Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon.[1]: 620 Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic; their odor is usually faint, and may be similar to that of gasoline or lighter fluid. They occur in a diverse range of molecular structures and phases: they can be gases (such as methane and propane), liquids (such as hexane and benzene), low melting solids (such as paraffin wax and naphthalene) or polymers (such as polyethylene and polystyrene).
In the
Types
As defined by the International Union of Pure and Applied Chemistry's nomenclature of organic chemistry, hydrocarbons are classified as follows:
- 3-methylhexane and its higher homologues, branched hydrocarbons can be chiral.[1]: 627 Chiral saturated hydrocarbons constitute the side chains of biomolecules such as chlorophyll and tocopherol.[2]
- Unsaturated hydrocarbons, which have one or more double or triple bonds between carbon atoms. Those with one or more double bonds are called alkenes. Those with one double bond have the formula CnH2n (assuming non-cyclic structures).[1]: 628 Those containing triple bonds are called alkyne. Those with one triple bond have the formula CnH2n−2.[1]: 631
- aromatic ring. 10% of total nonmethane organic carbon emission are aromatic hydrocarbons from the exhaust of gasoline-powered vehicles.[3]
The term 'aliphatic' refers to non-aromatic hydrocarbons. Saturated aliphatic hydrocarbons are sometimes referred to as 'paraffins'. Aliphatic hydrocarbons containing a double bond between carbon atoms are sometimes referred to as 'olefins'.
Number of carbon atoms |
Alkane (single bond) | Alkene (double bond) | Alkyne (triple bond) | Cycloalkane | Alkadiene
|
---|---|---|---|---|---|
1 | Methane | — | — | — | — |
2 | Ethane | Ethene (ethylene) |
Ethyne (acetylene) | — | — |
3 | Propane | Propene (propylene) |
Propyne (methylacetylene) |
Cyclopropane | Propadiene (allene) |
4 | Butane | Butene (butylene) | Butyne | Cyclobutane | Butadiene
|
5 | Pentane | Pentene | Pentyne | Cyclopentane | Pentadiene (piperylene) |
6 | Hexane | Hexene | Hexyne | Cyclohexane | Hexadiene
|
7 | Heptane | Heptene | Heptyne | Cycloheptane | Heptadiene |
8 | Octane | Octene | Octyne | Cyclooctane | Octadiene
|
9 | Nonane | Nonene | Nonyne | Cyclononane | Nonadiene |
10 | Decane | Decene | Decyne | Cyclodecane | Decadiene |
11 | Undecane | Undecene | Undecyne | Cycloundecane | Undecadiene |
12 | Dodecane | Dodecene |
Dodecyne | Cyclododecane | Dodecadiene |
Usage
The predominant use of hydrocarbons is as a combustible
Some large-scale non-fuel applications of hydrocarbons begin with ethane and propane, which are obtained from petroleum and natural gas. These two gases are converted either to syngas or to ethylene and propylene respectively. Global consumption of benzene in 2021 is estimated at more than 58 million metric tons, which will increase to 60 million tons in 2022.[4]
Hydrocarbons are also prevalent in nature. Some eusocial arthropods, such as the Brazilian stingless bee,
There is also potential to harvest hydrocarbons from plants like
Reactions
The noteworthy feature of saturated hydrocarbons is their inertness. Unsaturated hydrocarbons (alkanes, alkenes and aromatic compounds) react more readily, by means of substitution, addition, polymerization. At higher temperatures they undergo dehydrogenation, oxidation and combustion.
Substitution
Of the classes of hydrocarbons, aromatic compounds uniquely (or nearly so) undergo substitution reactions. The chemical process practiced on the largest scale is the reaction of benzene and
- C6H6 + C2H4 → C6H5CH2CH3
The resulting ethylbenzene is dehydrogenated to styrene and then polymerized to manufacture polystyrene, a common thermoplastic material.
Free-radical substitution
Substitution reactions occur also in saturated hydrocarbons (all single carbon–carbon bonds). Such reactions require highly reactive reagents, such as
- CH4 + Cl2 → CH3Cl + HCl
- CH3Cl + Cl2 → CH2Cl2 + HCl
all the way to CCl4 (carbon tetrachloride)
- C2H6 + Cl2 → C2H5Cl + HCl
- C2H4Cl2 + Cl2 → C2H3Cl3 + HCl
all the way to C2Cl6 (hexachloroethane)
Addition
Addition reactions apply to alkenes and alkynes. In this reaction a variety of reagents add "across" the pi-bond(s). Chlorine, hydrogen chloride, water, and hydrogen are illustrative reagents.
