Octane

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Not to be confused with octene or octyne.
For the gasoline rating system, see Octane rating. For other uses, see Octane (disambiguation).
Octane
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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
3D model (JSmol)
1696875
ChEBI
ChEMBL
ChemSpider
DrugBank
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EC Number
  • 203-892-1
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82412
KEGG
MeSH octane
RTECS number
  • RG8400000
UNII
UN number 1262
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  • InChI=1S/C8H18/c1-3-5-7-8-6-4-2/h3-8H2,1-2H3 checkY
    Key: TVMXDCGIABBOFY-UHFFFAOYSA-N checkY
  • CCCCCCCC
Properties
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
0.07 mg / 100 g (at 298 K) [3]
log P 4.783
Vapor pressure 1.47 kPa (at 20.0 °C)
29 nmol/(Pa·kg)
Conjugate acid Octonium
−96.63·10−6 cm3/mol
1.398
Viscosity
  • 0.509 mPa·s (25 °C)[4]
  • 0.542 mPa·s (20 °C)
Thermochemistry
255.68 J/(K·mol)
361.20 J/(K·mol)
−252.1 to −248.5 kJ/mol
−5.53 to −5.33 MJ/mol
Hazards
GHS labelling:
GHS02: Flammable GHS07: Exclamation mark GHS08: Health hazard GHS09: Environmental hazard
Danger
H225, H304, H315, H336, H410
P210, P261, P273, P301+P310, P331
NFPA 704 (fire diamond)

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1
3
0
Flash point 13.0 °C (55.4 °F; 286.1 K)
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)[5]
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).

Octane is a hydrocarbon and also 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 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. Octane is 1.2 to 2 times more toxic than heptane.[6]

Isomers

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

File:Octane stereo isomers 10 3 4 dimethylhexane.svg
(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:

Chiral isomers:

Production and use

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In petrochemistry, octanes are not typically differentiated or purified as specific compounds. Octanes are components of particular boiling fractions.[7]

A common route to such fractions is the alkylation reaction between iso-butane and 1-butene, which forms iso-octane.[8]

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

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

References

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  3. ^ https://srdata.nist.gov/solubility/sol_detail.aspx?sysID=38_103
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