organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, ...
, an alkane, or paraffin (a historical
trivial name
In chemistry, a trivial name is a non systematic name for a chemical substance. That is, the name is not recognized according to the rules of any formal system of chemical nomenclature such as IUPAC inorganic or IUPAC organic nomenclature. A ...
saturated
Saturation, saturated, unsaturation or unsaturated may refer to:
Chemistry
* Saturation, a property of organic compounds referring to carbon-carbon bonds
** Saturated and unsaturated compounds
**Degree of unsaturation
** Saturated fat or fatty ac ...
hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
. In other words, an alkane consists of
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
and
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon mak ...
atoms arranged in a
tree
In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...
structure in which all the
carbon–carbon bond
A carbon–carbon bond is a covalent bond between two carbon atoms. The most common form is the single bond: a bond composed of two electrons, one from each of the two atoms. The carbon–carbon single bond is a sigma bond and is formed bet ...
s are
single
Single may refer to:
Arts, entertainment, and media
* Single (music), a song release
Songs
* "Single" (Natasha Bedingfield song), 2004
* "Single" (New Kids on the Block and Ne-Yo song), 2008
* "Single" (William Wei song), 2016
* "Single", by ...
. Alkanes have the general chemical formula . The alkanes range in complexity from the simplest case of
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
(), where ''n'' = 1 (sometimes called the parent molecule), to arbitrarily large and complex molecules, like pentacontane () or 6-ethyl-2-methyl-5-(1-methylethyl) octane, an isomer of
tetradecane
Tetradecane is an alkane hydrocarbon with the chemical formula CH3(CH2)12CH3.
Tetradecane has 1858 structural isomers
In chemistry, a structural isomer (or constitutional isomer in the IUPAC nomenclature) of a compound is another compound w ...
().
The
International Union of Pure and Applied Chemistry
The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
(IUPAC) defines alkanes as "acyclic branched or unbranched hydrocarbons having the general formula , and therefore consisting entirely of hydrogen atoms and saturated carbon atoms". However, some sources use the term to denote ''any'' saturated hydrocarbon, including those that are either monocyclic (i.e. the cycloalkanes) or polycyclic, despite their having a distinct general formula (i.e. cycloalkanes are ).
In an alkane, each carbon atom is sp3-hybridized with 4
sigma bond
In chemistry, sigma bonds (σ bonds) are the strongest type of covalent chemical bond. They are formed by head-on overlapping between atomic orbitals. Sigma bonding is most simply defined for diatomic molecules using the language and tools of s ...
s (either C–C or C–H), and each hydrogen atom is joined to one of the carbon atoms (in a C–H bond). The longest series of linked carbon atoms in a molecule is known as its
carbon skeleton
The skeletal formula, or line-angle formula or shorthand formula, of an organic compound is a type of molecular structural formula that serves as a shorthand representation of a molecule's bonding and some details of its molecular geometry. A ...
or carbon backbone. The number of carbon atoms may be considered as the size of the alkane.
One group of the higher alkanes are
wax
Waxes are a diverse class of organic compounds that are lipophilic, malleable solids near ambient temperatures. They include higher alkanes and lipids, typically with melting points above about 40 °C (104 °F), melting to giv ...
es, solids at standard ambient temperature and pressure (SATP), for which the number of carbon atoms in the carbon backbone is greater than about 17.
With their repeated – units, the alkanes constitute a homologous series of organic compounds in which the members differ in
molecular mass
The molecular mass (''m'') is the mass of a given molecule: it is measured in daltons (Da or u). Different molecules of the same compound may have different molecular masses because they contain different isotopes of an element. The related quanti ...
by multiples of 14.03 u (the total mass of each such methylene-bridge unit, which comprises a single carbon atom of mass 12.01 u and two hydrogen atoms of mass ~1.01 u each).
Methane is produced by methanogenic bacteria and some long-chain alkanes function as pheromones in certain animal species or as protective waxes in plants and fungi. Nevertheless, most alkanes do not have much biological activity. They can be viewed as molecular trees upon which can be hung the more active/reactive
functional group
In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the re ...
s of biological molecules.
