Saponification

Saponification word originates from the Latin word ‘Sapo,’ meaning soap. It is the general process of the creation of soap. Soaps are the sodium salt or potassium salts of a long chain carboxylic acid or glycerol which has cleansing properties in water.

Saponification refers to the interaction of an ester with water and a base like NaOH or KOH, resulting in the formation of alcohol and the sodium or potassium salt of an acid.

In this article, we will understand the meaning, definition, equation, mechanism, and examples of Saponification. This article will cover the concept of Saponification value, its effects, and its applications. We will also provide solved examples and practice questions to understand this article.

What is Saponification?

Saponification is a straightforward method that is used in soap production. Soap contains potassium or sodium salts of a long-chain carboxylic acid or glycerol. This chemical transformation involves the interaction of ester with an inorganic base to give alcohol and soap. Saponification happens when triglycerides react with potassium or sodium hydroxide to generate glycerol and the salt of a fatty acid, commonly known as ‘soap.’ The conversion of oils and fats in the soaps through the action of aqueous is called the saponification process. KOH and NaOH are the alkalis used to produce alcohols and fatty acid salts.

Learn more about, Reaction of Ester

Definition of Saponification

Saponification is defined as the ester hydrolysis with NaOH or KOH, resulting in the production of alcohol and sodium or potassium salt of the acid. The conversion of fats, oils, and lipids into soap, facilitated by an aqueous alkali is known as saponification.

Both vegetable oil and animal fats, which are triesters or triglycerides, can undergo saponification in either a single or double-step process, interacts with aqueous hydroxide ions, leading to the formation of glycerol and derivatives of fatty acids.

Equation for Saponification

In the process of Saponification, esters split in the presence of aqueous alkali NaOH or KOH, resulting in the formation of an alcohol and fatty acid salts. Sodium hydroxide (NaOH), commonly known as lye is used for hard soap, while potassium hydroxide (KOH) is used for the production of soft soap.

The reaction involves the interaction of triglycerides with sodium hydroxide, a strong base to give glycerol (alcohol) and soap, specifically sodium palmitate. Similarly, the formation of potassium soap occurs when a strong potassium base such as KOH reacts with an ester.

Easter + Base → Alcohol + Soap.

The general reaction will be:

RCOOR’ + NaOH → ROH + R’COO– Na⁺

Mechanism of Saponification Reaction

The Saponification reaction mechanism consists of three steps:

Step 1: Nucleophilic Attack by Hydroxide Ion:

In the initial step, the ester group undergoes a nucleophilic attack by the hydroxide ion, resulting in the formation of an intermediate.

Step 2: Removal of Leaving Group (Alkoxide) and Orthoester Split:

In second step, the leaving group which is the alkoxide, is eliminated, causing the orthoester to undergo a split. This split gives a carboxylic acid (RCOOH) and an alkoxide group. The intermediate rearranges by releasing the leaving group in the process.

Step 3: Deprotonation:

The last step involves deprotonation, where the carboxylic acid and alkoxide undergo deprotonation. This deprotonation leads to the formation of alcohol and carboxylate ions. Specifically, the carboxylic acid undergoes deprotonation, resulting in the production of a carboxylate ion and alcohol as the hydrogen is removed.

Examples of Saponification

Sodium Stearate, Sodium Palmitate, Methyl Salicylate, Methyl Acetate and Methyl Benzoate are some of the common example of Saponification. Detailed description on few examples of Saponification is given below:

Sodium Stearate

Sodium stearate (C₁₈H₃₅NaO₂) is the sodium derivative of stearic acid (C₁₈H₃₆O₂). It serves as a key ingredient in soaps and detergents. It is produced through the hydrolysis of glyceryl tristearate ((C₁₈H₃₅O₂)₃C₃H₅) with aqueous sodium hydroxide (NaOH).

(C₁₈H₃₅O₂)₃C₃H₅ + 3NaOH → C₃H₅(OH)₃ + 3C₁₈H₃₅O₂Na

Sodium Palmitate

Sodium palmitate (C₁₆H₃₁NaO₂) is derived from the saponification of glyceryl palmitate ((C₁₆H₃₁O₂)₃C₃H₅) using sodium hydroxide (NaOH). It is present in soaps and detergents.

(C₁₆H₃₁O₂)₃C₃H₅ + 3NaOH → C₃H₅(OH)₃ + 3 C₁₆H₃₁O₂Na

Methyl Salicylate

Methyl salicylate (HOC₆H₄COOCH₃) reacts with sodium hydroxide (NaOH) to give a dense white solid known as sodium salicylate (HOC₆H₄COO–Na+) along with methanol (CH₃OH).

