Ethanethiol is the organic compound with the formula CH3CH2SH. It consists of an ethyl group, CH3CH2, attached to a thiol group, SH. The compound is structurally similar to ethanol by replacement of O by S. This change leads to many different properties, the most infamous of which is the strong odour of EtSH. Ethanethiol is also more volatile than ethanol due to its diminished ability to engage in hydrogen bonding. Ethanethiol is toxic. It occurs naturally as a minor component of petroleum, and may be added to liquefied petroleum gas (LPG) to warn of a gas leak. At these concentrations, ethanethiol is not harmful.


Ethanethiol has a strongly disagreeable odour that humans can detect in minute concentrations. The threshold for human detection is as low as one part in 2.8 billion parts of air. Its odour resembles that of leeks or onions. Ethanethiol is intentionally added to butane and propane (see: LPG) to impart an easily noticed smell to these odourless fuels, that otherwise pose the threat of fire and explosion.

According to the 2000 edition of the Guinness Book Of World Records, ethanethiol is the "smelliest substance" in existence. Other more specialized chemicals were probably not examined, however. Most volatile thiols are comparably offensive. Thiols can be oxidized to sulfoxides, which have only a faint smell, using bleach or related oxidants.


Ethanethiol is a valued reagent in organic synthesis. In the presence of sodium hydroxide, it forms the powerful nucleophile NaSEt. The salt can also be generated quantitatively by reaction with sodium hydride.

Mild oxidation of EtSH gives the disulfide, diethyl disulfide:

2 EtSH + H2O2 → EtS-SEt + 2 H2O
Like other thiols, it behaves comparably to hydrogen sulfide. For example, it binds, concomitant with deprotonation to "soft" transition metal cations, such as Hg2+, Cu+, and Ni2+ to give polymeric thiolato complexes, Hg(SEt)2, CuSEt, and Ni(SEt)2, respectively.


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