The alkanes have two main commercial sources:
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 crud ...
(crude oil) and
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 ...
.
An
alkyl
In organic chemistry, an alkyl group is an alkane missing one hydrogen.
The term ''alkyl'' is intentionally unspecific to include many possible substitutions.
An acyclic alkyl has the general formula of . A cycloalkyl is derived from a cycloa ...
group is an alkane-based molecular fragment that bears one open valence for bonding. They are generally abbreviated with the symbol for any organyl group, R, although Alk is sometimes used to specifically symbolize an alkyl group (as opposed to an alkenyl group or aryl group).
Structure and classification
Ordinarily the C-C single bond distance is .
Saturated hydrocarbons can be linear, branched, or
cyclic
Cycle, cycles, or cyclic may refer to:
Anthropology and social sciences
* Cyclic history, a theory of history
* Cyclical theory, a theory of American political history associated with Arthur Schlesinger, Sr.
* Social cycle, various cycles in s ...
. The third group is sometimes called cycloalkanes. Very complicated structures are possible by combining linear, branch, cyclic alkanes.
Isomerism
Alkanes with more than three
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon mak ...
atoms can be arranged in various ways, forming structural isomers. The simplest isomer of an alkane is the one in which the carbon atoms are arranged in a single chain with no branches. This isomer is sometimes called the ''n''-isomer (''n'' for "normal", although it is not necessarily the most common). However, the chain of carbon atoms may also be branched at one or more points. The number of possible isomers increases rapidly with the number of carbon atoms. For example, for acyclic alkanes:
On-Line Encyclopedia of Integer Sequences
The On-Line Encyclopedia of Integer Sequences (OEIS) is an online database of integer sequences. It was created and maintained by Neil Sloane while researching at AT&T Labs. He transferred the intellectual property and hosting of the OEIS to t ...
* C1:
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
only
* C2:
ethane
Ethane ( , ) is an organic chemical compound with chemical formula . At standard temperature and pressure, ethane is a colorless, odorless gas. Like many hydrocarbons, ethane is isolated on an industrial scale from natural gas and as a petroc ...
isopentane
Isopentane, also called methylbutane or 2-methylbutane, is a branched-chain saturated hydrocarbon (an alkane) with five carbon atoms, with formula or .
Isopentane is an extremely volatile and extremely flammable liquid at room temperature and ...
hexane
Hexane () is an organic compound, a straight-chain alkane with six carbon atoms and has the molecular formula C6H14.
It is a colorless liquid, odorless when pure, and with boiling points approximately . It is widely used as a cheap, relatively ...
2,2-dimethylbutane
2,2-Dimethylbutane, trivially known as neohexane, is an organic compound with formula C6H14 or (H3C-)3-C-CH2-CH3. It is therefore an alkane, indeed the most compact and branched of the hexane isomers — the only one with a quaternary carbon and a ...
, and
2,3-dimethylbutane
2,3-Dimethylbutane is an isomer of hexane. It has the chemical formula
In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, ...
* C7: 9 isomers:
heptane
Heptane or ''n''-heptane is the straight-chain alkane with the chemical formula H3C(CH2)5CH3 or C7H16. When used as a test fuel component in anti-knock test engines, a 100% heptane fuel is the zero point of the octane rating scale (the 100 poin ...
,
methylhexane Methylhexane may refer to either of two chemical compounds:
* 2-Methylhexane
2-Methylhexane ( C7 H16, also known as isoheptane, ethylisobutylmethane) is an isomer of heptane. It is structurally a hexane molecule with a methyl group attached to its ...
(2 isomers),
dimethylpentane Dimethylpentane may refer to:
* 2,2-Dimethylpentane
* 2,3-Dimethylpentane
* 2,4-Dimethylpentane
* 3,3-Dimethylpentane
{{Short pages monitor of the atmospheres of the outer gas planets such as
Jupiter
Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousandth t ...