Addition polymerization
Hydrogenation
Metathesis
Some hydrocarbons undergo metathesis, in which substituents attached by C–C bonds are exchanged between molecules. For a single C–C bond it is alkane metathesis, for a double C–C bond it is alkene metathesis (olefin metathesis), and for a triple C–C bond it is alkyne metathesis.
High-temperature reactions
Cracking
Dehydrogenation
Pyrolysis
Combustion
Combustion of hydrocarbons is currently the main source of the world's energy for
Common properties of hydrocarbons are the facts that they produce steam, carbon dioxide and heat during combustion and that oxygen is required for combustion to take place. The simplest hydrocarbon, methane, burns as follows:
In inadequate supply of air, carbon black and water vapour are formed:
And finally, for any
Partial oxidation characterizes the reactions of alkenes and oxygen. This process is the basis of rancidification and paint drying.
Benzene burns with sooty flame when heated in air:
Origin
The vast majority of hydrocarbons found on
A seemingly limitless variety of compounds comprise petroleum, hence the necessity of refineries. These hydrocarbons consist of saturated hydrocarbons, aromatic hydrocarbons, or combinations of the two. Missing in petroleum are alkenes and alkynes. Their production requires refineries. Petroleum-derived hydrocarbons are mainly consumed for fuel, but they are also the source of virtually all synthetic organic compounds, including plastics and pharmaceuticals. Natural gas is consumed almost exclusively as fuel. Coal is used as a fuel and as a reducing agent in metallurgy.
A small fraction of hydrocarbon found on earth, and all currently known hydrocarbon found on other planets and moons, is thought to be abiological.[13]
Hydrocarbons such as ethylene, isoprene, and monoterpenes are emitted by living vegetation.[14]
Some hydrocarbons also are widespread and abundant in the Solar System. Lakes of liquid methane and ethane have been found on Titan, Saturn's largest moon, as confirmed by the Cassini–Huygens space probe.[15] Hydrocarbons are also abundant in nebulae forming polycyclic aromatic hydrocarbon compounds.[16]
Environmental impact
Burning hydrocarbons as fuel, which produces
When soil is contaminated by hydrocarbons, it can have a significant impact on its microbiological, chemical, and physical properties. This can serve to prevent, slow down or even accelerate the growth of vegetation depending on the exact changes that occur. Crude oil and natural gas are the two largest sources of hydrocarbon contamination of soil.[19]
Bioremediation
Bioremediation of hydrocarbon from soil or water contaminated is a formidable challenge because of the chemical inertness that characterize hydrocarbons (hence they survived millions of years in the source rock). Nonetheless, many strategies have been devised, bioremediation being prominent. The basic problem with bioremediation is the paucity of enzymes that act on them. Nonetheless, the area has received regular attention.[20] Bacteria in the gabbroic layer of the ocean's crust can degrade hydrocarbons; but the extreme environment makes research difficult.[21] Other bacteria such as Lutibacterium anuloederans can also degrade hydrocarbons.[22] Mycoremediation or breaking down of hydrocarbon by mycelium and mushrooms is possible.[23][24]
Safety
Hydrocarbons are generally of low toxicity, hence the widespread use of gasoline and related volatile products. Aromatic compounds such as benzene and toluene are narcotic and chronic toxins, and benzene in particular is known to be carcinogenic. Certain rare polycyclic aromatic compounds are carcinogenic. Hydrocarbons are highly
See also
References
- ^ ISBN 0-07-310169-9.
- OCLC 288470227.
- ^ Barnes, I. "TROPOSPHERIC CHEMISTRY AND COMPOSITION (Aromatic Hydrocarbons)". Retrieved 26 October 2020.
- ^ "Benzene global market volume 2015-2026". Statista. Retrieved 5 December 2021.
- (PDF) from the original on 26 September 2015.
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- PMID 28681302.
- ^ "Generating Electricity". Canadian Electricity Association. Retrieved 5 December 2021.
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- ISBN 979-8353989172
- ISBN 0-19-850346-6, p. 21.
- ISBN 0-495-11837-0. pp. 75–81.
- .
- ^ Dewulf, Jo. "Hydrocarbons in the Atmosphere" (PDF). Retrieved 26 October 2020.
- ^ NASA's Cassini Spacecraft Reveals Clues About Saturn Moon. Archived 2 September 2014 at the Wayback Machine. NASA (12 December 2013).
- S2CID 118540862.
- ^ "Microbial Degradation of Alkanes (PDF Download Available)". ResearchGate. Archived from the original on 24 February 2017. Retrieved 23 February 2017.
- ISSN 2073-4395.
- ISBN 978-0-429-07804-0
- PMID 27267117.
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- PMID 17493798.
- ^ Stamets, Paul (2008). "6 ways mushrooms can save the world" (video). TED Talk. Archived from the original on 31 October 2014.
- ISBN 9781580085793.