Syn-Propanethial-S-oxide
syn-Propanethial S-oxide, a member of a class of organosulfur compounds known as thiocarbonyl S-oxides, is a volatile liquid that acts as a lachrymatory agent.
Onion release
The chemical is released from onions, Allium cepa, as they are sliced. The release is due to the breaking open of the onion cells, which releases enzymes called alliinases. Alliinases then break down amino acid sulfoxides, generating sulfenic acids. A specific sulfenic acid, allicin or 1-propenesulfenic acid, is rapidly rearranged by another enzyme, the lachrymatory factor synthase, to give syn-propanethial S-oxide. Vapors from this volatile liquid induce tearing.Related compounds
A structurally related lachrymatory compound, syn-butanethial S-oxide, C4H8OS, has been found in another onion relative plant, Allium siculum.Propanethial S-oxide forms a stable dimer, trans-3,4-diethyl-1,2-dithietane 1,1-dioxide.