Uranus
Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus ( Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars), grandfather of Zeus (Jupiter) and father of ...
(1.99% methane, 2.5 ppm ethane) and Neptune (1.5% methane, 1.5 ppm ethane). Titan (1.6% methane), a satellite of Saturn, was examined by the ''Huygens'' probe, which indicated that Titan's atmosphere periodically rains liquid methane onto the moon's surface. Also on Titan, the Cassini mission has imaged seasonal methane/ethane lakes near the polar regions of Titan.
Methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
and
ethane
Ethane ( , ) is an organic chemical compound with chemical formula . At standard temperature and pressure, ethane is a colorless, odorless gas. Like many hydrocarbons, ethane is isolated on an industrial scale from natural gas and as a petroc ...
have also been detected in the tail of the
comet Hyakutake
Comet Hyakutake (, formally designated C/1996 B2) is a comet, discovered on 31 January 1996, that passed very close to Earth in March of that year. It was dubbed the Great Comet of 1996; its passage near the Earth was one of the closest com ...
. Chemical analysis showed that the abundances of ethane and methane were roughly equal, which is thought to imply that its ices formed in interstellar space, away from the Sun, which would have evaporated these volatile molecules. Alkanes have also been detected in meteorites such as carbonaceous chondrites.
Occurrence of alkanes on Earth
Traces of methane gas (about 0.0002% or 1745 ppb) occur in the Earth's atmosphere, produced primarily by methanogenic microorganisms, such as Archaea in the gut of ruminants.
The most important commercial sources for alkanes are natural gas and
oil
An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...
. Natural gas contains primarily methane and ethane, with some propane and butane: oil is a mixture of liquid alkanes and other
hydrocarbons
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or e ...
. These hydrocarbons were formed when marine animals and plants (zooplankton and phytoplankton) died and sank to the bottom of ancient seas and were covered with sediments in an
anoxic
The term anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts:
* Anoxic waters, sea water, fresh water or groundwater that are depleted of diss ...
environment and converted over many millions of years at high temperatures and high pressure to their current form. Natural gas resulted thereby for example from the following reaction:
:C6H12O6 → 3 CH4 + 3 CO2
These hydrocarbon deposits, collected in porous rocks trapped beneath impermeable cap rocks, comprise commercial
oil fields
A petroleum reservoir or oil and gas reservoir is a subsurface accumulation of hydrocarbons contained in porous or fractured rock formations.
Such reservoirs form when kerogen (ancient plant matter) is created in surrounding rock by the presence ...
. They have formed over millions of years and once exhausted cannot be readily replaced. The depletion of these hydrocarbons reserves is the basis for what is known as the
energy crisis
An energy crisis or energy shortage is any significant bottleneck in the supply of energy resources to an economy. In literature, it often refers to one of the energy sources used at a certain time and place, in particular, those that supply n ...
.
Methane is also present in what is called
biogas
Biogas is a mixture of gases, primarily consisting of methane, carbon dioxide and hydrogen sulphide, produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste and food waste. It is a ...
, produced by animals and decaying matter, which is a possible renewable energy source.
Alkanes have a low solubility in water, so the content in the oceans is negligible; however, at high pressures and low temperatures (such as at the bottom of the oceans), methane can co-crystallize with water to form a solid
methane clathrate
Methane clathrate (CH4·5.75H2O) or (8CH4·46H2O), also called methane hydrate, hydromethane, methane ice, fire ice, natural gas hydrate, or gas hydrate, is a solid clathrate compound (more specifically, a clathrate hydrate) in which a large amo ...
(methane hydrate). Although this cannot be commercially exploited at the present time, the amount of combustible energy of the known methane clathrate fields exceeds the energy content of all the natural gas and oil deposits put together. Methane extracted from methane clathrate is, therefore, a candidate for future fuels.
Biological occurrence
Acyclic alkanes occur in nature in various ways.
