CAS number 107-01-7 YesY
ChemSpider 11719 YesY
UNII S1SK37516R YesY
EC-number 203-452-9
ChEBI CHEBI:48363 YesY
RTECS number EM2932000
Jmol-3D images Image 1
Molecular formula C4H8
Molar mass 56.106 g/mol
Melting point


Boiling point

4 °C, 277 K, 39 °F

GHS pictograms Flam. Gas 1Template:GHS04
GHS signal word DANGER
GHS hazard statements H220
GHS precautionary statements P210, P377, P381, P403
EU Index 601-012-00-4
EU classification Extremely flammable (F+)
R-phrases R12
S-phrases (S2) S9 S16 S33
NFPA 704
NFPA 704.svg
Flash point flammable gas
324 °C (615 °F)
Related compounds
Related butenes 1-Butene
Related compounds Butane
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

2-Butene 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 geometrical isomers cis-2-butene ((Z)-2-butene), shown at the right, and trans-2-butene ((E)-2-butene), not shown.

It is a petrochemical, produced by the catalytic cracking of crude oil. Its main uses are in the production of gasoline (petrol) and butadiene,[2] although some 2-butene is also used to produce the solvent butanone via hydration to 2-butanol 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[3]). The more elongated trans-molecule which has a tougher job to get its tail free from the liquid has the higher boiling point, the more rounded cis isomer escapes easier, thus having a lower boiling point. However, separation is unnecessary in most industrial settings, as both isomers behave similarly in most of the desired reactions. A typical industrial 2-butene mixture is 70% (Z)-2-butene (cis-isomer) and 30% (E)-2-butene (trans-isomer). Butane and 1-butene are common impurities, present at 1% or more in industrial mixtures, which also contain smaller amounts of isobutene, butadiene and butyne.[2]


  1. ^ cis-2-Butene, International Chemical Safety Card 0397, Geneva: International Programme on Chemical Safety, March 1996, http://www.inchem.org/documents/icsc/icsc/eics0397.htm . trans-2-Butene, International Chemical Safety Card 0398, Geneva: International Programme on Chemical Safety, March 1996, http://www.inchem.org/documents/icsc/icsc/eics0398.htm .
  2. ^ a b 2-Butene, SIDS Initial Assessment Report, Geneva: United Nations Environment Programme, February 1995, http://www.inchem.org/documents/sids/sids/107017.pdf .
  3. ^ Chemical Safety Information from Intergovernmental Organizations

External links