If a haloalkane is heated with concentrated alcoholic potassium hydroxide, the major product formed is an alkene due to the elimination of hydrogen halide. This is called β-elimination or dehydrohalogenation.

Saytzeff's Rule

If the structure of alkyl halide is such that it can undergo elimination in two different ways, then the more highly substituted alkene (having lesser number of hydrogen atoms on the doubly bonded carbon atoms) is the major product of elimination. For example, elimination reaction of 2-bromobutane gives 2-butene as major product according to the Saytzeff's rule.