;Bacteria and archaea
Certain types of bacteria can metabolize alkanes: they prefer even-numbered carbon chains as they are easier to degrade than odd-numbered chains.
On the other hand, certain archaea, the methanogens, produce large quantities of
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
by the metabolism of
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
or other
oxidized
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...
organic compounds. The energy is released by the oxidation of
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
:
:CO2 + 4 H2 → CH4 + 2 H2O
Methanogens are also the producers of
marsh gas
Marsh gas, also known as swamp gas or bog gas, is a mixture primarily of methane and smaller amounts of hydrogen sulfide, carbon dioxide, and trace phosphine that is produced naturally within some geographical marshes, swamps, and bogs.
The surfac ...
cattle
Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus ''Bos''. Adult females are referred to as cows and adult ma ...
and other herbivores, which can release 30 to 50 gallons per day, and of
termite
Termites are small insects that live in colonies and have distinct castes (eusocial) and feed on wood or other dead plant matter. Termites comprise the infraorder Isoptera, or alternatively the epifamily Termitoidae, within the order Blatto ...
s, is also due to methanogens. They also produce this simplest of all alkanes in the intestines of humans. Methanogenic archaea are, hence, at the end of the
carbon cycle
The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. Carbon is the main component of biological compounds as well as a major componen ...
, with carbon being released back into the atmosphere after having been fixed by
photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...
. It is probable that our current deposits of natural gas were formed in a similar way.
;Fungi and plants
Alkanes also play a role, if a minor role, in the biology of the three
eukaryotic
Eukaryotes () are organisms whose Cell (biology), cells have a cell nucleus, nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the ...
groups of organisms:
fungi
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
, plants, and animals. Some specialized yeasts, e.g., ''Candida tropicale'', ''
Pichia
''Pichia'' (''Hansenula'' and ''Hyphopichia'' are obsolete synonyms) is a genus of yeasts in the family Pichiaceae with spherical, elliptical, or oblong acuminate cells. ''Pichia'' is a teleomorph, and forms hat-shaped, hemispherical, or round asc ...
'' sp., ''
Rhodotorula
''Rhodotorula'' is a genus of pigmented yeasts, part of the division Basidiomycota. It is readily identifiable by distinctive orange/red colonies when grown on Sabouraud's dextrose agar (SDA). This distinctive color is the result of pigme ...
'' sp., can use alkanes as a source of carbon or energy. The fungus '' Amorphotheca resinae'' prefers the longer-chain alkanes in aviation fuel, and can cause serious problems for aircraft in tropical regions.
In plants, the solid long-chain alkanes are found in the plant cuticle and
epicuticular wax
Epicuticular wax is a coating of wax covering the outer surface of the plant cuticle in land plants. It may form a whitish film or bloom on leaves, fruits and other plant organs. Chemically, it consists of hydrophobic organic compounds, mainly st ...
of many species, but are only rarely major constituents.EA Baker (1982) Chemistry and morphology of plant epicuticular waxes. pp. 139-165. In "The Plant Cuticle". edited by DF Cutler, KL Alvin and CE Price. Academic Press, London. They protect the plant against water loss, prevent the
leaching
Leaching is the loss or extraction of certain materials from a carrier into a liquid (usually, but not always a solvent). and may refer to:
* Leaching (agriculture), the loss of water-soluble plant nutrients from the soil; or applying a small amou ...
of important minerals by the rain, and protect against bacteria, fungi, and harmful insects. The carbon chains in plant alkanes are usually odd-numbered, between 27 and 33 carbon atoms in length, and are made by the plants by decarboxylation of even-numbered
fatty acid
In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, ...
s. The exact composition of the layer of wax is not only species-dependent but also changes with the season and such environmental factors as lighting conditions, temperature or humidity.
