citronellol
{{Use dmy dates|date=March 2021}}
{{Short description|Pair of enantiomers}}
{{distinguish|Citronellal}}
{{chembox
| Watchedfields = changed
| verifiedrevid = 443528686
| Name = Citronellol
| ImageFile = Citronellol enantiomers.svg
| ImageSize = 250px
| ImageAlt = Skeletal formula of (+)-citronellol and (−)-citronellol
| ImageCaption = (+)-Citronellol (left) and (−)-citronellol (right)
| ImageFile1 = (+)-Citronellol 3D ball.png
| ImageAlt1 = Ball-and-stick model of the (+)-citronellol molecule
| ImageCaption1 = R-(+)-Citronellol
| ImageFile2 = (-)-Citronellol 3D ball.png
| ImageAlt2 = Ball-and-stick model of the (−)-citronellol molecule
| ImageCaption2 = S-(−)-Citronellol
| IUPACName = 3,7-Dimethyloct-6-en-1-ol
| OtherNames = (±)-β-Citronellol; Cephrol, Corol
| Section1 = {{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 13850135
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 565OK72VNF
| UNII1_Ref = {{fdacite|correct|FDA}}
| UNII1 = P01OUT964K
| UNII1_Comment = (R)
| UNII2_Ref = {{fdacite|correct|FDA}}
| UNII2 = 8RSY5Y5658
| UNII2_Comment = (S)
| KEGG_Ref = {{keggcite|correct|kegg}}
| KEGG = C09849
| InChI = 1/C10H20O/c1-9(2)5-4-6-10(3)7-8-11/h5,10-11H,4,6-8H2,1-3H3/t10-/m1/s1
| InChIKey = QMVPMAAFGQKVCJ-SNVBAGLBBU
| InChI1 = 1/C10H20O/c1-9(2)5-4-6-10(3)7-8-11/h5,10-11H,4,6-8H2,1-3H3
| InChIKey1 = QMVPMAAFGQKVCJ-UHFFFAOYAO
| SMILES1 = C\C(C)=C\CCC(C)CCO
| ChEMBL_Ref = {{ebicite|correct|EBI}}
| ChEMBL = 395827
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/C10H20O/c1-9(2)5-4-6-10(3)7-8-11/h5,10-11H,4,6-8H2,1-3H3
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = QMVPMAAFGQKVCJ-UHFFFAOYSA-N
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 106-22-9
| CASNo1_Ref = {{cascite|correct|CAS}}
| CASNo1 = 1117-61-9
| CASNo1_Comment =(R)
| CASNo2_Ref = {{cascite|correct|CAS}}
| CASNo2 = 7540-51-4
| CASNo2_Comment =(S)
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 50462
| PubChem = 8842
| EC_number = 247-737-6
| Beilstein = 1362474
| SMILES = OCC[C@@H](CC/C=C(/C)C)C
}}
| Section2 = {{Chembox Properties
| C=10|H=20|O=1
| Density = 0.855 g/cm3
| BoilingPtC = 225
| Viscosity = 11.1 mPa s
}}
| Section3 = {{Chembox Hazards
| NFPA-H = 1
| NFPA-F = 2
| NFPA-R = 0
| GHSPictograms = {{GHS07}}{{GHS09}}
| GHSSignalWord = Warning
| HPhrases = {{H-phrases|315|317|319}}
| PPhrases = {{P-phrases|261|264|272|273|280|302+352|305+351+338|321|332+313|333+313|337+313|362|363|391|501}}
}}
}}
Citronellol, or dihydrogeraniol, is a natural acyclic monoterpenoid. Both enantiomers occur in nature. (+)-Citronellol, which is found in citronella oils, including Cymbopogon nardus (50%), is the more common isomer. (−)-Citronellol is widespread, but particularly abundant in the oils of rose (18–55%) and Pelargonium geraniums.{{cite book | last= Lawless |first=J. | title = The Illustrated Encyclopedia of Essential Oils | isbn = 978-1-85230-661-8| year = 1995 }}
Preparation
Several million kilograms of citronellol are produced annually. It is mainly obtained by partial hydrogenation of geraniol or nerol over copper chromite catalyst.{{cite book |doi=10.1002/0471238961.2005181602120504.a01.pub2|chapter=Terpenoids |title=Kirk-Othmer Encyclopedia of Chemical Technology |year=2006 |last1=Sell |first1=Charles S. |isbn=0471238961 }} Hydrogenation of both C=C bonds using a nickel catalyst gives tetrahydrogeraniol, yet another commercial fragrance.{{cite book |doi=10.1002/14356007.t11_t01 |chapter=Flavors and Fragrances, 2. Aliphatic Compounds |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2015 |last1=Panten |first1=Johannes |last2=Surburg |first2=Horst |pages=1–55 |isbn=978-3-527-30673-2 }}
