''tert''-Butylthiol, also known as 2-methylpropane-2-thiol, 2-methyl-2-propanethiol, ''tert''-butyl mercaptan (TBM), and ''t''-BuSH, is an organosulfur compound with the formula (CH
3)
3CSH. This
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 gro ...
is used as an
odorant
An aroma compound, also known as an odorant, aroma, fragrance or flavoring, is a chemical compound that has a smell or odor. For an individual chemical or class of chemical compounds to impart a smell or fragrance, it must be sufficiently vol ...
for
natural gas
Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
, which is otherwise odorless. It may also have been used as a flavoring agent.
Preparation
At least one publication has listed ''tert''-butylthiol as a very minor component of cooked potatoes, but because the ''tert''-butyl moiety is very rare in natural products, other sources doubt the existence of natural sources of the compound. It was first prepared in 1890 by Leonard Dobbin by the reaction of zinc sulfide and ''t''-butyl chloride.
The compound was later prepared in 1932 by the reaction of the
Grignard reagent
A Grignard reagent or Grignard compound is a chemical compound with the general formula , where X is a halogen and R is an organic group, normally an alkyl or aryl. Two typical examples are methylmagnesium chloride and phenylmagnesium bromide ...
, ''t''-BuMgCl, with sulfur to give the corresponding thiolate, followed by
hydrolysis
Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...
. This preparation is shown below:
:''t''-BuMgCl + S → ''t''-BuSMgCl
:''t''-BuSMgCl + H
2O → ''t''-BuSH + Mg(OH)Cl
It is currently prepared industrially by the reaction of
isobutylene
Isobutylene (or 2-methylpropene) is a hydrocarbon with the chemical formula . It is a four-carbon branched alkene (olefin), one of the four isomers of butylene. It is a colorless flammable gas, and is of considerable industrial value.
Productio ...
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 unde ...
over a clay (silica alumina) catalyst.
Reactions
''tert''-Butylthiol can react with metal
alkoxide
In chemistry, an alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They are written as , where R is the organic substituent. Alkoxides are strong bases and, whe ...
s and
acyl chloride
In organic chemistry, an acyl chloride (or acid chloride) is an organic compound with the functional group . Their formula is usually written , where R is a side chain. They are reactive derivatives of carboxylic acids (). A specific example o ...
s to form thiol esters, as shown in the equation:
:
![Thallium(I) 2-methylpropane-2-thiolate synthesis](https://upload.wikimedia.org/wikipedia/commons/2/20/Thallium%28I%29_2-methylpropane-2-thiolate_synthesis.svg)
:
![Thallium(I) 2-methylpropane-2-thiolate reaction](https://upload.wikimedia.org/wikipedia/commons/9/9e/Thallium%28I%29_2-methylpropane-2-thiolate_reaction.svg)
In the reaction above, thallium(I) ethoxide converts to thallium(I) ''t''-butylthiolate. In the presence of
diethyl ether
Diethyl ether, or simply ether, is an organic compound in the ether class with the formula , sometimes abbreviated as (see Pseudoelement symbols). It is a colourless, highly volatile, sweet-smelling ("ethereal odour"), extremely flammable liq ...
,
thallium
Thallium is a chemical element with the Symbol (chemistry), symbol Tl and atomic number 81. It is a gray post-transition metal that is not found free in nature. When isolated, thallium resembles tin, but discolors when exposed to air. Chemists W ...
(I) ''t''-butylthiolate reacts with
acyl chloride
In organic chemistry, an acyl chloride (or acid chloride) is an organic compound with the functional group . Their formula is usually written , where R is a side chain. They are reactive derivatives of carboxylic acids (). A specific example o ...
s to give the corresponding tert-butyl thioesters.
Like other thioesters, it reverts to tert-butylthiol by hydrolysis.
Lithium 2-methylpropane-2-thiolate can be prepared by treatment of ''tert''-butylthiol with
lithium hydride
Lithium hydride is an inorganic compound with the formula Li H. This alkali metal hydride is a colorless solid, although commercial samples are grey. Characteristic of a salt-like (ionic) hydride, it has a high melting point, and it is not solub ...
in an aprotic solvent such as
hexamethylphosphoramide
Hexamethylphosphoramide, often abbreviated HMPA, is a phosphoramide (an amide of phosphoric acid) with the formula This colorless liquid is a useful reagent in organic synthesis.
