Ethanethiol, commonly known as ethyl mercaptan, is an organosulfur compound with the formula CH₃CH₂SH. is a colorless liquid with a distinct odor. Abbreviated EtSH, it consists of an ethyl group (Et), CH₃CH₂, attached to a thiol group, SH. Its structure parallels that of

ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a h ...

, but with

sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...

in place of

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as we ...

. The odor of EtSH is infamous. Ethanethiol is more volatile than ethanol due to a diminished ability to engage in

hydrogen bonding In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing ...

. Ethanethiol is toxic in high concentrations. It occurs naturally as a minor component of

petroleum Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crude ...

, and may be added to otherwise odorless gaseous products such as liquefied petroleum gas (LPG) to help warn of gas leaks. At these concentrations, ethanethiol is not harmful.

Preparation

Ethanethiol is prepared by the reaction of ethene with

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The und ...

over a catalyst. The various producers utilize different catalysts in this process. It has also been prepared commercially by the reaction of

with

gas over an acidic solid catalyst, such as alumina. Ethanethiol was originally reported by Zeise in 1834. Zeise treated calcium ethyl sulfate with a suspension of

barium sulfide Barium sulfide is the inorganic compound with the formula Ba S. BaS is the barium compound produced on the largest scale. It is an important precursor to other barium compounds including BaCO3 and the pigment lithopone, ZnS/BaSO4. Like other ...

saturated with hydrogen sulfide. He is credited with naming the C₂H₅S- group as mercaptum. Ethanethiol can also be prepared by a halide displacement reaction, where ethyl halide is treated with aqueous

sodium bisulfide Sodium hydrosulfide is the chemical compound with the formula NaHS. This compound is the product of the half-neutralization of hydrogen sulfide () with sodium hydroxide (NaOH). NaSH and sodium sulfide are used industrially, often for similar purp ...

. This conversion was demonstrated as early as 1840 by Henri Victor Regnault.

Odor

Ethanethiol has a strongly disagreeable

odor An odor (American English) or odour (Commonwealth English; see spelling differences) is caused by one or more volatilized chemical compounds that are generally found in low concentrations that humans and animals can perceive via their sense ...

that

humans Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...

can detect in minute concentrations. The threshold for human detection is as low as one part in 2.8 billion parts of air (0.36 parts per billion). Its odor resembles that of

leek The leek is a vegetable, a cultivar of '' Allium ampeloprasum'', the broadleaf wild leek (syn. ''Allium porrum''). The edible part of the plant is a bundle of leaf sheaths that is sometimes erroneously called a stem or stalk. The genus ''All ...

onion An onion (''Allium cepa'' L., from Latin ''cepa'' meaning "onion"), also known as the bulb onion or common onion, is a vegetable that is the most widely cultivated species of the genus ''Allium''. The shallot is a botanical variety of the oni ...

durian The durian (, ) is the edible fruit of several tree species belonging to the genus ''Durio''. There are 30 recognised ''Durio'' species, at least nine of which produce edible fruit. '' Durio zibethinus'', native to Borneo and Sumatra, is the o ...

or cooked cabbage, but is quite distinct. Employees of the Union Oil Company of California reported first in 1938 that turkey vultures would gather at the site of any gas leak. After finding that this was caused by traces of ethanethiol in the gas it was decided to boost the amount of ethanethiol in the gas, to make detection of leaks easier.

Uses

Ethanethiol is intentionally added to butane and

propane Propane () is a three-carbon alkane with the molecular formula . It is a gas at standard temperature and pressure, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as ...

(see: LPG) to impart an easily noticed smell to these normally odorless fuels that pose the threat of

fire Fire is the rapid oxidation of a material (the fuel) in the exothermic chemical process of combustion, releasing heat, light, and various reaction Product (chemistry), products. At a certain point in the combustion reaction, called the ignition ...

, explosion, and asphyxiation. In the underground mining industry, ethanethiol or ethyl mercaptan is referred to as "stench gas". The gas is released into mine ventilation systems during an emergency to alert mine workers. In

Ontario Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central C ...

, mining legislation dictates that "The alarm system in an underground mine shall, consist of the introduction into all workplaces of sufficient quantities of ethyl mercaptan gas or similar gas to be readily detectable by all workers".

Reactions

Ethanethiol is a reagent in

organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...

. In the presence of sodium hydroxide, it gives the powerful nucleophile EtS⁻. The salt can be generated quantitatively by reaction with sodium hydride. Ethanethiol can be oxidized to ethyl sulfonic acid, using strong oxidizing agents. Weaker oxidants, such as ferric oxide or

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3% ...

give 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

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

s, such as Hg²⁺, Cu⁺, and Ni²⁺ to give polymeric thiolato complexes, Hg(SEt)₂, CuSEt, and Ni(SEt)₂, respectively.

References

External links