A base is a proton (H+) acceptor. In organic chemistry the hydroxide ion and amines are the most common bases.The hydroxide ion accepts a proton to form water. Sodium hydroxide neutralises carboxylic acids to give a salt and water, and reacts with phenol to form sodium phenoxide.Amines act as bases because the nitrogen atom has a lone pair that can accept a proton. Methylamine reacts with acids to form a methylammonium salt.Hydroxide ions in ethanol can also act as a base towards halogenoalkanes, removing a proton and causing elimination to give an alkene.