2-Butene

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 geometric isomers cis-2-butene ((Z)-but-2-ene) and trans-2-butene ((E)-but-2-ene).

2-Butene

cis trans
cis trans
Names
Preferred IUPAC name But-2-ene
Other names β-Butylene
Identifiers
CAS Number	107-01-7 Y (cis): 590-18-1 Y (trans): 624-64-6 Y
3D model (JSmol)	Interactive image (cis): Interactive image (trans): Interactive image
Beilstein Reference	1718755 1361341
ChEBI	CHEBI:48363 Y (cis): CHEBI:48366 (trans): CHEBI:48365
ChemSpider	11719 Y (cis): 4449912 N (trans): 56442 N
ECHA InfoCard	100.003.140
EC Number	203-452-9
Gmelin Reference	25196 1140 1141
PubChem CID	(cis): 5287573 (trans): 62695
RTECS number	EM2932000 1718756
UNII	S1SK37516R Y (cis): L35ORC9C05 Y (trans): 017NGL487F Y
CompTox Dashboard (EPA)	DTXSID1026748
InChI InChI=1S/C4H8/c1-3-4-2/h3-4H,1-2H3 Y Key: IAQRGUVFOMOMEM-UHFFFAOYSA-N Y InChI=1/C4H8/c1-3-4-2/h3-4H,1-2H3 Key: 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)[1] 0.626 g/ml (trans, 0.9 °C)[2]
Melting point	−138.9 °C (−218.0 °F; 134.2 K) (cis)[1] −105.5 °C (trans)[2]
Boiling point	0.8 to 3.7 °C (33.4 to 38.7 °F; 273.9 to 276.8 K) (Z = 3.7 °C)[1] (E = 0.8 °C)[2]
Magnetic susceptibility (χ)	−42.6·10−6 cm3/mol (cis) −43.3·10−6 cm3/mol (trans)
Hazards[3]
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H220
Precautionary statements	P210, P377, P381, P403
NFPA 704 (fire diamond)	1 4 0
Flash point	−72 °C (−98 °F; 201 K)[1][2]
Autoignition temperature	325 °C (617 °F; 598 K)[1][2]
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 [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

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,^[4] although some 2-butene is also used to produce the solvent butanone via hydration reaction 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^[5]). 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)-but-2-ene (cis-isomer) and 30% (E)-but-2-ene (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.^[4]