Octane

Octane is a hydrocarbon and an alkane with the chemical formula C8H18, and the condensed structural formula CH3(CH2)6CH3. Octane has many structural isomers that differ by the location of branching in the carbon chain. One of these isomers, 2,2,4-trimethylpentane (commonly called iso-octane), is used as one of the standard values in the octane rating scale.

Octane
Skeletal formula of octane
Skeletal formula of octane with all implicit carbons shown, and all explicit hydrogens added
Ball-and-stick model of octane
Space-filling model of octane
Names
Systematic IUPAC name
Octane[1]
Other names
n-Octane
Identifiers
CAS Number
3D model (JSmol)
3DMet
Beilstein Reference
 1696875
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.003.539
EC Number
  • 203-892-1
Gmelin Reference
 82412
KEGG
MeSH octane
PubChem CID
RTECS number
  • RG8400000
UNII
UN number 1262
InChI
  • InChI=1S/C8H18/c1-3-5-7-8-6-4-2/h3-8H2,1-2H3 checkY
    Key: TVMXDCGIABBOFY-UHFFFAOYSA-N checkY
SMILES
  • CCCCCCCC
Properties
Chemical formula
 CH3(CH2)6CH3
Molar mass 114.232 g·mol−1
Appearance Colourless liquid
Odor Gasoline-like[2]
Density 0.703 g/cm3
Melting point −57.1 to −56.6 °C; −70.9 to −69.8 °F; 216.0 to 216.6 K
Boiling point 125.1 to 126.1 °C; 257.1 to 258.9 °F; 398.2 to 399.2 K
Solubility in water
 0.007 mg/dm3 (at 20 °C)
log P 4.783
Vapor pressure 1.47 kPa (at 20.0 °C)
Henry's law
constant (kH)
 29 nmol/(Pa·kg)
Conjugate acid Octonium
Magnetic susceptibility (χ)
 −96.63·10−6 cm3/mol
Refractive index (nD)
 1.398
Viscosity
  • 0.509 mPa·s (25 °C)[3]
  • 0.542 mPa·s (20 °C)
Thermochemistry
Heat capacity (C)
 255.68 J/(K·mol)
Std molar
entropy (S⦵298)
 361.20 J/(K·mol)
Std enthalpy of
formation (ΔfH⦵298)
 −252.1 to −248.5 kJ/mol
Std enthalpy of
combustion (ΔcH⦵298)
 −5.53 to −5.33 MJ/mol
Hazards
GHS labelling:
Pictograms
 GHS02: Flammable GHS07: Exclamation mark GHS08: Health hazard GHS09: Environmental hazard
Signal word
 Danger
Hazard statements
 H225, H304, H315, H336, H410
Precautionary statements
 P210, P261, P273, P301+P310, P331
NFPA 704 (fire diamond)
NFPA 704 four-colored diamond
1
3
0
Flash point 13.0 °C (55.4 °F; 286.1 K)
Autoignition
temperature
 220.0 °C (428.0 °F; 493.1 K)
Explosive limits 0.96 – 6.5%
Lethal dose or concentration (LD, LC):
428 mg/kg (mouse, intravenous)[4]
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 500 ppm (2350 mg/m3)[2]
REL (Recommended)
 TWA 75 ppm (350 mg/m3) C 385 ppm (1800 mg/m3) [15-minute][2]
IDLH (Immediate danger)
 1000 ppm[2]
Related compounds
Related alkanes
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Octane is a component of gasoline and petroleum. Under standard temperature and pressure, octane is an odorless, colorless liquid. Like other short-chained alkanes with a low molecular weight, it is volatile, flammable, and toxic. For examples, as a neurotoxin with narcotic effects, n-octane is almost twice times as toxic as n-heptane.[5]

Isomers

N-octane has 23 constitutional isomers. 8 of these isomers have one stereocenter; 3 of them have two stereocenters.

(3S,4S)-3,4-Dimethylhexane (top left) and (3R,4R)-3,4-Dimethylhexane (top right) are non-superimposable mirror images, so they are chiral enantiomers. (meso)-3,4-Dimethylhexane (bottom) has a superimposable mirror image, so it is an achiral meso compound.

Achiral Isomers:

  • 2-Methylheptane
  • 4-Methylheptane
  • 3-Ethylhexane
  • 2,2-Dimethylhexane
  • 2,5-Dimethylhexane
  • (meso)-3,4-Dimethylhexane
  • 3,3-Dimethylhexane
  • 3-Ethyl-2-methylpentane
  • 3-Ethyl-3-methylpentane
  • 2,2,4-Trimethylpentane (i.e. iso-octane)
  • 2,3,3-Trimethylpentane
  • 2,3,4-Trimethylpentane
  • 2,2,3,3-Tetramethylbutane

Chiral Isomers:

  • (3R)-3-Methylheptane
  • (3S)-3-Methylheptane
  • (3R)-2,3-Dimethylhexane
  • (3S)-2,3-Dimethylhexane
  • (4R)-2,4-Dimethylhexane
  • (4S)-2,4-Dimethylhexane
  • (3R,4R)-3,4-Dimethylhexane
  • (3S,4S)-3,4-Dimethylhexane
  • (3R)-2,2,3-Trimethylpentane
  • (3S)-2,2,3-Trimethylpentane

Production and se

In petrochemistry, octanes are not typically differentiated or purified as specific compounds. Octanes are components of particular boiling fractions.[6]

A common route to such fractions is the alkylation reaction between iso-butane and 1-butene, which forms iso-octane.[7]

Octane is commonly used as a solvent in paints and adhesives.

Metabolism

Octanes are not produced biologically.

N-octane is the octane isomer that has the longest carbon skeleton. Unlike its constitutional isomers, it has a very low knock resistance.
The octane isomer, iso-octane, is used as one of the standards for octane ratings. It has a rating of 100 by definition.
The octane isomer 2,3,3-Trimethylpentane has an octane rating exceeding 100.

References
  1. "octane - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 16 September 2004. Identification and Related Records. Retrieved 6 January 2012.
  2. NIOSH Pocket Guide to Chemical Hazards. "#0470". National Institute for Occupational Safety and Health (NIOSH).
  3. Dymond, J. H.; Oye, H. A. (1994). "Viscosity of Selected Liquid n-Alkanes". Journal of Physical and Chemical Reference Data. 23 (1): 41–53. Bibcode:1994JPCRD..23...41D. doi:10.1063/1.555943. ISSN 0047-2689.
  4. "Octane". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  5. "1988 OSHA PEL Project - Octane | NIOSH | CDC". www.cdc.gov. 2020-02-27. Retrieved 2024-04-19.
  6. "Fractionation". www.appliedcontrol.com. Retrieved 2024-04-19.
  7. Ross, Julian (January 1986). "Ullmann's Encyclopedia of industrial chemistry". Applied Catalysis. 27 (2): 403–404. doi:10.1016/s0166-9834(00)82943-7. ISSN 0166-9834.
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