More volatile short-chain alkanes are also produced by and found in plant tissues. The Jeffrey pine is noted for producing exceptionally high levels of ''n''-heptane in its resin, for which reason its distillate was designated as the zero point for one octane rating. Floral scents have also long been known to contain volatile alkane components, and ''n''-nonane is a significant component in the scent of some
rose
A rose is either a woody perennial flowering plant of the genus ''Rosa'' (), in the family Rosaceae (), or the flower it bears. There are over three hundred species and tens of thousands of cultivars. They form a group of plants that can be ...
s. Emission of gaseous and volatile alkanes such as
ethane
Ethane ( , ) is an organic chemical compound with chemical formula . At standard temperature and pressure, ethane is a colorless, odorless gas. Like many hydrocarbons, ethane is isolated on an industrial scale from natural gas and as a petroc ...
hexane
Hexane () is an organic compound, a straight-chain alkane with six carbon atoms and has the molecular formula C6H14.
It is a colorless liquid, odorless when pure, and with boiling points approximately . It is widely used as a cheap, relatively ...
by plants has also been documented at low levels, though they are not generally considered to be a major component of biogenic air pollution.
Edible vegetable oils also typically contain small fractions of biogenic alkanes with a wide spectrum of carbon numbers, mainly 8 to 35, usually peaking in the low to upper 20s, with concentrations up to dozens of milligrams per kilogram (parts per million by weight) and sometimes over a hundred for the total alkane fraction.
;Animals
Alkanes are found in animal products, although they are less important than unsaturated hydrocarbons. One example is the shark liver oil, which is approximately 14%
pristane
Pristane is a natural saturated terpenoid alkane obtained primarily from shark liver oil, from which its name is derived (Latin ''pristis'', "shark"). It is also found in the stomach oil of birds in the order Procellariiformes and in mineral oil ...
(2,6,10,14-tetramethylpentadecane, C19H40). They are important as
pheromone
A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...
s, chemical messenger materials, on which insects depend for communication. In some species, e.g. the support beetle '' Xylotrechus colonus'',
pentacosane
Higher alkanes are alkanes having nine or more carbon atoms. Nonane is the lightest alkane to have a flash point above 25 °C, and is not classified as dangerously flammable.
The term ''higher alkanes'' is sometimes used literally as "alka ...
(C25H52), 3-methylpentaicosane (C26H54) and 9-methylpentaicosane (C26H54) are transferred by body contact. With others like the
tsetse fly
Tsetse ( , or ) (sometimes spelled tzetze; also known as tik-tik flies), are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus ''Glossina'', which are placed in their own family, Glos ...
''Glossina morsitans morsitans'', the pheromone contains the four alkanes 2-methylheptadecane (C18H38), 17,21-dimethylheptatriacontane (C39H80), 15,19-dimethylheptatriacontane (C39H80) and 15,19,23-trimethylheptatriacontane (C40H82), and acts by smell over longer distances. Waggle-dancing
honey bee
A honey bee (also spelled honeybee) is a eusocial flying insect within the genus ''Apis'' of the bee clade, all native to Afro-Eurasia. After bees spread naturally throughout Africa and Eurasia, humans became responsible for the current cosm ...
s produce and release two alkanes, tricosane and pentacosane.
Ecological relations
One example, in which both plant and animal alkanes play a role, is the ecological relationship between the
sand bee
Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of ...
Ophrys sphegodes
''Ophrys sphegodes'', commonly known as the early spider-orchid, is a species of sexually-deceptive orchid native to Europe and the Middle East. It is a very varied species with many subspecies recognised.
Description
Plant height varies with l ...
''); the latter is dependent for
pollination
Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, birds, a ...
on the former. Sand bees use pheromones in order to identify a mate; in the case of ''A. nigroaenea'', the females emit a mixture of
tricosane
Higher alkanes are alkanes having nine or more carbon atoms. Nonane is the lightest alkane to have a flash point above 25 °C, and is not classified as dangerously flammable.
The term ''higher alkanes'' is sometimes used literally as "alka ...
(C23H48),
pentacosane
Higher alkanes are alkanes having nine or more carbon atoms. Nonane is the lightest alkane to have a flash point above 25 °C, and is not classified as dangerously flammable.
