what really happens is that this thiopropenal S-oxide attacks free thiol in one receptor that usually detects spicy smells, much like about any modern tear gas (CN, CS, CR. also allyl isothiocyanate from mustard and many, many, many other alkylating things). there’s no acid involved
Onions spew enzymes and sulfenic acid when their skin is broken. These compounds combine to produce propanethial S-oxide, an irritating gas.
Propanethial S-oxide is a lachrymatory agent, meaning that it generates tears when it touches the eye. Propanethial S-oxide turns into sulfuric acid when it touches the water layer that covers and protects your eyeballs.
this meme is wrong
what really happens is that this thiopropenal S-oxide attacks free thiol in one receptor that usually detects spicy smells, much like about any modern tear gas (CN, CS, CR. also allyl isothiocyanate from mustard and many, many, many other alkylating things). there’s no acid involved
I don’t know whether to believe the meme or the comment on the meme.
Source
I’m not a chemistry guy though.