfuric acid.^{[citation needed]} This acid irritates the nerve endings in the eye, making them sting. Tear glands produce tears to dilute and flush out the irritant.^[1]

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Properties

Syn-propanethial-S-oxide has a chemical formula of C₃H₆OS. It is a slightly flammable gas and can be controlled by burning a candle near a person cutting onions.^{[citation needed]} Leeks do not contain as much of the chemical as onions.^{[citation needed]}

See also

• Allicin

References

1. ^ Scott, Thomas. What is the chemical process that causes my eyes to tear when I peel an onion?. Ask the Experts: Chemistry. Scientific American. Retrieved on 2007-04-28.