The term ''higher alkanes'' is sometimes used literally as "alka ...
(C25H52) and
heptacosane
Higher alkanes are alkanes having nine or more carbon atoms. Nonane is the lightest alkane to have a flash point above 25 °C, and is not classified as dangerously flammable.
The term ''higher alkanes'' is sometimes used literally as "alka ...
(C27H56) in the ratio 3:3:1, and males are attracted by specifically this odor. The orchid takes advantage of this mating arrangement to get the male bee to collect and disseminate its pollen; parts of its flower not only resemble the appearance of sand bees but also produce large quantities of the three alkanes in the same ratio as female sand bees. As a result, numerous males are lured to the blooms and attempt to copulate with their imaginary partner: although this endeavor is not crowned with success for the bee, it allows the orchid to transfer its pollen,
which will be dispersed after the departure of the frustrated male to other blooms.
Production
Petroleum refining
As stated earlier, the most important source of alkanes is natural gas and crude oil. Alkanes are separated in an
oil refinery
An oil refinery or petroleum refinery is an industrial process plant where petroleum (crude oil) is transformed and refined into useful products such as gasoline (petrol), diesel fuel, asphalt base, fuel oils, heating oil, kerosene, lique ...
Fischer–Tropsch process
The Fischer–Tropsch process is a collection of chemical reactions that converts a mixture of carbon monoxide and hydrogen, known as syngas, into liquid hydrocarbons. These reactions occur in the presence of metal catalysts, typically at temperatu ...
is a method to synthesize liquid hydrocarbons, including alkanes, from
carbon monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
and hydrogen. This method is used to produce substitutes for
petroleum distillate
Petrochemicals (sometimes abbreviated as petchems) are the chemical products obtained from petroleum by refining. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable sou ...
s.
Laboratory preparation
There is usually little need for alkanes to be synthesized in the laboratory, since they are usually commercially available. Also, alkanes are generally unreactive chemically or biologically, and do not undergo functional group interconversions cleanly. When alkanes are produced in the laboratory, it is often a side-product of a reaction. For example, the use of ''n''-butyllithium as a strong base gives the conjugate acid ''n''-butane as a side-product:
: C4H9Li + H2O → C4H10 +
LiOH
Lithium hydroxide is an inorganic compound with the formula LiOH. It can exist as anhydrous or hydrated, and both forms are white hygroscopic solids. They are soluble in water and slightly soluble in ethanol. Both are available commercially. While ...
However, at times it may be desirable to make a section of a molecule into an alkane-like functionality (
alkyl
In organic chemistry, an alkyl group is an alkane missing one hydrogen.
The term ''alkyl'' is intentionally unspecific to include many possible substitutions.
An acyclic alkyl has the general formula of . A cycloalkyl is derived from a cycloa ...
group) using the above or similar methods. For example, an ethyl group is an alkyl group; when this is attached to a hydroxy group, it gives
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 ...
, which is not an alkane. To do so, the best-known methods are
hydrogenation
Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organ ...
of
alkene
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
s:
:RCH=CH2 + H2 → RCH2CH3(R =
alkyl
In organic chemistry, an alkyl group is an alkane missing one hydrogen.
The term ''alkyl'' is intentionally unspecific to include many possible substitutions.
An acyclic alkyl has the general formula of . A cycloalkyl is derived from a cycloa ...
)
Alkanes or alkyl groups can also be prepared directly from
alkyl halide
The haloalkanes (also known as halogenoalkanes or alkyl halides) are alkanes containing one or more halogen substituents. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalkanes are widely us ...
Barton–McCombie deoxygenation
The Barton–McCombie deoxygenation is an organic reaction in which a hydroxy functional group in an organic compound is replaced by a hydrogen to give an alkyl group. It is named after British chemists Sir Derek Harold Richard Barton and Stuart ...
removes hydroxyl groups from alcohols e.g.
