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But-2-ene

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But-2-ene
cis
trans
cis
trans
Names
Preferred IUPAC name But-2-ene
Other names β-Butylene
Identifiers
CAS Number
3D model (JSmol)
Beilstein Reference 1718755 1361341
ChEBI
ChemSpider
ECHA InfoCard 100.003.140 Edit this at Wikidata
EC Number
  • 203-452-9
Gmelin Reference 25196 1140 1141
PubChem CID
RTECS number
  • EM2932000 1718756
UNII
CompTox Dashboard (EPA)
InChI
  • InChI=1S/C4H8/c1-3-4-2/h3-4H,1-2H3Key: IAQRGUVFOMOMEM-UHFFFAOYSA-N
  • InChI=1/C4H8/c1-3-4-2/h3-4H,1-2H3Key: IAQRGUVFOMOMEM-UHFFFAOYAW
  • (cis): InChI=1S/C4H8/c1-3-4-2/h3-4H,1-2H3/b4-3-Key: IAQRGUVFOMOMEM-ARJAWSKDSA-N
  • (trans): InChI=1S/C4H8/c1-3-4-2/h3-4H,1-2H3/b4-3+Key: IAQRGUVFOMOMEM-ONEGZZNKSA-N
SMILES
  • C(=CC)C
  • (cis): C/C=C\C
  • (trans): C/C=C/C
Properties
Chemical formula C4H8
Molar mass 56.106 g/mol
Density 0.641 g/ml (cis, 3.7 °C)
0.626 g/ml (trans, 0.9 °C)
Melting point −138.9 °C (−218.0 °F; 134.2 K) (cis)
-105.5 °C (trans)
Boiling point 0.8 to 3.7 °C (33.4 to 38.7 °F; 273.9 to 276.8 K) (Z = 3.7 °C)
(E = 0.8 °C)
Magnetic susceptibility (χ)
  • -42.6·10 cm/mol (cis)
  • -43.3·10 cm/mol (trans)
Hazards
GHS labelling:
Pictograms Flam. Gas 1Press. Gas
Signal word Danger
Hazard statements H220
Precautionary statements P210, P377, P381, P403
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g. propaneInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1 4 0
Flash point −72 °C (−98 °F; 201 K)
Autoignition
temperature 		325 °C (617 °F; 598 K)
Related compounds
Related butenes 1-Butene
cis-2-Butene
trans-2-Butene
Isobutene
Related compounds Butane
Butyne
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). ☒N verify (what is  ?) Infobox references
Chemical compound

But-2-ene is an acyclic alkene with four carbon atoms. It is the simplest alkene exhibiting cis/trans-isomerism (also known as (E/Z)-isomerism); that is, it exists as two geometric isomers cis-but-2-ene ((Z)-but-2-ene) and trans-but-2-ene ((E)-but-2-ene).

It is a petrochemical, produced by the catalytic cracking of crude oil or the dimerization of ethylene. Its main uses are in the production of high-octane gasoline (petrol) on alkylation units and butadiene, although some but-2-ene is also used to produce the solvent butanone via hydration reaction to butan-2-ol followed by oxidation.

The two isomers are extremely difficult to separate by distillation because of the proximity of their boiling points (~4 °C for cis and ~1 °C for trans). However, separation is unnecessary in most industrial settings, as both isomers behave similarly in most of the desired reactions. A typical industrial but-2-ene mixture is 70% (Z)-but-2-ene (cis-isomer) and 30% (E)-but-2-ene (trans-isomer). Butane and but-1-ene are common impurities, present at 1% or more in industrial mixtures, which also contain smaller amounts of isobutene, butadiene and butyne.

References

  1. ^ Record in the GESTIS Substance Database of the Institute for Occupational Safety and Health
  2. ^ Record in the GESTIS Substance Database of the Institute for Occupational Safety and Health
  3. cis-2-Butene, International Chemical Safety Card 0397, Geneva: International Programme on Chemical Safety, March 1996. trans-2-Butene, International Chemical Safety Card 0398, Geneva: International Programme on Chemical Safety, March 1996.
  4. ^ 2-Butene (PDF), SIDS Initial Assessment Report, Geneva: United Nations Environment Programme, February 1995.
  5. Chemical Safety Information from Intergovernmental Organizations Archived December 9, 2009, at the Wayback Machine

External links

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