HOC₆H₄COOCH₃ + NaOH → HOC₆H₄COO–Na+ + CH₃OH

1-Step Saponification vs 2-Step Saponification

The Saponification process can occur through either a one-step or a two-step method for transforming triglycerides into soaps. In the one-step approach, triglycerides undergo hydrolysis with a strong base, leading to the split of the ester bond and the liberation of glycerol along with fatty acid salts (soaps).

On the other hand, the two-step saponification process involves the initial steam hydrolysis of triglycerides, resulting in the formation of glycerol and carboxylic acid in its original form, rather than as a salt. In the subsequent step, an alkali is used to neutralize these carboxylic acids to produce the soap.

Saponification Value

The Saponification Value is also referred to as the saponification number, signifies the quantity of base (either KOH or NaOH) required to saponify 1 mg of fat under specific conditions. It is expressed in terms of KOH. It is the milligrams of KOH needed to saponify one gram of fat under controlled circumstances.

This value is essentially an indicator of the average molecular weight of all fatty acids present in the given sample in the form of triglycerides. The formula for calculating the saponification value is represented as follows:

SV = {(B−S)×M×56.1}/W

Where,

• (B-S) denotes the difference in the volume of HCl solution used for the blank run and the tested sample in millilitres.
• M represents the molarity of the HCl solution.
• 56.1 is the molecular weight of KOH.
• W is the weight of sample in grams.

Importance of Saponification Value

• Fatty acids characterized by longer carbon chains typically exhibit lower saponification values.
• The saponification value of fatty acids with a long carbon chain is generally low.
• Fatty acids with shorter carbon chain tend to a higher saponification value. For example, the saponification value of butter is 230–240, because it composed of longer-chain fatty acids whereas human fat composed shorter-chain fatty acids, contains a value of 195–200.
• It estimates the rough average molecular weight of the fat or oil used in saponification process. The saponification value increases with decreasing molecular weight.
• Saponification value not only aids in determining the amount of base for saponification but also facilitates the calculation of chain lengths within the fatty acids.

Significance of Saponification

Saponification finds diverse and significant applications across various industries:

• In commercial sectors, saponification quantifies the levels of free fatty acids.
• Saponification is used in the formulation of fire extinguishers.
• Primary application of saponification is in the manufacturing of detergents and a variety of soaps. Different alkali is used in this process such as potassium hydroxide for soft soaps or sodium hydroxide for hard soaps.
• Saponification is used in art restoration in the terms of implications of oil paintings.
• Sodium-based soaps derived from saponification are key components in laundry detergents. It serves as effective agents in household cleaning. For example Lithium soaps are used in domestic as well as industrial cleaning.
• Saponification is integral in the food sector. It aids in the determination of free fatty acid content in food products.

Saponification’s Effects on Soap

The Saponification process induces significant changes in the soap molecule:

• Saponification converts carboxylic acid group (COOH) into a carboxylate ion (COO^–) to form a salt.
• This means that the soap molecule undergoes increased water solubility, facilitating easy rinsing and removal.
• Sodium or Potassium ions (Na⁺or K⁺) initially attached to the soap molecule are eliminated during saponification. This results in the soap molecule acquiring an electric charge.
• In addition, the sodium or potassium ions (Na⁺or K⁺) attached to the soap molecules are also removed, so the soap molecule is now charged.
• Here, soap bubbles show an inherent attraction to each other and to objects possessing opposite charges. This charged nature enhances the effectiveness of soap.

Effects of Saponification

The Saponification process gives both favorable and unfavorable outcomes:

Positive Effects – Fire Extinguishers

Primarily, Saponification serves a beneficial role in fire extinguishers by transforming fats and oils into non-combustible soaps. This not only aids in extinguishing fires but also contributes to a reduction in flame temperature as it absorbs heat from the surroundings.

Negative Effects – Art Damage

However, Saponification can harms to oil paintings, as the metals present in pigments can react with the oil. The fatty acids in the oil make it susceptible to damage over time. It can compromise the integrity of artworks.

Everyday Use – Soaps

Soaps are integral to our daily lives and play diverse roles. Sodium soaps are used for cleaning clothes, potassium soaps find use in general cleaning applications, and lithium soaps serve as effective lubricants for greases. These variations reflect the versatility of soaps in our daily routines.

Saponification Vs Esterification

The formation of an ester takes place usually by combining acid and alcohol while releasing water, although, saponification induces the breakdown of ester bonds, which leads to the creation of fatty acid derivatives with long chains.

