Ethanethiol, commonly known as ethyl mercaptan, is an

organosulfur compound Organosulfur chemistry is the study of the properties and synthesis of organosulfur compounds, which are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur der ...

with the formula CH₃CH₂SH. It is a colorless liquid with a distinct odor. Abbreviated EtSH, it consists of an ethyl group (Et), CH₃CH₂, attached to a

thiol In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl grou ...

group, SH. Its structure parallels that of

ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...

, but with

sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...

in place of

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

. 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 (H-bond) is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force. It occurs when a hydrogen (H) atom, Covalent bond, covalently b ...

. 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 chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term ''petroleum'' refers both to naturally occurring un ...

, and may be added to otherwise odorless gaseous products such as

liquefied petroleum gas Liquefied petroleum gas, also referred to as liquid petroleum gas (LPG or LP gas), is a fuel gas which contains a flammable mixture of hydrocarbon gases, specifically propane, Butane, ''n''-butane and isobutane. It can also contain some ...

(LPG) to help warn of gas leaks. At these concentrations, ethanethiol is not harmful.

Preparation

Ethanethiol is prepared by the reaction of

ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon–carbon bond, carbon–carbon doub ...

with

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. Swedish chemist ...

in the presence of various

catalyst Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...

s. It is also prepared commercially by the reaction of

with

gas over an acidic solid catalyst, such as

alumina Aluminium oxide (or aluminium(III) oxide) is a chemical compound of aluminium and oxygen with the chemical formula . It is the most commonly occurring of several aluminium oxides, and specifically identified as aluminium oxide. It is commonly ...

Historic methods

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 barium carbonate and the pigment lithopone, ZnS/BaSO4. ...

saturated with hydrogen sulfide. He is credited with naming the C₂H₅S- group as mercaptum. Ethanethiol can also be prepared by a

halide In chemistry, a halide (rarely halogenide) is a binary chemical compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a fl ...

displacement reaction, where ethyl halide is treated with aqueous sodium bisulfide. This conversion was demonstrated as early as 1840 by

Henri Victor Regnault Henri Victor Regnault (21 July 1810 – 19 January 1878) was a French chemist and physicist best known for his careful measurements of the thermal properties of gases. He was an early thermodynamicist and was mentor to William Thomson in ...

Odor

Ethanethiol has a strongly disagreeable

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

that

humans Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

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 A leek is a vegetable, a cultivar of ''Allium ampeloprasum'', the broadleaf wild leek (synonym (taxonomy), syn. ''Allium porrum''). The edible part of the plant is a bundle of Leaf sheath, leaf sheaths that is sometimes erroneously called a "s ...

onion An onion (''Allium cepa'' , from Latin ), 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 onion which was classifie ...

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

or cooked

cabbage Cabbage, comprising several cultivars of '' Brassica oleracea'', is a leafy green, red (purple), or white (pale green) biennial plant grown as an annual vegetable crop for its dense-leaved heads. It is descended from the wild cabbage ( ''B.& ...

. 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 Butane () is an alkane with the formula C4H10. Butane exists as two isomers, ''n''-butane with connectivity and iso-butane with the formula . Both isomers are highly flammable, colorless, easily liquefied gases that quickly vaporize at ro ...

and

propane Propane () is a three-carbon chain alkane with the molecular formula . It is a gas at standard temperature and pressure, but becomes liquid when compressed for transportation and storage. A by-product of natural gas processing and petroleum ref ...

(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 fuel in the exothermic chemical process of combustion, releasing heat, light, and various reaction Product (chemistry), products. Flames, the most visible portion of the fire, are produced in the combustion re ...

explosion An explosion is a rapid expansion in volume of a given amount of matter associated with an extreme outward release of energy, usually with the generation of high temperatures and release of high-pressure gases. Explosions may also be generated ...

, and

asphyxiation Asphyxia or asphyxiation is a condition of deficient supply of oxygen to the body which arises from abnormal breathing. Asphyxia causes generalized hypoxia, which affects all the tissues and organs, some more rapidly than others. There are ...

. 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 the southernmost Provinces and territories of Canada, province of Canada. Located in Central Canada, Ontario is the Population of Canada by province and territory, country's most populous province. As of the 2021 Canadian census, it ...

, 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 chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...

organic synthesis Organic synthesis is a branch of chemical synthesis concerned with the construction of organic compounds. Organic compounds are molecules consisting of combinations of covalently-linked hydrogen, carbon, oxygen, and nitrogen atoms. Within the gen ...

. In the presence of

sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula . It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly corrosive base (chemistry), ...

, it gives the powerful

nucleophile In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are ...

EtS⁻. The salt sodium ethanethiolate can be generated quantitatively by reaction of ethanethiol with a suspension of sodium hydride in

dimethylformamide Dimethylformamide, DMF is an organic compound with the chemical formula . Its structure is . Commonly abbreviated as DMF (although this initialism is sometimes used for 2,5-dimethylfuran, dimethylfuran, or dimethyl fumarate), this colourless liqui ...

. Ethanethiol can be oxidized to ethyl

sulfonic acid In organic chemistry, sulfonic acid (or sulphonic acid) refers to a member of the class of organosulfur compounds with the general formula , where R is an organic alkyl or aryl group and the group a sulfonyl hydroxide. As a substituent, it is kn ...

, using strong

oxidizing agents An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ''electron donor''). In ot ...

. Weaker oxidants, such as

ferric oxide Iron(III) oxide or ferric oxide is the inorganic compound with the formula . It occurs in nature as the mineral hematite, which serves as the primary source of iron for the steel industry. It is also known as red iron oxide, especially when us ...

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 viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...

give the

disulfide In chemistry, a disulfide (or disulphide in British English) is a compound containing a functional group or the anion. The linkage is also called an SS-bond or sometimes a disulfide bridge and usually derived from two thiol groups. In inorg ...

, 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 In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. The lanthanide and actinid ...

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 convent ...

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

References

External links

NLM Hazardous Substances Databank – Ethyl mercaptan

{{Authority control Flavors Alkanethiols Foul-smelling chemicals