There are many equilibrium reactions that yield water as a co-product where removal of the water as it is produced is necessary to drive the reaction to completion and this is done using a Dean - Stark apparatus. The reaction is carried out under reflux in a solvent which is less denseb than water, both immiscible with it and forms an azeotrope. The apparatus allows the water to be separated from the condensed azeotrope preventing it from returning to the reaction mixture.