syn-Propanethial-S-oxide facts for kids

syn-Propanethial S-oxide
IUPAC name	(Z)-propylidene-λ4-sulfanone
Other names	Thiopropanal S-oxide 1-Sulfinylpropane
Identifiers
CAS number	32157-29-2
PubChem	441491
SMILES	O=S=C/CC
InChI InChI=1/C3H6OS/c1-2-3-5-4/h3H,2H2,1H3
Properties
Molecular formula
Molar mass	0 g mol-1
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

syn-Propanethial S-oxide is a special chemical. It is the main reason why your eyes sting and water when you cut onions. This chemical is a type of liquid that easily turns into a gas. When this gas touches your eyes, it makes them tear up.

Why Onions Make You Cry

When you slice an onion, you break open its cells. Inside these cells are different chemicals and special helpers called enzymes.

How the Chemical is Made

When onion cells break, they release enzymes called alliinases. These enzymes start a chain reaction. They break down other chemicals in the onion. This creates something called 1-propenesulfenic acid.

But the story doesn't end there! A second enzyme, called lachrymatory factor synthase (or LFS), quickly changes this acid. It turns it into syn-propanethial S-oxide.

What Happens Next

The syn-propanethial S-oxide quickly turns into a gas. This gas floats up into the air. When it reaches your eyes, it touches the tiny nerves there. These nerves send a signal to your brain. Your brain then tells your tear glands to make tears.

The tears are your body's way of washing away the irritating gas. They help to dilute it and flush it out of your eyes.

Other Plants with Similar Chemicals

Did you know that other plants can also make chemicals that cause tears? For example, a plant called Allium siculum has a similar chemical. It is called syn-butanethial S-oxide. This shows that the Allium family of plants, which includes onions, has some interesting chemical tricks!

See also

In Spanish: Sulfóxido de tiopropanal para niños