Difference Between Hydrolysis and Dehydration Synthesis

Hydrolysis vs Dehydration Synthesis

Hydrolysis and dehydration synthesis are two main reactions used in organic synthesis procedures. Apart from their industrial and experimental uses these two reactions are especially important in biological systems. They play quite a big role in our metabolic activities and are always mediated by enzymes, to perform selective hydrolysis or dehydration synthesis.


Hydrolysis is a term which comes from Greek origin. Hydro means water and lysis means separation; which gives us the meaning “separating with the use of water”. If a molecule gains a water molecule and breaks down into parts, this process is called hydrolysis. Breaking of bonds as we all know is a degrading process, and this reaction, therefore, comes under catabolism when applied to biological systems. Not all bonds can be hydrolyzed. Some frequent examples are hydrolysis of salts of weak acids and weak bases, hydrolysis of esters and amides, and hydrolysis of biomolecules like polysaccharides and proteins. When a salt of a weak acid or base is added to water, water spontaneously breaks in to H+ and OH- and forms the conjugate base or acid making the medium acidic or basic depending on the substance. Ester and amide bonds are hydrolyzed in synthetic organic reactions as well as in biological systems.

Hydrolysis is bond breakings process hence a way to release energy. It is the main reaction involved in energy release inside our bodies. The complex molecules we eat as food are broken down to simple molecules by various enzymes and the released energy is stored in ATP; the energy currency of the body. When energy is needed for biosynthesis or active transport of substances through cell membranes, ATP is hydrolyzed, and the stored energy is released.

Dehydration Synthesis

Dehydration synthesis, as the name implies, is a process which synthesizes molecules by removing water molecules. There are two main ways to do this. One is to remove a water molecule from one substance yielding an unsaturated bond. This is done by protonating OH- on to OH2+ and thereby making it a good leaving group. Dehydrating agents such as Conc. Sulfuric, Conc. Phosphoric and Aluminium oxide are very popular for this reaction. The other method is to bring two separate molecules and, by removing a OH- from one and a H+ from the other, condensing them into one large molecule. This is used in organic reactions like aldol condensation, ester synthesis and amide synthesis. The type two is used in biological systems to biosynthesis molecules.

Polysaccharide synthesis by using mono and disaccharides, protein synthesis by using amino acids are two main examples. Since the reaction here is involved in bond making, it is an anabolic reaction. Unlike hydrolysis, these condensation reactions require energy. In synthetic organic chemistry, it is provided as thermal energy, pressure etc. and in biological systems by ATP hydrolysis.

What is the difference between Hydrolysis and Dehydration Synthesis?

• Hydrolysis is a process where a water molecule is added to a system, but dehydration synthesis is a process where a water molecule is removed from a system.

• Hydrolysis separates molecules into parts (mostly) and dehydration synthesis condenses molecules into a larger molecule.