Homogeneous catalysts have been investigated for the production of enantiomers.{{cite book | first= Robert H. |last=Morris | chapter = Ruthenium and Osmium | title = The Handbook of Homogeneous Hydrogenation | editor1-first = J. G. |editor1-last=De Vries |editor2-first= C. J. |editor2-last=Elsevier | year = 2007 | publisher = Wiley-VCH | location = Weinheim | isbn = 978-3-527-31161-3}}{{Cite journal | doi = 10.1016/0957-4166(95)00015-H | title = Catalytic Synthesis of (R)- and (S)-citronellol by homogeneous hydrogenation over amidophosphinephosphinite and diaminodiphosphine rhodium complexes | year = 1995 | last1 = Ait Ali | first1 = M. | last2 = Allaoud | first2 = S. | last3 = Karim | first3 = A. | last4 = Roucoux | first4 = A. | last5 = Mortreux | first5 = A. | journal = Tetrahedron: Asymmetry | volume = 6 | issue = 2 | pages = 369}}
Uses
Citronellol is used in perfumes and as a fragrance in cleaning products. In many applications, one of the enantiomers is preferred. It is a component of citronella oil, an insect repellant.
Citronellol is used as a raw material for the production of rose oxide.{{cite journal | title="Dark" Singlet Oxygenation of β-Citronellol: A Key Step in the Manufacture of Rose Oxide | journal=Organic Process Research & Development | doi=10.1021/op900076g | volume=14 | year=2010 | pages=259–262 | last1 = Alsters | first1 = Paul L. | last2 = Jary | first2 = Walther | last3 = Aubry | first3 = Jean-Marie}} It is also a precursor to many commercial and potential fragrances such as citronellol acetate, citronellyl oxyacetaldehyde, citronellyl methyl acetal, and ethyl citronellyl oxalate.
Health and safety
The United States FDA considers citronellol as generally recognized as safe (GRAS) for food use.{{cite web|url=http://www.epa.gov/pesticides/biopesticides/ingredients/factsheets/factsheet_167004.htm|title=Redirect|work=epa.gov|accessdate=29 July 2015}} Citronellol is subject to restrictions on its use in perfumery,{{cite web |url=http://www.ifraorg.org/en-us/standards_restricted/s3/p3 |title=Standards Restricted - IFRA International Fragrance Association |accessdate=19 July 2012 |url-status=dead |archiveurl=https://web.archive.org/web/20120106222844/http://www.ifraorg.org/en-us/standards_restricted/s3/p3 |archivedate=6 January 2012 }} as some people may become sensitised to it, but the degree to which citronellol can cause an allergic reaction in humans is disputed.{{Cite web |url=http://www.leffingwell.com/Cropwatch%20Claims%20Victory%20Over%2026%20Allergens.pdf |title=Cropwatch Report April 2008 |access-date=19 July 2012 |archive-url=https://web.archive.org/web/20140210163144/http://www.leffingwell.com/Cropwatch%20Claims%20Victory%20Over%2026%20Allergens.pdf |archive-date=10 February 2014 |url-status=dead }}[http://www2.mst.dk/common/Udgivramme/Frame.asp?pg=http://www2.mst.dk/udgiv/publications/2006/87-7052-278-2/html/kap07_eng.htm Survey and health assessment of chemical substances in massage oils] {{webarchive|url=https://web.archive.org/web/20070927205013/http://www2.mst.dk/common/Udgivramme/Frame.asp?pg=http%3A%2F%2Fwww2.mst.dk%2Fudgiv%2Fpublications%2F2006%2F87-7052-278-2%2Fhtml%2Fkap07_eng.htm |date=27 September 2007 }}
In terms of dermal safety, citronellol has been evaluated as an insect repellent.{{cite journal | last1= Taylor |first1=W. G. |last2=Schreck |first2=C. E. | title = Chiral-phase capillary gas chromatography and mosquito repellent activity of some oxazolidine derivatives of (+)- and (−)-citronellol | journal = Journal of Pharmaceutical Sciences| year = 1985 | volume = 74 | issue = 5 | pages = 534–539 | doi = 10.1002/jps.2600740508 | pmid = 2862274| url = https://zenodo.org/record/1229253}}