Example of Esterification:

C₂H₅OH + CH₃COOH → CH₃COOC₂H₅ + H₂O

Difference between Esterification and Saponification is given below:

Difference between Esterification and Saponification
Esterification	Saponification
It is the process that used in the formation of esters.	It is the process that used in making soap.
It reacts in the presence of strong sulfuric acid, carboxylic acid and alcohol.	In this process, ester and aqueous alkali react.
Heat is evolved	No heat is evolved.
Acid catalyst is used.	Base catalyst is used.
Water is the byproduct in this process.	Alcohol is the byproduct in this process.

Read More,

• Alcohols, Phenols and Ethers
• Physical properties of Alcohols, Phenols and Ethers
• Chemical reactions of Alcohols, Phenols and Ethers

Examples on Saponification

Example 1: 5 grams of an oil sample underwent reaction with 50 mL of a 0.5 N alcoholic potassium hydroxide (KOH) solution. After refluxing for 2 hours , the mixture was titrated by 15 ml of 0.5 N HCl. Determine the Saponification value.

Solution:

Saponification value = (Blank titration reading – Back titration reading) X Normality of KOH X 56 /weight of oil

= (50 -15) x 0.5 x 56 / 5

= 196 mg of KOH /gm of oil.

Example 2: If the palm oil weight is 8 grams. Then find the Saponification Value that it takes 30 mL of a 0.1 M sodium hydroxide (NaOH) solution to neutralize the liberated fatty acids.

Solution:

B−S=Volume of NaOH used for blank−Volume of NaOH used for sample

B−S=Vblank−Vsample

B−S=30mL−0mL

Amount of NaOH used (nNaOH): nNaOH=Molarity × Volume

nNaOH=0.1mol/L×(30×10⁻³L)

nNaOH=0.003mol

Saponification value (SV): SV={(B−S)×M×56.1}/W

SV=(30×10⁻³)×0.1×56.1/8 g

SV=0.21075mg KOH/g.

Practice Questions on Saponification Value

Q1. Choose the option that accurately characterizes saponification.

• A. Formation of alcohol and carboxylic acid by breaking ether molecules.
• B. Synthesis of an ether through the combination of two alkyl groups.
• C. Cleavage of ester molecules resulting in the production of alcohol and carboxylic acid.
• D. Hydrolysis of salt accompanied by the introduction of a weak acid.

Q2. Identify the oil or fat that is resistant to Saponification among the given options.

• A. Shea butter
• B. Bee wax
• C. Olive oil
• D. Paraffin wax

Q3. Highlight the compound that is industrially manufactured via the process of Saponification from the options provided.

• A. Sodium chloride
• B. Sodium hydroxide
• C. Glycerol
• D. Potassium hydroxide

Q4. Identify the chemical compound utilized to induce the precipitation of soap during the salting-out process.

• A. Sodium chloride
• B. Sodium hydroxide
• C. Glycerol
• D. Potassium hydroxide

Saponification-FAQs

1. What is Meaning of Saponification?

Saponification is the straightforward method which is used in soap production. Soap contains potassium or sodium salts of a long chain carboxylic acid or glycerol. This chemical transformation involves interaction of ester with an inorganic base to give alcohol and soap.

2. What is Chemical Equation of Saponification?

Easter + Base → Alcohol + Soap

The general reaction will be: RCOOR’ + NaOH → ROH + R’COO– Na⁺

3. What are Examples of Saponification?

Sodium Stearate, Sodium Palmitate, Methyl Salicylate, Methyl Acetate and Methyl Benzoate are the example of Saponification.

4. What is the Use of NaOH in Saponification?

KOH and NaOH are the alkalis used to produce alcohols and fatty acid salts. Sodium hydroxide (NaOH), commonly known as lye is used for hard soap.

5. What type of Reaction Saponification is?

Saponification process is the hydration reaction.

6. What is Saponification Value?

The saponification value is also referred to as the saponification number, signifies the quantity of base (either KOH or NaOH) required to saponify 1 mg of fat under specific conditions. It is expressed in terms of KOH.

7. What is the Mechanism of Saponification?

• Step 1: Nucleophilic Attack by Hydroxide Ion:
• Step 2: Removal of Leaving Group (Alkoxide) and Orthoester Split:
• Step 3: Deprotonation

8. Is the Saponification process Exothermic or Endothermic?

Saponification process is an exothermic reaction.

9. What Factors Affect Saponification.

Ethanolic KOH content, reaction temperature, and reaction time affects Saponification.

10. What is the Chemical name for Soap?

Soaps are derived from Sodium or Potassium salts of long-chain carboxylic acids. The chemical formula for Soap is represented as C₁₇H₃₅COONa or Sodium Stearate, which is a common example of a Soap compound.