Limonene

Limonene

Limonene (R)-isomer
Limonene extracted from orange peel
Names
Pronunciation	/ˈlɪmənˌiːn/ LIM-uh-neen
Preferred IUPAC name 1-Methyl-4-(prop-1-en-2-yl)cyclohex-1-ene
Other names 1-Methyl-4-(1-methylethenyl)cyclohexene 4-Isopropenyl-1-methylcyclohexene p-Menth-1,8-diene Racemic: DL-Limonene; Dipentene
Identifiers
CAS Number	138-86-3 (R/S) Y 5989-27-5 (R) Y 5989-54-8 (S) Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:15384 Y
ChEMBL	ChEMBL449062 (R) Y
ChemSpider	20939 (R/S) Y 388386 (S) Y 389747 (R) Y
ECHA InfoCard	100.004.856
KEGG	D00194 Y
PubChem CID	22311 (R/S) 439250 (S)
UNII	9MC3I34447 (R/S) Y GFD7C86Q1W (R) Y 47MAJ1Y2NE (S) Y
CompTox Dashboard (EPA)	DTXSID2029612
SMILES CC1=CCC(CC1)C(=C)C
Properties
Chemical formula	C10H16
Molar mass	136.24 g·mol−1
Appearance	colorless 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)
Solubility in water	Insoluble
Solubility	Miscible with benzene, chloroform, ether, CS2, and oils soluble in CCl4
Chiral rotation ([α]D)	87–102°
Refractive index (nD)	1.4727
Thermochemistry
Std enthalpy of combustion ΔcHo298	−6.128 MJ mol−1
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Skin sensitizer / Contact dermatitis – After aspiration, pulmonary oedema, pneumonitis, and death
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H226, H304, H315, H317, H410
Precautionary statements	P210, P233, P235, P240, P241, P242, P243, P261, P264, P272, P273, P280, P301+P330+P331, P302+P352, P303+P361+P353, P304+P340, P312, P333+P313, P362, P370+P378, P391, P403+P233, P405, P501
NFPA 704 (fire diamond)	2 2 0
Flash point	50 °C (122 °F; 323 K)
Autoignition temperature	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).
Infobox references

Limonene is an organic compound. It is one of the most common monoterpenes. It is used as a food additive and as a

Structure

Limonene is a chiral molecule with two stereoisomers, (R)-limonene and (S)-limonene. Both of them are found in nature, but the (R) isomer is more common.

Occurrence and production

(R)-Limonene is found in the peel of citrus fruits like oranges and lemons. Up to 95% of citrus essential oil is made of limonene. The pure chemical is made by steam distillation of citrus peel or essential oil. Most limonene is produced as a byproduct of the orange juice industry.

(S)-Limonene is sometimes incorrectly associated with lemons, and claimed to be the cause for the different scents of lemons and oranges. In reality, both oranges and lemons contain (R)-limonene. The (S) enantiomer is found some spices like caraway, dill, and bergamot.

Biosynthesis

Limonene is one of many natural terpenes made from geranyl pyrophosphate.

The two stereoisomers of limonene are made by separate enzymes, (R)-limonene synthase and (4S)-limonene synthase.

Sources

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