:
and the
Clemmensen reduction
Clemmensen reduction is a chemical reaction described as a reduction of ketones (or aldehydes) to alkanes using zinc amalgam and concentrated hydrochloric acid. This reaction is named after Erik Christian Clemmensen, a Danish chemist.
The orig ...
removes carbonyl groups from aldehydes and ketones to form alkanes or alkyl-substituted compounds e.g.:
:
Preparation from other organic compounds
Alkanes can be prepared from a variety of organic compounds. These include alkenes, alkynes, haloalkanes, alcohols, aldehydes, ketones and carboxylic acids.
From alkenes and alkynes
Addition of molecular
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
alkene
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
hydrogenation
Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organ ...
reaction is typically performed using a powdered metal
catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
, such as
palladium
Palladium is a chemical element with the symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1803 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas, which was itself na ...
,
platinum
Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver".
Pla ...
, or
nickel
Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow ...
. The reaction is exothermic because the product alkane is more stable. This is an important process in several fields of industrial and research chemistry.
From haloalkanes
Several methods produce alkanes from
haloalkanes
The haloalkanes (also known as halogenoalkanes or alkyl halides) are alkanes containing one or more halogen substituents. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalkanes are widely us ...
.
In the
Wurtz reaction
In organic chemistry, the Wurtz reaction, named after Charles Adolphe Wurtz, is a coupling reaction whereby two alkyl halides are treated with sodium metal to form a higher alkane.
: 2 R−X + 2 Na → R−R + 2 NaX
The reaction is of little ...
, a haloalkane is treated with sodium in dry ether to yield an alkane having double the number of carbon atoms. This reaction proceeds through a free radical intermediate and has the possibility of alkene formation in case of tertiary haloalkanes and vicinal dihalides.
:2 R−X + 2 Na → R−R + 2 Na+X
In
Corey–House synthesis The Corey–House synthesis (also called the Corey–Posner–Whitesides–House reaction and other permutations) is an organic reaction that involves the reaction of a lithium diorganylcuprate (R_CuLi) with an organic pseudohalide (R'-X) to form a ...
, a haloalkane is treated with dialkyl lithium cuprate, a
Gilman reagent
A Gilman reagent is a lithium and copper ( diorganocopper) reagent compound, R2CuLi, where R is an alkyl or aryl. These reagents are useful because, unlike related Grignard reagents and organolithium reagents, they react with organic halides to ...
, to yield a higher alkane:
:Li+ –Cu–R€“ + R'–X → R–R' + R–Cu + Li+X
Haloalkanes can be reduced to alkanes by reaction with
hydride
In chemistry, a hydride is formally the anion of hydrogen( H−). The term is applied loosely. At one extreme, all compounds containing covalently bound H atoms are called hydrides: water (H2O) is a hydride of oxygen, ammonia is a hydride ...
The applications of alkanes depend on the number of carbon atoms. The first four alkanes are used mainly for heating and cooking purposes, and in some countries for electricity generation.
Methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
and
ethane
Ethane ( , ) is an organic chemical compound with chemical formula . At standard temperature and pressure, ethane is a colorless, odorless gas. Like many hydrocarbons, ethane is isolated on an industrial scale from natural gas and as a petroc ...
are the main components of natural gas; they are normally stored as gases under pressure. It is, however, easier to transport them as liquids: This requires both compression and cooling of the gas.
Propane and butane are gases at atmospheric pressure that can be liquefied at fairly low pressures and are commonly known as
liquified petroleum gas
Liquefied petroleum gas (LPG or LP gas) is a fuel gas which contains a flammable mixture of hydrocarbon gases, specifically propane, propylene, butylene, isobutane and n-butane.
LPG is used as a fuel gas in heating appliances, cooking ...
(LPG). Propane is used in propane gas burners and as a fuel for road vehicles, butane in space heaters and disposable cigarette lighters. Both are used as propellants in
aerosol spray
Aerosol spray is a type of dispensing system which creates an aerosol mist of liquid particles. It comprises a can or bottle that contains a payload, and a propellant under pressure. When the container's valve is opened, the payload is forced out ...
s.
