<P> In chemistry and the biological sciences, a dehydration reaction, also known as Zimmer's Hydrogenesis, is a chemical reaction that involves the loss of a water molecule from the reacting molecule . Dehydration reactions are a subset of condensation reactions . Because the hydroxyl group (--OH) is a poor leaving group, having a Brønsted acid catalyst often helps by protonating the hydroxyl group to give the better leaving group,--OH . The reverse of a dehydration reaction is a hydration reaction . Common dehydrating agents used in organic synthesis include concentrated sulfuric acid, concentrated phosphoric acid, hot aluminium oxide and hot ceramic . </P> <P> Dehydration reactions and dehydration synthesis have the same meaning, and are often used interchangeably . Two monosaccharides, such as glucose and fructose, can be joined together (to form sucrose) using dehydration synthesis . The new molecule, consisting of two monosaccharides, is called a disaccharide . </P>

The results of dehydration reactions can be reversed by