1,2-Butadiene
{{Chembox
|ImageFile = Buta-1,2-dien.svg
|ImageFile2=1,2-Butadiene-3D-balls.png
| PIN = Buta-1,2-diene
| OtherNames = Methyl allene
|Section1 = {{Chembox Identifiers
|CASNo = 590-19-2
|PubChem = 11535
| EC_number = 209-674-2
| UNII = 2AZI943A8R
| ChEBI = 39480
| Gmelin = 1144
| Beilstein = 1730808
| ChemSpiderID = 11051
| StdInChI=1S/C4H6/c1-3-4-2/h4H,1H2,2H3
| StdInChIKey = QNRMTGGDHLBXQZ-UHFFFAOYSA-N
| SMILES = CC=C=C
}}
|Section2 = {{Chembox Properties
|C=4|H=6
|BoilingPtC = 10.9
|MeltingPtC = −136.2
|Density = 0.676 at 4 °C
|RefractIndex = 1.4205 at 1 °C
}}
|Section4 = {{Chembox Thermochemistry
|DeltaHvap = 23.426 kJ/mol
}}
|Section7 = {{Chembox Hazards
| MainHazards = Frostbite, flammable
| FlashPtC = −75
| GHSPictograms = {{GHS02}}{{GHS09}}
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|220|224|411}}
| PPhrases = {{P-phrases|210|233|240|241|242|243|273|280|303+361+353|370+378|377|381|391|403|403+235|410+403|501}}
}}
}}
1,2-Butadiene is the organic compound with the formula CH2=C=CHCH3. It is an isomer of 1,3-butadiene, a common monomer used to make synthetic rubber. It is a colorless flammable gas, one of the simplest substituted allenes.{{cite web|url=https://www.exxonmobilchemical.com/dfsmedia/f743208d804841f6ab89a60202cc3f56/2031-source?extension=pdf/options/download|date=March 2016|publisher=ExxonMobil|title=Product Safety Summary 1,2-BUTADIENE|archive-url=https://web.archive.org/web/20231124172306/https://www.exxonmobilchemical.com/dfsmedia/f743208d804841f6ab89a60202cc3f56/2031-source?extension=pdf/options/download |archive-date=2023-11-24 |url-status=dead}}
Production
The C4-fraction obtained by cracking and separated by distillation consists of many compounds, predominantly (75%) 1,3-butadiene, isobutene, 1-butene. 1,2-Butadiene comprises less than 1% or this mixture.{{Ullmann|title=Butadiene|author1=J. Grub |author2= E. Löser|year=2012|doi=10.1002/14356007.a04_431.pub2}} It is partially purified by extraction with N-methylpyrrolidone. US product was 4,500 - 23,000 tons in 2005.