Dehydration to alkenes
Converting an alcohol to an alkene requires removal of the hydroxyl group and a hydrogen atom on the neighbouring carbon atom. Because the elements of water are removed, this reaction is called a dehydration. Dehydrations are most commonly carried out by warming the alcohol in the presence of a strong dehydrating acid, such as concentrated sulfuric acid.
Most alcohol dehydrations take place by the mechanism shown below. Protonation of the hydroxyl group allows it to leave as a water molecule. The species that remains has a carbon atom with only three bonds and a positive charge and is called a carbocation. This intermediate species can be stabilized by loss of a proton from a carbon atom adjacent to the positively charged carbon ion, giving the alkene.