But-2-ene

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).

But-2-ene

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 gasoline (petrol) and butadiene,^[4] 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^[5]). 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.^[4]

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

• SIDS Initial Assessment Report for 2-Butene from the Organisation for Economic Co-operation and Development (OECD)