What is Hydrolysis

Hydrolysis, also known as hydrolysis reaction, is a type of decomposition reaction in which a molecule is broken down into components by adding water. The entire molecule changes its structure as new bonds are formed. It is the reverse of dehydration synthesis or condensation reaction, where molecules combine to form larger molecules. If the hydrolysis reaction occurs in little water, partial hydrolysis is known ^[1-7].

The word hydrolysis comes from two words – ‘hydro’ means water, and ‘lysis’ means ‘break down.’

What Happens During a Hydrolysis Reaction

In a hydrolysis reaction, the molecule breaks down into two components. One fragment of the original molecule gains a hydrogen ion (H⁺), and the other fragment gains a hydroxyl ion (OH^–). A typical feature of organic compound hydrolysis is that a third substance, usually an acid or a base, increases the rate of chemical change.

General Equation for Hydrolysis

How to Write a Hydrolysis Equation

The general formula for hydrolysis reaction is:

AB + H₂O → AH + BOH

Types of Hydrolysis

The different types of hydrolysis are as follows ^[1-6]:

1. Salts

Salts are divided into three categories – acid salt, basic salt, and neutral salt. Hydrolysis of salts occurs when salts of a weak acid and base dissolve in water. In this process, they break down into ions – cations and anions.

Example: Dissolving sodium acetate (CH₃COONa) in water gives sodium (Na⁺) and acetate (CH₃COO^–) ions. The acetate combines with a proton to give acetic acid (CH₃COOH).

CH₃COO^–Na⁺ + H₂O → CH₃COOH + Na⁺ + OH^–

Similarly, ammonium chloride (NH₄Cl) dissolves in water to give ammonium (NH₄⁺)and chloride ions (Cl^–), and sodium carbonate (NaCO₃) gives carbonic acid (H₂CO₃) and sodium hydroxide (NaOH).

2. Sugar

Sugar consists of carbohydrates. The hydrolysis of sugar is known as saccharification, which commonly occurs in the body. This process breaks down complex sugar (disaccharides), like sucrose and lactose, into simple components (monosaccharides).

Example: Hydrolysis of sucrose breaks down into glucose and sucrose. However, the process is prolonged unless an enzyme is added.

C₁₂H₂₂O₁₁ + H₂O → C₆H₁₂O₆ + C₆H₁₂O₆

Similarly, the hydrolysis of lactose produces β-D-glucose and β-D-galactose.

3. Acid-Base

The acid-base catalysis is found during the hydrolysis of amides and esters.

3a. Ester: During ester hydrolysis, an ester bond breaks down with a water molecule to form a carboxylic acid and an alcohol. The general formula for esterification is:

RCO-OR’ + H₂O → RCO-OH + R’-OH

Example: Butyl acetate reacts with water to form acetic acid and butanol.

CH₃COOCH₂CH₂CH₂CH₃ + H₂O → CH₃CO-OH + CH₃CH₂CH₂CH₂-OH

3b. Amide: During hydrolysis of an amide, the carbon-nitrogen bond breaks down and produces a carboxylic acid and ammonia or amine. This process is not easy to carry out, and the reaction is much slower. The general formula is given by:

RCO-NR^’ + H₂O → RCO-OH + R^’-NH

The rate of hydrolysis reactions is typically expressed in terms of the acid-catalyzed and base-catalyzed hydrolysis rate constants.

4. Adenosine triphosphate (ATP)

The ATP hydrolysis takes place in biology, and the reaction is catalyzed by enzymes, which is given as follows:

ATP + H₂O → ADP + inorganic phosphate + energy

The energy released from this hydrolysis reaction is used to perform cellular work, usually by coupling the exergonic reaction of ATP hydrolysis with endergonic reactions.

Applications of Hydrolysis

The hydrolysis reaction has applications in both chemistry and biology.

The catalyzed hydrolysis reaction is applied during the digestion of proteins, carbohydrates, and lipids by enzymes in the digestive tract. This process helps the small intestine to absorb nutrients more efficiently. For example, the enzyme amylase is responsible for breaking down starch into smaller sugars ^[1].

Ester hydrolysis is applied to create soaps, which are the salts of fatty acids from triglycerides. The alkaline hydrolysis of the ester is called saponification.

Condensation vs. Hydrolysis

Condensation is the opposite of hydrolysis. While hydrolysis is the breaking of bonds using water, condensation forms a new bond to form a large molecule along with a small molecule, typically water. The following table lists the difference between condensation reaction and hydrolysis.

	Condensation	Hydrolysis
Definition	Synthesis of a larger molecule from two smaller molecule	Breakdown of a larger molecule into smaller fragments
Water	Water can form as a byproduct	Water is consumed in the reaction
Example	Synthesis of a dipeptide from amino acids	Hydrolysis of sucrose gives glucose and sucrose

Hydrolysis vs. Hydration

The difference between hydration and hydrolysis is that hydrolysis is breaking compounds using water. In contrast, hydration is an electrophilic addition reaction where there is no cleavage of the original molecule. Instead, a water molecule is added to the substance.

Example: Copper sulfate hydrates to give hydrated copper sulfate.

CuSO₄ + 5H₂O → CuSO₄.5H₂O

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