Chemical Identity and Composition

4.Chemical Identity and Composition

4.1Chemical identity

Limonene occurs as the d and l isomers, and the racemic mixture dl-limonene known as dipentene. The chemical identities of these chemicals are listed in Table 4.1.

There are some changes in limonene isomer Chemical Abstracts Service (CAS) numbers as follows:

Chemical name	Previous CAS number	Superseded with
d-Limonene	7705-13-7 95327-98-3	5989-27-5
l-Limonene	7721-11-1	5989-54-8
Dipentene	7705-14-8	138-86-3

CAS number	Chemical name#
68647-72-3	Terpenes and terpenoids, orange oil
68917-57-7	Terpenes and terpenoids, mixed sour and sweet orange oil
68917-58-8	Terpenes and terpenoids, mixed grapefruit oil and shaddock oil
65996-99-8	Terpenes and terpenoids, turpentine oil, limonene fraction
68956-56-9	Hydrocarbons, terpene processing by product
8024-48-6	Orange, sweet, extract

Chemical Identity	d-Limonene	l-Limonene	Dipentene
CAS No.:	5989-27-5	5989-54-8	138-86-3
IUPAC Name:	(R)-(+)-para-Mentha-1,8-diene	(S)-(-)-para-Mentha-1,8-diene	()-para-Mentha-1,8-diene
EINECS No.:	227-813-5	227-815-6	205-341-0
Molecular Formula:	C10H16	C10H16	C10H16
Structural Formula:	CH3-C6C8-C(CH3)=CH2	CH3-C6C8-C(CH3)=CH2	CH3-C6C8-C(CH3)=CH2
Molecular Weight:	136.24	136.24	136.24
Synonyms:	FEMA 2633 (+)-4-Isopropenyl-1-methyl-1-cyclohexene d-(+)-Limonene (+)-(R)-Limonene d-p-Mentha-1,8-diene p-Mentha-1,8-diene (R)-1-methyl-4-(1-methylethenyl)-cyclohexene NCI-C55572	(-)-Limonene 1-methyl-4-(1-methylethenyl)-(s)-cyclohexene	Acintene DP Acintene DP dipentene Cajeputene Cinene Dipanol Inactive limonene Kautschin Limonene dl-limonene 1, 8(9)-p-Menthadiene 1-methyl-4-isopropenyl-1-cyclohexene Nesol -1,8-Terpodiene Unitene
Other Names:	Citrus terpenes Orange terpenes Menthadiene Terpene hydrocarbons 1,4-(8)-p-menthadiene Orange oil terpenes Cajeputene	None	None

5.Physical and Chemical Properties

5.1Physical state

Limonene is a colourless liquid with a characteristic citrus odour at room temperature.

5.2Physical properties

Physical properties of limonene are presented in Table 5.1. The values cited are from the IPCS report (1998) unless otherwise stated.

Table 5.1 - Physical properties

Property	d-Limonene	l-Limonene	Dipentene
Boiling point (C)	175.5-176.0	175.5	176.0
Melting point (C)	-74.35 -96.9*	-74.35	-95.9
Density (g/cm3 at 20C)	0.8411	0.8422	0.8402
Relative density (water = 1)	0.84#	0.84#	0.84#
Water solubility (mg/L at 25C)	13.8	-	-
Vapour pressure	0.19 kPa at 20C	0.19 kPa at 20C	0.19 kPa at 20C
Relative vapour density (air = 1)	4.7*	-	4.7 +
Henry’s law constant (kPa m3/mol at 25C)	34.8	-	-
Partition coefficient (Log Kow)	4.23	-	4.83 4.23+
Lower flammable limit	0.7%#	0.7%#	0.7%#
Upper flammable limit	6.1%#	6.1%#	6.1%#
Autoignition temperature (C)	237#	237#	237#
Flash point (C)	48 (closed cup) #	48 (closed cup) #	45 (closed cup) # 48 (open cup)@

* IARC (1999), ^# Canadian Centre for Occupational Health and Safety (2001), ⁺ HSDB (accessed 2001), ^@ Gangolli (1999).

The vapour pressures of limonenes are not high, but the rate of vaporization of limonene in the environment may be high due to the low solubility in water and high value of Henry’s law constant. Limonenes have been measured as volatile organic chemicals (VOCs).

Limonene is a flammable liquid. Explosive vapour/air mixtures may be formed at temperatures above 48C (IPCS, 1998). Limonene liquid can float on water and may possibly travel to distant locations and/or spread fire. Mixtures of limonene vapour and air at concentrations in the flammable range may be ignited by a static spark as static charge may be accumulated by flow or agitation. (CCOHS, 2001).

Rags or other combustible material that have been wet or soaked with limonene may spontaneously combust. Peroxides formed by oxidation may be hazardous for explosion if they become highly concentrated through distillation.

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