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Limonene is a colorless liquid hydrocarbon classified as a cyclic terpene. The more common d-isomer possesses a strong smell of oranges.[1] It is used in chemical synthesis as a precursor to carvone and as a renewables-based solvent in cleaning products. The less common l-isomer is found in mint oils and has a piney, turpentine-like odor.

Limonene
Skeletal structure of the R-isomer
Ball-and-stick model of the R-isomer
Limonene extracted from orange peels.
Names
IUPAC name
1-Methyl-4-(1-methylethenyl)-cyclohexene
Other names
4-Isopropenyl-1-methylcyclohexene
p-Menth-1,8-diene
Racemic: DL-limonene; Dipentene
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.025.284
KEGG
UNII
Properties
C10H16
Molar mass 136.24 g·mol−1
Appearance colorless to pale-yellow liquid
Odor Orange
Density 0.8411 g/cm3
Melting point −74.35 °C (−101.83 °F; 198.80 K)
Boiling point 176 °C (349 °F; 449 K)
insoluble
Solubility miscible in alcohol, benzene, chloroform, ether, CS2, and oils
soluble in CCl4
87° - 102°
1.4727
Thermochemistry
−6.128 MJ mol−1
Hazards
R-phrases (outdated) R10 R38 R43 R50/53
S-phrases (outdated) (S2) S24 S37 S60 S61
NFPA 704
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g., diesel fuelHealth code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentineReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogenSpecial hazards (white): no codeNFPA 704 four-colored diamond
Flash point 50 °C (122 °F; 323 K)
237 °C (459 °F; 510 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
Infobox references

Limonene takes its name from the lemon, as the rind of the lemon, like other citrus fruits, contains considerable amounts of this compound, which contributes to their odor. Limonene is a chiral molecule, and biological sources produce one enantiomer: the principal industrial source, citrus fruit, contains d-limonene ((+)-limonene), which is the (R)-enantiomer. Racemic limonene is known as dipentene.[2] d-Limonene is obtained commercially from citrus fruits through two primary methods: centrifugal separation or steam distillation.

Contents

Chemical reactionsEdit

Limonene is a relatively stable terpene and can be distilled without decomposition, although at elevated temperatures it cracks to form isoprene.[3] It oxidizes easily in moist air to produce carveol, carvone, and limonene oxide.[4] With sulfur, it undergoes dehydrogenation to p-cymene.[5]

Limonene occurs commonly as the d or (R)-enantiomer, but racemizes to dipentene at 300 °C. When warmed with mineral acid, limonene isomerizes to the conjugated diene α-terpinene (which can also easily be converted to p-cymene). Evidence for this isomerization includes the formation of Diels-Alder adducts between α-terpinene adducts and maleic anhydride.

It is possible to effect reaction at one of the double bonds selectively. Anhydrous hydrogen chloride reacts preferentially at the disubstituted alkene, whereas epoxidation with mCPBA occurs at the trisubstituted alkene.

In another synthetic method Markovnikov addition of trifluoroacetic acid followed by hydrolysis of the acetate gives terpineol.

BiosynthesisEdit

Limonene is formed from geranyl pyrophosphate, via cyclization of a neryl carbocation or its equivalent as shown.[6] The final step involves loss of a proton from the cation to form the alkene.

The most widely practiced conversion of limonene is to carvone. The three step reaction begins with the regioselective addition of nitrosyl chloride across the trisubstituted double bond. This species is then converted to the oxime with base, and the hydroxylamine is removed to give the ketone-containing carvone.[1]

Safety and researchEdit

d-Limonene applied to skin may cause irritation, but otherwise appears to be safe for human uses.[7]

The enantiomers of perillyl alcohol have been investigated for their potential activities as chemotherapeutic agents,[8] but there is no evidence for efficacy or regulatory approval for such clinical application as of 2017.[9]

UsesEdit

Limonene is common in cosmetic products. As the main odor constituent of citrus (plant family Rutaceae), d-limonene is used in food manufacturing and some medicines, e.g. as a flavoring to mask the bitter taste of alkaloids, and as a fragrance in perfumery, aftershave lotions, bath products and other such products that include fragrance;[10] it is also used as botanical insecticide,[11] the d enantiomer is most active as an insecticide. It is added to cleaning products such as hand cleansers to give a lemon-orange fragrance (see orange oil) and because of its ability to dissolve oils. In contrast, l-limonene has a piney, turpentine-like odor.

In natural and alternative medicine, d-limonene is marketed to relieve gastroesophageal reflux disease and heartburn.[12]

Limonene is increasingly being used as a solvent for cleaning purposes, such as the removal of oil from machine parts, as it is produced from a renewable source (citrus oil, as a byproduct of orange juice manufacture). It is used as a paint stripper and is also useful as a fragrant alternative to turpentine. Limonene is also used as a solvent in some model airplane glues and as a constituent in some paints. All-natural commercial air fresheners, with air propellants, containing limonene are used by philatelists to remove self-adhesive postage stamps from envelope paper.[13]

Limonene is also finding increased use as a solvent for filament-fused 3D printing.[14] Printers can print the plastic of choice for the model, but erect supports and binders from HIPS, a polystyrene plastic that is easily soluble in limonene.

