# Isoprene

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"Isoprenyl" redirects here. Not to be confused with [isopropenyl](/source/Isopropenyl).

**Isoprene**, or **2-methyl-1,3-butadiene**, is a common [volatile organic compound](/source/Volatile_organic_compound) with the formula CH2=C(CH3)−CH=CH2. In its pure form it is a colorless volatile liquid. It is produced by many plants and animals[1] (including humans) and its polymers are the main component of [natural rubber](/source/Natural_rubber).

## History and etymology

[Charles Greville Williams](/source/Charles_Greville_Williams) named the compound in 1860 after obtaining it from the [pyrolysis](/source/Pyrolysis) of natural rubber. He correctly deduced the mass shares of carbon and hydrogen[2] (but arrived at an incorrect formula C10H8 because the modern atomic weight of carbon was not adopted until the [Karlsruhe Congress](/source/Karlsruhe_Congress) held later that year). He did not specify the reasons for the name, but it is hypothesized that it came from "[propylene](/source/Propylene)" with which isoprene shares some physical and chemical properties. The first one to observe recombination of isoprene into rubber-like substance was [Gustave Bouchardat](/source/Gustave_Bouchardat) in 1879, and [William A. Tilden](/source/William_A._Tilden) identified its structure five years later.[3]

## Natural occurrences

Isoprene is produced and emitted by many species of trees (major producers are [oaks](/source/Oak), [poplars](/source/Poplars), [eucalyptus](/source/Eucalyptus), [phytoplankton](/source/Phytoplankton), and some legumes). Yearly production of isoprene emissions by vegetation is around 600 million [metric tons](/source/Metric_ton), half from tropical broadleaf trees and the remainder primarily from [shrubs](/source/Shrub).[4] This is about equivalent to [methane emissions](/source/Methane_emissions) and accounts for around one-third of all [hydrocarbons](/source/Hydrocarbons) released into the atmosphere. In [deciduous](/source/Deciduous) forests, isoprene makes up approximately 80% of hydrocarbon emissions. While their contribution is small compared to trees, microscopic and macroscopic [algae](/source/Algae) also produce isoprene.[5]

### Plants

Isoprene is made through the [methyl-erythritol 4-phosphate pathway](/source/Non-mevalonate_pathway) (MEP pathway, also called the non-[mevalonate pathway](/source/Mevalonate_pathway)) in the [chloroplasts](/source/Chloroplast) of plants. One of the two end-products of MEP pathway, [dimethylallyl pyrophosphate](/source/Dimethylallyl_pyrophosphate) (DMAPP), is cleaved by the enzyme [isoprene synthase](/source/Isoprene_synthase) to form isoprene and diphosphate. Therefore, inhibitors that block the MEP pathway, such as [fosmidomycin](/source/Fosmidomycin), also block isoprene formation. Isoprene emission increases dramatically with temperature and maximizes at around 40 °C. This has led to the hypothesis that isoprene may protect plants against heat stress (thermotolerance hypothesis, see below). Emission of isoprene is also observed in some bacteria and this is thought to come from non-enzymatic degradations from DMAPP. Global emission of isoprene by plants is estimated at around 350 million tons per year.[6]

#### Regulation

Isoprene emission in plants is controlled both by the availability of the substrate (DMAPP) and by [enzyme](/source/Enzyme) (isoprene synthase) activity. In particular, light, CO2 and O2 dependencies of isoprene emission are controlled by substrate availability, whereas temperature dependency of isoprene emission is regulated both by substrate level and enzyme activity.

### In humans and other organisms

Isoprene is the most abundant hydrocarbon measurable in the breath of humans.[7][8][9] The estimated production rate of isoprene in the human body is 0.15 [μmol](/source/Mole_(unit))/(kg·h), equivalent to approximately 17 mg/day for a person weighing 70 kg. Human breath isoprene originates from lipolytic cholesterol metabolism within the skeletal muscular peroxisomes and *IDI2* gene acts as the production determinant.[10] Due to the absence of *IDI2* gene, animals such as pigs and bottle-nose dolphins do not exhale isoprene.

