Butene, also known as
butylene, is an
alkene with the formula
C4H8. It is a colourless gas that is present in
crude oil as a minor constituent in quantities that are too small for viable extraction. It is therefore obtained by
catalytic cracking of long chain hydrocarbons left during refining of crude oil. Cracking produces a mixture of products, and the butene is extracted from this by
fractional distillation.