As it is combustible, limonene has also been considered as a biofuel.[15] Reaction Motors, Inc. also tried d-limonene as a rocket fuel. "[A]ll during the runs the test area was blanketed with a delightful odor of lemon oil."[16]

In preparing tissues for histology or histopathology, d-limonene is often used as a less toxic substitute for xylene when clearing dehydrated specimens. Clearing agents are liquids miscible with alcohols (such as ethanol or isopropanol) and with melted paraffin wax, in which specimens are embedded to facilitate cutting of thin sections for microscopy.[17][18][19]

d-Limonene is used in the organic herbicide "Avenger."[20]

Compendial statusEdit

See alsoEdit

ReferencesEdit

  1. ^ a b Fahlbusch, Karl-Georg; Hammerschmidt, Franz-Josef; Panten, Johannes; Pickenhagen, Wilhelm; Schatkowski, Dietmar; Bauer, Kurt; Garbe, Dorothea; Surburg, Horst (2003). "Flavors and Fragrances". Ullmann's Encyclopedia of Industrial Chemistry. ISBN 978-3-527-30673-2. doi:10.1002/14356007.a11_141. 
  2. ^ J. L. Simonsen (1947). The Terpenes. 1 (2nd ed.). Cambridge University Press. OCLC 477048261. [page needed]
  3. ^ Pakdel, H (2001). "Production of dl-limonene by vacuum pyrolysis of used tires". Journal of Analytical and Applied Pyrolysis. 57: 91–107. doi:10.1016/S0165-2370(00)00136-4. 
  4. ^ Karlberg, Ann-Therese; Magnusson, Kerstin; Nilsson, Ulrika (1992). "Air oxidation of d-limonene (the citrus solvent) creates potent allergens". Contact Dermatitis. 26 (5): 332–40. PMID 1395597. doi:10.1111/j.1600-0536.1992.tb00129.x. 
  5. ^ Weitkamp, A. W. (1959). "I. The Action of Sulfur on Terpenes. The Limonene Sulfides". Journal of the American Chemical Society. 81 (13): 3430–3434. doi:10.1021/ja01522a069. 
  6. ^ Mann, J. C.; Hobbs, J. B.; Banthorpe, D. V.; Harborne, J. B. (1994). Natural products: their chemistry and biological significance. Harlow, Essex, England: Longman Scientific & Technical. pp. 308–9. ISBN 0-582-06009-5. 
  7. ^ Kim, Y. W.; Kim, M. J.; Chung, B. Y.; Bang Du, Y; Lim, S. K.; Choi, S. M.; Lim, D. S.; Cho, M. C.; Yoon, K; Kim, H. S.; Kim, K. B.; Kim, Y. S.; Kwack, S. J.; Lee, B. M. (2013). "Safety evaluation and risk assessment of d-Limonene". Journal of Toxicology and Environmental Health, Part B. 16 (1): 17–38. PMID 23573938. doi:10.1080/10937404.2013.769418. 
  8. ^ da Fonseca, CO; et al. (2011). "Efficacy of monoterpene perillyl alcohol upon survival rate of patients with recurrent glioblastoma.". J Cancer Res Clin Oncol. 137 (2): 287–93. PMID 20401670. doi:10.1007/s00432-010-0873-0. 
  9. ^ "Perillyl Alcohol". Memorial Sloan Kettering Cancer Center. 2017. Retrieved 22 February 2017. 
  10. ^ "Limonene". cosmeticsinfo.org. 
  11. ^ EPA R.E.D. Fact Sheet on Limonene, September 1994
  12. ^ Sun, J (2007). "d-Limonene: safety and clinical applications". Alternative Medicine Review. 12 (3): 259–64. PMID 18072821. 
  13. ^ Butler, Peter (October 2010). "It's Like Magic; Removing Self-Adhesive Stamps from Paper" (PDF). American Philatelist. American Philatelic Society. 124 (10): 910–13. 
  14. ^ "Using D-Limonene to Dissolve 3D Printing Support Structures". Fargo 3D Printing. April 26, 2014. Retrieved December 30, 2015. 
  15. ^ Cyclone Power to Showcase External Combustion Engine at SAE Event, Green Car Congress, 20 September 2007
  16. ^ Clark, John D. Ignition!: An Informal History of Liquid Rocket Propellants. Rutgers University Press, 1972. JSTOR, www.jstor.org/stable/j.ctt189ttdk.
  17. ^ Wynnchuk, Maria (1994). "Evaluation of Xylene Substitutes For A Paraffin Tissue Processing". Journal of Histotechnology (2): 143–9. doi:10.1179/014788894794710913. 
  18. ^ Carson F 1997 Histotechnology. A Self-Instructional Text. Chicago: ASCP Press, pp.28-31. ISBN 0-89189-411-X.
  19. ^ Kiernan JA 2008 Histological and Histochemical Methods. 4th ed. Bloxham, UK, pp.54,57. ISBN 978-1-904842-42-2.
  20. ^ Avenger Material Safety Data Sheet http://nebula.wsimg.com/07de45c0af774ba73e06362ad1a56f06?AccessKeyId=C67FD801C8FC93742D64&disposition=0&alloworigin=1
  21. ^ The British Pharmacopoeia Secretariat (2009). "Index, BP 2009" (PDF). Archived from the original (PDF) on 11 April 2009. Retrieved 31 March 2010. 

External linksEdit