Isoprene is common in low concentrations in many foods. Many species of soil and marine bacteria, such as [Actinomycetota](/source/Actinomycetota), are capable of degrading isoprene and using it as a fuel source.

## Biological roles

Isoprene emission appears to be a mechanism that trees use to combat [abiotic stresses](/source/Abiotic_stress).[11] In particular, isoprene has been shown to protect against moderate heat stress (around 40 °C). It may also protect plants against large fluctuations in leaf temperature. Isoprene is incorporated into and helps stabilize cell membranes in response to heat stress.

Isoprene also confers resistance to reactive oxygen species.[12] The amount of isoprene released from isoprene-emitting vegetation depends on leaf mass, leaf area, light (particularly photosynthetic photon flux density, or PPFD) and leaf temperature. Thus, during the night, little isoprene is emitted from tree leaves, whereas daytime emissions are expected to be substantial during hot and sunny days, up to 25 μg/(g dry-leaf-weight)/hour in many oak species.[13]

### Isoprenoids

The isoprene skeleton can be found in naturally occurring compounds called [terpenes](/source/Terpenes) and [terpenoid](/source/Terpenoid) (oxygenated terpenes), collectively called isoprenoids. These compounds do not arise from isoprene itself. Instead, the precursor to isoprene units in biological systems is [dimethylallyl pyrophosphate](/source/Dimethylallyl_pyrophosphate) (DMAPP) and its isomer [isopentenyl pyrophosphate](/source/Isopentenyl_pyrophosphate) (IPP). The plural 'isoprenes' is sometimes used to refer to [terpenes](/source/Terpene) in general.

Examples of isoprenoids include [carotene](/source/Carotene), [phytol](/source/Phytol), [retinol](/source/Retinol) ([vitamin A](/source/Vitamin_A)), [tocopherol](/source/Tocopherol) ([vitamin E](/source/Vitamin_E)), [dolichols](/source/Dolichol), and [squalene](/source/Squalene). [Heme](/source/Heme) A has an isoprenoid tail, and [lanosterol](/source/Lanosterol), the sterol precursor in animals, is derived from squalene and hence from isoprene. The functional isoprene units in biological systems are [dimethylallyl pyrophosphate](/source/Dimethylallyl_pyrophosphate) (DMAPP) and its isomer [isopentenyl pyrophosphate](/source/Isopentenyl_pyrophosphate) (IPP), which are used in the biosynthesis of naturally occurring isoprenoids such as [carotenoids](/source/Carotenoid), [quinones](/source/Quinone), lanosterol derivatives (e.g. steroids) and the [prenyl](/source/Prenyl) chains of certain compounds (e.g. phytol chain of chlorophyll). Isoprenes are used in the cell membrane monolayer of many [Archaea](/source/Archaea), filling the space between the diglycerol tetraether head groups. This is thought to add structural resistance to harsh environments in which many Archaea are found.

Similarly, [natural rubber](/source/Natural_rubber) is composed of linear [polyisoprene](/source/Polyisoprene) chains of very high [molecular weight](/source/Molecular_weight) and other natural molecules.[14]

## Industrial production

Isoprene is most readily available industrially as a byproduct of the thermal [cracking](/source/Cracking_(chemistry)) of [petroleum naphtha](/source/Petroleum_naphtha) or oil, as a side product in the production of [ethylene](/source/Ethylene). Where thermal cracking of oil is less common, isoprene can be produced by dehydrogenation of [isopentane](/source/Isopentane). Isoprene can be synthesized in two steps from [isobutylene](/source/Isobutylene), starting with a [Prins reaction](/source/Prins_reaction) with [formaldehyde](/source/Formaldehyde) to give [isoprenol](/source/Isoprenol), which is then dehydrated to isoprene:[15]

