Ester - Introduction, Nomenclature, Preparation, Physical and Chemical Properties, Uses, Practice Problems & FAQs

Many of you must have seen advertisements on television. Soaps and detergents advertisements are more frequent in nature. Your favourite actors perform those advertisements so that the company gets more profit. These are marketing strategies.

Well! I am not interested in telling you about your favourite actors and their advertisements, I am interested in telling you about the ingredients which are used by the industrialists. Major components used in soaps and detergents are esters. Using sodium hydroxide solution, alkaline hydrolysis is used to break down large esters present in animal and plant fats and oils and then used for making soap and detergents.

There are a lot of major applications of esters, we will study those in this concept page.

Let’s begin to study this versatile compound and find out how it works chemically and what its uses are!

TABLE OF CONTENT

• What is an ester?
• Nomenclature
• Preparation of ester
• Physical Properties of ester
• Chemical Properties of ester
• Uses of Ester
• Practice Problems
• Frequently asked questions-FAQs

What is an ester?

When a hydroxyl group is replaced by an alkoxy group in a chemical compound generated from an acid (organic or inorganic), the result is known as an ester. To put it simply, esters are a class of chemical compounds created by the bonding of an alcohol group with a collection of organic acids while leaving water molecules.

Nomenclature of Esters:

An ester is obtained when a carboxylic acid reacts with alcohol along with the removal of water.

Generally, esters are named alkyl alkanoate. The alkyl group that is bonded to O (as OR) is termed alkyl, whereas the rest of the molecule is termed alkanoate.

The secondary suffix - oate

The special suffix - carboxylate

Examples:

Serial  number	IUPAC nomenclature	Secondary Prefix	Primary Prefix	Word Root	Primary Suffix	Secondary Suffix
1		ethyl	-	meth	ane	-oate
2		methyl	-	eth	ane	-oate
3		ethyl	-	eth	ane	-oate
4		methyl	cyclo	hex	ane	carboxylate

Preparation of Ester:

The general term for a chemical reaction in which two reactants (usually alcohol and an acid) combine to create an ester as the end product is "esterification." Esters are frequently found in organic chemistry and biological materials, and they frequently have a distinctive, fruity scent. As a result, the fragrance and flavor business uses them extensively. Numerous polymers also contain ester linkages.

1. Esterification of carboxylic acids with alcohols:

Fischer esterification is a traditional synthesis that includes reacting an alcohol with a carboxylic acid in the presence of a dehydrating agent.

RCOOH+R'-OH ⇌ RCOOR'+H2O

2. Alcoholysis of acyl chlorides and acid anhydrides:

Esters are produced when alcohols combine with acyl chlorides and acid anhydrides.

Reaction with Acyl chloride:  ROCl+R'OH RCO2R'+HCl

Reaction with Acid anhydride:  (RCO)2O+R'OH RCO2R'+RCO2H

Physical Properties of ester:

• Esters of lower acids are colorless, pleasant-smelling solids, while those of higher acids are solids.
• Esters are less polar than alcohols and more polar than ethers.
• Methyl and ethyl esters have lower boiling points than their respective parent acids.
• Lower esters are largely water soluble. Esters are rapidly less soluble in water as their mass increases.
• Unlike their parent alcohols, they can participate in hydrogen bonds as hydrogen-bond acceptors but not as donors. This capacity for hydrogen bonding confers some degree of water solubility. 
• Esters cannot self-assemble due to their inability to donate hydrogen bonds. Therefore, compared to carboxylic acids of the same molecular weight, esters are more volatile.

Chemical properties of ester:

1. Preparation of Aldehyde:

Aldehyde can be prepared by reducing esters using suitable reducing agents.

Below is the general reaction mentioned:

2. Preparation of Carboxylic Acids:

Basic hydrolysis produces carboxylates, which, when acidified, yield the appropriate carboxylic acids, acidic hydrolysis of esters results in the production of carboxylic acids immediately.

3. Hydrolysis and saponification:

Esterification is a reaction that can be stopped. Esters are hydrolyzed in both acidic and basic environments. The process is the reverse of Fischer esterification under acidic circumstances.

Under basic circumstances, an alkoxide serves as the leaving group while hydroxide works as a nucleophile. The process of manufacturing soap is based on a reaction called saponification.

Uses of Ester:

Here are some esters' uses:

• Esters with pleasant aromas are utilized in fragrances, essential oils, food flavorings, cosmetics, and other products.
• As an organic solvent, it is employed in many reactions.
• Pheromones contain organic esters.
• Fatty acid esters of glycerol are what make up naturally occurring fats and oils.
• Nitroglycerin and other nitrate esters are employed as explosives.
• Polyesters can be further processed to create textile fibers for use in garments.
• Making detergents and surfactants, such as soap, uses it.

Practice Problems:

Q1. Which of the following is employed as a catalyst to convert carboxylic acid and alcohol into esters in the acidic medium?

A. Sulphuric acid

B. Nitrous acid

C. Sulfurous acid

D. Nitric acid

Answer: A

Solution: The Fischer esterification is a traditional synthesis that includes reacting an alcohol with a carboxylic acid in the presence of a dehydrating agent. For common esters, like ethyl acetate, the equilibrium constant for such reactions is around 5. In the absence of a catalyst, the reaction proceeds slowly. The typical catalyst for this reaction is sulfuric acid.

Q2. Which of the following compounds is produced when an ester is hydrolyzed in a basic medium?

A. Alcohol and sodium carboxylate

B. Ether and alcohol

C. Sodium carboxylate

D.Aldehyde and alcohol

Answer: A

Solution: An alkoxide is a leaving group in basic circumstances, while hydroxide acts as a nucleophile.

Q3. What fragrance does ester typically have?

A. Fish-like smell

B. Alcoholic smell

C. Fruity-like smell

D. Rotten egg smell

Answer: C

Solution: Many esters naturally arise in plant essential oils and have distinct fruity scents. As a result, they are frequently used in synthetic flavourings and fragrances that are meant to replicate natural scents.

Q4. Which of the mentioned chemicals is an ester?

A.

B.

C.

D.

Answer: A

Solution: The modified carboxyl group, in which the H of the -OH group is replaced by an alkyl group to form the generic functional group -COOR, is what distinguishes esters from other chemical compounds.

Frequently asked questions-FAQs:

1. What circumstances must exist for an ester to form?

Answer: When alcohols and carboxylic acids are heated together in the presence of an acid catalyst, esters are created. Usually, concentrated sulfuric acid serves as the catalyst. In some circumstances, dry hydrogen chloride gas is employed, but these typically involve aromatic esters (ones where the carboxylic acid contains a benzene ring).

2. Out of acidic and basic hydrolysis of ester, which will be faster?

Answer:  Acidic hydrolysis will be faster because -OH leaves as a good leaving group i.e. H2Ounlike in basic hydrolysis where it leaves as OH- which is a poor leaving group.

3. Are esters flammable in nature?

Answer: Many esters are highly flammable or flammable at all. Low flash points and broad flammability limitations of low-molecular-weight esters, such as methyl formate, make them hazardous flammability hazards.

4. Why do soaps contain esters?

Answer:  By reacting with water and a base, esters can be split back into carboxylic acid and alcohol. From the Latin sapo, which signifies soap, the reaction is known as saponification. The name is derived from the fact that fats were once hydrolyzed into esters to produce soap.

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