1,2-Butadiene is the organic compound with the formula CH<sub>2</sub>=C=CHCH<sub>3</sub>. It is an isomer of 1,3-butadiene, which is a common monomer used to make synthetic rubber, and is often co-produced with it. It is a colorless flammable gas, one of the simplest substituted allenes.
The C4-fraction of petroleum obtained by cracking and separated by distillation consists of many compounds, predominantly (75%) 1,3-butadiene, isobutene, and 1-butene. 1,2Butadiene comprises less than 1% or this mixture. It is partially purified by extraction with N-methylpyrrolidone. US production was 4,500âÂÂ23,000 tons in 2005.