Where cheap [acetylene](/source/Acetylene) is produced from coal-derived [calcium carbide](/source/Calcium_carbide), it may be combined with [acetone](/source/Acetone) to make 3-methylbutynol which is then hydrogenated and dehydrated to isoprene.[16]

About 800,000 metric tons are produced annually. About 95% of isoprene production is used to produce cis-1,4-polyisoprene—a [synthetic](/source/Synthetic_rubber) version of [natural rubber](/source/Natural_rubber).[14]

Natural rubber consists mainly of poly-cis-isoprene with a molecular mass of 100,000 to 1,000,000 g/mol. Typically natural rubber contains a few percent of other materials, such as proteins, fatty acids, resins, and inorganic materials. Some natural rubber sources, called [gutta percha](/source/Gutta_percha), are composed of trans-1,4-polyisoprene, a structural [isomer](/source/Isomer) that has similar, but not identical, properties.[14]

## See also

- [Natural rubber](/source/Natural_rubber)
- [Neoprene](/source/Neoprene)

## Further reading

- Greville Williams, C. (1860). "On Isoprene and Caoutchine". *Proceedings of the Royal Society of London*. **10**: 516–519. [JSTOR 111688](https://www.jstor.org/stable/111688)

## References

1. Sharkey TD (1996). "Isoprene synthesis by plants and animals". *Endeavour*. **20** (2): 74–8. [doi:10.1016/0160-9327(96)10014-4](https://doi.org/10.1016/0160-9327(96)10014-4). [PMID 8690002](https://pubmed.ncbi.nlm.nih.gov/8690002)

1. Williams CG (1860). ["On isoprene and caoutchine"](https://babel.hathitrust.org/cgi/pt?id=hvd.32044092762079;view=1up;seq=550). *Proceedings of the Royal Society of London*. **10**: 516–519. [doi:10.1098/rspl.1859.0101](https://doi.org/10.1098/rspl.1859.0101). [S2CID 104233421](https://api.semanticscholar.org/CorpusID:104233421)

1. Loadman MJ (2012-12-06). [*Analysis of Rubber and Rubber-like Polymers*](https://books.google.com/books?id=rjD7CAAAQBAJ&pg=PA10). Springer. p. 10. ISBN 978-94-011-4435-3.

1. Guenther A, Karl T, Harley P, Wiedinmyer C, Palmer PI, Geron C (2006). "Estimates of global terrestrial isoprene emissions using MEGAN (Model of Emissions of Gases and Aerosols from Nature)". *Atmospheric Chemistry and Physics*. **6** (11): 3181–3210. [Bibcode:2006ACP.....6.3181G](https://ui.adsabs.harvard.edu/abs/2006ACP.....6.3181G). [doi:10.5194/acp-6-3181-2006](https://doi.org/10.5194/acp-6-3181-2006). [hdl:20.500.11820/429435d3-e131-45e2-8bba-42a3d552cc59](https://hdl.handle.net/20.500.11820/429435d3-e131-45e2-8bba-42a3d552cc59)

1. Johnston A, Crombie AT, El Khawand M, Sims L, Whited GM, McGenity TJ, Colin Murrell J (September 2017). "Identification and characterisation of isoprene-degrading bacteria in an estuarine environment". *Environmental Microbiology*. **19** (9): 3526–3537. [doi:10.1111/1462-2920.13842](https://doi.org/10.1111/1462-2920.13842). [PMC 6849523](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6849523). [PMID 28654185](https://pubmed.ncbi.nlm.nih.gov/28654185)

1. ["Isoprene emissions version 2021"](https://emissions.aeronomie.be/index.php/bottom-up/isoprenev2021). *emissions.aeronomie.be*. Retrieved 2022-09-26.