From pentane to octane the alkanes are highly volatile liquids. They are used as fuels in
internal combustion engine
An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal c ...
s, as they vaporize easily on entry into the combustion chamber without forming droplets, which would impair the uniformity of the combustion. Branched-chain alkanes are preferred as they are much less prone to premature ignition, which causes Engine knocking, knocking, than their straight-chain homologues. This propensity to premature ignition is measured by the octane rating of the fuel, where 2,2,4-Trimethylpentane, 2,2,4-trimethylpentane (''isooctane'') has an arbitrary value of 100, and
heptane
Heptane or ''n''-heptane is the straight-chain alkane with the chemical formula H3C(CH2)5CH3 or C7H16. When used as a test fuel component in anti-knock test engines, a 100% heptane fuel is the zero point of the octane rating scale (the 100 poin ...
has a value of zero. Apart from their use as fuels, the middle alkanes are also good solvents for nonpolar substances.
Alkanes from
nonane
Nonane is a linear alkane hydrocarbon with the chemical formula C9H20. It is a colorless, flammable liquid, occurring primarily in the component of the petroleum distillate fraction commonly called kerosene, which is used as a heating, tractor, ...
to, for instance,
hexadecane
Hexadecane (also called cetane) is an alkane hydrocarbon with the chemical formula C16H34. Hexadecane consists of a chain of 16 carbon atoms, with three hydrogen atoms bonded to the two end carbon atoms, and two hydrogens bonded to each of the ...
(an alkane with sixteen carbon atoms) are liquids of higher viscosity, less and less suitable for use in gasoline. They form instead the major part of Diesel fuel, diesel and aviation fuel. Diesel fuels are characterized by their cetane number, cetane being an old name for hexadecane. However, the higher melting points of these alkanes can cause problems at low temperatures and in polar regions, where the fuel becomes too thick to flow correctly.
Alkanes from hexadecane upwards form the most important components of fuel oil and lubricating oil. In the latter function, they work at the same time as anti-corrosive agents, as their hydrophobic nature means that water cannot reach the metal surface. Many solid alkanes find use as paraffin wax, for example, in candles. This should not be confused however with true
wax
Waxes are a diverse class of organic compounds that are lipophilic, malleable solids near ambient temperatures. They include higher alkanes and lipids, typically with melting points above about 40 °C (104 °F), melting to giv ...
, which consists primarily of esters.
Alkanes with a chain length of approximately 35 or more carbon atoms are found in bitumen, used, for example, in road surfacing. However, the higher alkanes have little value and are usually split into lower alkanes by Cracking (chemistry), cracking.
Some synthetic polymers such as polyethylene and polypropylene are alkanes with chains containing hundreds or thousands of carbon atoms. These materials are used in innumerable applications, and billions of kilograms of these materials are made and used each year.
Environmental transformations
Alkanes are chemically very inert apolar molecules which are not very reactive as organic compounds. This inertness yields serious ecological issues if they are released into the environment. Due to their lack of functional groups and low water solubility, alkanes show poor bioavailability for microorganisms.
There are, however, some microorganisms possessing the metabolic capacity to utilize ''n''-alkanes as both carbon and energy sources. Some bacterial species are highly specialised in degrading alkanes; these are referred to as hydrocarbonoclastic bacteria.
Hazards
Methane is flammable, explosive and dangerous to inhale; because it is a colorless, odorless gas, special caution must be taken around methane. Ethane is also extremely flammable, explosive, and dangerous to inhale. Both of them may cause suffocation. Propane, too, is flammable and explosive, and may cause drowsiness or unconsciousness if inhaled. Butane presents the same hazards as propane.
Alkanes also pose a threat to the environment. Branched alkanes have a lower biodegradability than unbranched alkanes. Methane is considered to be the greenhouse gas that is most dangerous to the environment, although the amount of methane in the atmosphere is relatively low.