Structure and reactivity
HMPA is the oxide of the highly basic t ...
(HMPA). The resulting thiolate salt is a useful
demethylating reagent. For example, treatment with
7-methylguanosine gives
guanosine
Guanosine (symbol G or Guo) is a purine nucleoside comprising guanine attached to a ribose (ribofuranose) ring via a β-N9-glycosidic bond. Guanosine can be phosphorylated to become guanosine monophosphate (GMP), cyclic guanosine monophosphate (c ...
. Other ''N''-methylated nucleosides in tRNA are not
demethylated Demethylation is the chemical process resulting in the removal of a methyl group (CH3) from a molecule. A common way of demethylation is the replacement of a methyl group by a hydrogen atom, resulting in a net loss of one carbon and two hydrogen ato ...
by this reagent.
:
Metal complexes
The anion derived from ''tert''-butylthiol forms complexes with various metals. One example is tetrakis(''tert''-butylthiolato)molybdenum(IV), Mo(''t''-BuS)
4. This complex was prepared by treating MoCl
4 with ''t''-BuSLi:
:MoCl
4 + 4 ''t''-BuSLi → Mo(''t''-BuS)
4 + 4 LiCl
Mo(''t''-BuS)
4 is a dark red
diamagnetic
Diamagnetic materials are repelled by a magnetic field; an applied magnetic field creates an induced magnetic field in them in the opposite direction, causing a repulsive force. In contrast, paramagnetic and ferromagnetic materials are attracted ...
complex that is sensitive to air and moisture. The
molybdenum
Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lea ...
center has a distorted tetrahedral coordination to four sulfur atoms, with overall ''D''
2 symmetry.
:
Safety
Even in well ventilated areas, extreme caution must be made when handling ''tert''-butylthiol as it is a highly odorous chemical with an odor threshold of <0.33 ppb. Extreme caution is not due to toxicity, but due to the significant odor and the concern this odor could cause to individuals that might be exposed. The
PEL for thiols of most types is 500 ppb, primarily due to reaction of nausea at levels of 2–3 ppm.
Commercial use
''tert''-Butylthiol is the main ingredient in many gas odorant blends. It is always utilized as a blend of other compounds, typically
dimethyl sulfide,
methyl ethyl sulfide
In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in man ...
,
tetrahydrothiophene
Tetrahydrothiophene is an organosulfur compound with the formula (CH2)4S. The molecule consists of a five-membered saturated ring with four methylene groups and a sulfur atom. It is the saturated analog of thiophene. It is a volatile, colorles ...
or other mercaptans such as
isopropyl mercaptan
In organic chemistry, propyl is a three-carbon alkyl substituent with chemical formula for the linear form. This substituent form is obtained by removing one hydrogen atom attached to the terminal carbon of propane. A propyl substituent is often ...
,
''sec''-butyl mercaptan and/or
''n''-butyl mercaptan, due to its rather high melting point of . These blends are used only with natural gas and not propane, as the boiling points of these blends and propane are quite different. Because propane is delivered as a liquid and vaporizes to gas when it is delivered to the appliance, the vapor liquid equilibrium would substantially reduce the amount of odorant blend in the vapor.
''tert''-Butylthiol has been listed on the
European Food Safety Authority
The European Food Safety Authority (EFSA) is the agency of the European Union (EU) that provides independent scientific advice and communicates on existing and emerging risks associated with the food chain. EFSA was established in February 2002, ...
(FL-no: 12.174) as a flavor additive. There is no indication of what flavor(s) it may have been used in. It has been removed from this list.
See also
*
Butanethiol
1-Butanethiol, also known as butyl mercaptan, is a volatile, clear to yellowish liquid with a fetid (extremely foul-smelling) odor, commonly described as " skunk" odor. In fact, 1-butanethiol is structurally similar to several major constituents ...
(butyl mercaptan)
*
Ethanethiol
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 s ...
(ethyl mercaptan)
References
{{DEFAULTSORT:Butylthiol, tert-
Alkanethiols
Tert-butyl compounds
Foul-smelling chemicals