1. Gelmont D, Stein RA, Mead JF (April 1981). "Isoprene-the main hydrocarbon in human breath". *Biochemical and Biophysical Research Communications*. **99** (4): 1456–60. [doi:10.1016/0006-291X(81)90782-8](https://doi.org/10.1016/0006-291X(81)90782-8). [PMID 7259787](https://pubmed.ncbi.nlm.nih.gov/7259787)

1. King J, Koc H, Unterkofler K, Mochalski P, Kupferthaler A, Teschl G, Teschl S, Hinterhuber H, Amann A (December 2010). "Physiological modeling of isoprene dynamics in exhaled breath". *Journal of Theoretical Biology*. **267** (4): 626–37. [arXiv:1010.2145](https://arxiv.org/abs/1010.2145). [Bibcode:2010JThBi.267..626K](https://ui.adsabs.harvard.edu/abs/2010JThBi.267..626K). [doi:10.1016/j.jtbi.2010.09.028](https://doi.org/10.1016/j.jtbi.2010.09.028). [PMID 20869370](https://pubmed.ncbi.nlm.nih.gov/20869370). [S2CID 10267120](https://api.semanticscholar.org/CorpusID:10267120)

1. Williams J, Stönner C, Wicker J, Krauter N, Derstroff B, Bourtsoukidis E, Klüpfel T, Kramer S (May 2016). "Cinema audiences reproducibly vary the chemical composition of air during films, by broadcasting scene specific emissions on breath". *Scientific Reports*. **6**. [Bibcode:2016NatSR...625464W](https://ui.adsabs.harvard.edu/abs/2016NatSR...625464W). [doi:10.1038/srep25464](https://doi.org/10.1038/srep25464). [PMC 4862009](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4862009). [PMID 27160439](https://pubmed.ncbi.nlm.nih.gov/27160439)

1. Sukul, Pritam; Richter, Anna; Junghanss, Christian; Schubert, Jochen K.; Miekisch, Wolfram (2023-09-30). ["Origin of breath isoprene in humans is revealed via multi-omic investigations"](https://www.nature.com/articles/s42003-023-05384-y). *Communications Biology*. **6** (1): 1–12. [doi:10.1038/s42003-023-05384-y](https://doi.org/10.1038/s42003-023-05384-y). [ISSN 2399-3642](https://www.worldcat.org/issn/2399-3642). [PMC 10542801](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10542801)

1. Sharkey TD, Wiberley AE, Donohue AR (January 2008). "Isoprene emission from plants: why and how". *Annals of Botany*. **101** (1): 5–18. [doi:10.1093/aob/mcm240](https://doi.org/10.1093/aob/mcm240). [PMC 2701830](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2701830). [PMID 17921528](https://pubmed.ncbi.nlm.nih.gov/17921528)

1. Vickers CE, Possell M, Cojocariu CI, Velikova VB, Laothawornkitkul J, Ryan A, Mullineaux PM, Nicholas Hewitt C (May 2009). "Isoprene synthesis protects transgenic tobacco plants from oxidative stress". *Plant, Cell & Environment*. **32** (5): 520–31. [doi:10.1111/j.1365-3040.2009.01946.x](https://doi.org/10.1111/j.1365-3040.2009.01946.x). [PMID 19183288](https://pubmed.ncbi.nlm.nih.gov/19183288)

1. Benjamin MT, Sudol M, Bloch L, Winer AM (1996). "Low-emitting urban forests: A taxonomic methodology for assigning isoprene and monoterpene emission rates". *Atmospheric Environment*. **30** (9): 1437–1452. [Bibcode:1996AtmEn..30.1437B](https://ui.adsabs.harvard.edu/abs/1996AtmEn..30.1437B). [doi:10.1016/1352-2310(95)00439-4](https://doi.org/10.1016/1352-2310(95)00439-4)

1. Greve HH (2000). "Rubber, 2. Natural". *Ullmann's Encyclopedia of Industrial Chemistry*. [doi:10.1002/14356007.a23_225](https://doi.org/10.1002/14356007.a23_225). ISBN 978-3-527-30673-2.

1. Weitz, Hans Martin & Loser, Eckhard (2000). "Isoprene". *Ullmann's Encyclopedia of Industrial Chemistry*. [doi:10.1002/14356007.a14_627](https://doi.org/10.1002/14356007.a14_627). ISBN 3-527-30673-0.

1. ["Isoprene: Properties, Production And Uses"](https://chemcess.com/isoprene-properties-production-and-uses/). 2024-03-25. Retrieved 2024-11-03.

## Further reading

- *The Merck Index*. 11th ed. Rahway NJ. USA: Merck & Co Inc. 1989. ISBN 978-0-911910-28-5.
- Bekkedahl N, Wood LA, Wojciechowski M (1936). "Some physical properties of isoprene". *Journal of Research of the National Bureau of Standards*. **17** (6): 883. [doi:10.6028/jres.017.052](https://doi.org/10.6028/jres.017.052)
- Poisson N, Kanakidou M, Crutzen PJ (2000). "Impact of Non-Methane Hydrocarbons on Tropospheric Chemistry and the Oxidizing Power of the Global Troposphere: 3-Dimensional Modelling Results". *Journal of Atmospheric Chemistry*. **36** (2): 157–230. [Bibcode:2000JAtC...36..157P](https://ui.adsabs.harvard.edu/abs/2000JAtC...36..157P). [doi:10.1023/A:1006300616544](https://doi.org/10.1023/A:1006300616544). [S2CID 94217044](https://api.semanticscholar.org/CorpusID:94217044)
- Claeys M, Graham B, Vas G, Wang W, Vermeylen R, Pashynska V, Cafmeyer J, Guyon P, Andreae MO, Artaxo P, Maenhaut W (February 2004). "Formation of secondary organic aerosols through photooxidation of isoprene". *Science*. **303** (5661): 1173–6. [Bibcode:2004Sci...303.1173C](https://ui.adsabs.harvard.edu/abs/2004Sci...303.1173C). [doi:10.1126/science.1092805](https://doi.org/10.1126/science.1092805). [PMID 14976309](https://pubmed.ncbi.nlm.nih.gov/14976309). [S2CID 19268599](https://api.semanticscholar.org/CorpusID:19268599)
- Pier PA, McDuffie C (1997). "Seasonal isoprene emission rates and model comparisons using whole-tree emissions from white oak". *Journal of Geophysical Research: Atmospheres*. **102** (D20): 23963–23971. [Bibcode:1997JGR...10223963P](https://ui.adsabs.harvard.edu/abs/1997JGR...10223963P). [doi:10.1029/96JD03786](https://doi.org/10.1029/96JD03786)
- Pöschl U, Von Kuhlmann R, Poisson N, Crutzen PJ (2000). "Development and Intercomparison of Condensed Isoprene Oxidation Mechanisms for Global Atmospheric Modeling". *Journal of Atmospheric Chemistry*. **37** (1): 29–52. [Bibcode:2000JAtC...37...29P](https://ui.adsabs.harvard.edu/abs/2000JAtC...37...29P). [doi:10.1023/A:1006391009798](https://doi.org/10.1023/A:1006391009798). [S2CID 93419825](https://api.semanticscholar.org/CorpusID:93419825)
- Monson RK, Holland EA (2001). "Biospheric Trace Gas Fluxes and Their Control over Tropospheric Chemistry". *Annual Review of Ecology and Systematics*. **32**: 547–576. [doi:10.1146/annurev.ecolsys.32.081501.114136](https://doi.org/10.1146/annurev.ecolsys.32.081501.114136)

## External links

- [Report on Carcinogens, Fourteenth Edition; U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program](https://web.archive.org/web/20161115062414/http://ntp.niehs.nih.gov/pubhealth/roc/index-1.html)
- [Science News article describing how isoprene released by plants is converted to light-scattering aerosols](http://www.sciencenews.org/view/generic/id/46200/title/A_source_of_haze) [Archived](https://web.archive.org/web/20110604222657/http://www.sciencenews.org/view/generic/id/46200/title/A_source_of_haze) 2011-06-04 at the Wayback Machine

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Adapted from the Wikipedia article [Isoprene](https://en.wikipedia.org/wiki/Isoprene) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Isoprene?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.