Condensation Reaction:Types of Condensation Reactions, Practice problems and Frequently asked questions(FAQs)

Condensation is a phenomenon that we encounter on a daily basis.

On a hot day with high temperatures, you will notice that the mirror has fogged up after taking a hot water shower.

There are little beads of water on the mirror when you touch it.

How did this fog form? Where did these water beads come from?

This phenomenon is known as condensation.

It is the process of converting water vapour in the air into liquid water. Water vapour is the gaseous form of water that is present in the air.

Condensation is vital to the survival of life on Earth. When water molecules are heated, they begin to attract one another. They start to move rapidly and lose mass, causing them to rise. When a gas cools, the water molecules attract one another and fall as rain. Rain is the world's primary source of freshwater. Condensation is also beneficial in agriculture. When condensed water falls to the earth as precipitation, it makes water available to plants and animals. The process of condensation is crucial to human life. If condensation did not occur, water vapor would remain gaseous, and gaseous water would be incapable of supporting human life.

Table of content:

• Condensation reactions
• Types of condensation reactions
• Practice problems
• Frequently asked questions(FAQs)

Condensation reactions:

In organic chemistry, a condensation reaction is a specific type of chemical reaction in which two molecules combine to form one molecule, typically with the loss of a minor molecule like water. If water is lost during the reaction, it is also referred to as a dehydration synthesis. Other substances can also be lost, including ammonia, ethanol, acetic acid, and hydrogen sulfide.

Amino acids are biological compounds that have an amine functional group on one end of the molecule and a carboxylic acid functional group on the other. Two amino acids can combine in a condensation reaction, and a covalent bond is formed between the amine nitrogen of the first amino acid and the carboxyl carbon of the second amino acid. This produces a water molecule, which is eliminated during the condensation process.

Types of condensation reactions:

1. Aldol condensation:

In the presence of a diluted base, aldol condensation takes place in -hydrogen-containing aldehydes and ketones, resulting in the formation of -hydroxy aldehydes or -hydroxy ketones, which are known as aldols. When aldol is subjected to condensation (or elimination) in the presence of heat, this reaction is most frequently referred to as aldol condensation.When a condensation reaction occurs between two different carbonylcompounds, it is calledcross-aldol condensation. A noteworthy feature of the Aldol reaction is that the carbon-carbon bond formation takes place between the alpha-carbon atom of one aldehyde and the carbonyl group of the other. This is because the generation of the enolate of one carbonyl can involve the proton abstraction from the alpha-carbon atom of the other carbonyl.

The process of aldol condensation involves a nucleophilic attack of enolate on a carbonyl to produce a β-hydroxy ketone or β-hydroxy aldehyde. The catalyzation of the aldol condensation reaction can be carried out with the help of an acidic or basic solution in the presence of heat.

Bases such as hydroxide ions and alkoxide ions are used for the partial conversion of an aldehyde to its enolate anion.

The enolate undergoes a nucleophilic addition to the carbonyl group. This is achieved in a solution that contains both an aldehyde and its enolate. Aldol condensation is prominent in those aldehydes that have an α-hydrogen along with a dilute base to give β-hydroxy aldehydes, also called aldols. When the above reaction takes place between two different carbonyl compounds, it is referred to as the Crossed Aldol Condensation Reaction. When both the aldehydes possess α-hydrogens, then they can both form carbanions (enolate) and that can also act as acceptors of enolates. Thus, the reaction results in a mixture of four products that have a minute synthetic value. In case any of the aldehydes does not have α-hydrogen, then it can only act as an acceptor of Carbanion. Thus, only two products will be formed on the completion of the reaction. Also, the condensation of the initial products takes place rapidly and thus leads to the formation of -unsaturated ketone or aldehyde.

Mechanism of Aldol condensation:

STEP 1: Aldehyde is subjected to deprotonation done by the hydroxide ion that functions as a base and thus abstracts the alpha-hydrogen which results in the formation of the enolate/carbanion.

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STEP 2: Enolate ion/carbanion attaches itself to the aldehyde at the site of the electrophilic carbonyl carbon, and results in the formation of an alkoxide intermediate.

STEP 3: Alkoxide ion now deprotonates the water molecule resulting in the formation of hydroxide ion and the β–hydroxy aldehyde.

STEP 4:Aldol formed in the above step is converted into enolate ion by hydroxide ion through the mechanism. And enolate ion formed in this step loses hydroxide ion to form

-unsaturated aldehyde.

Applications of Aldol condensation

• This reaction is used to form a carbon-carbon bond in the process of gluconeogenesis and photosynthesis.
• It finds numerous importance and applications in the discipline of metabolism biochemistry and thus finds direct applications in the method of glycolysis; where it works to end the carbon-carbon end; which is contradictory to its role in the process of gluconeogenesis.
• It is used in the production of alcohol, isophorone and diacetone.
• It also finds applications as an intermediate in the process of perfume production.
• It is used in pharmaceutical manufacturing.
• It is used in the synthesis of pesticides as well.
• It is used in the synthesis of unsaturated ketones and chalcones (also known as aromatic ketones).

2. Cross aldol condensation

A cross-aldol condensation reaction is the condensation of two distinct molecules of an aldehyde or ketone in a protic solvent like water, alcohol, or a basic media. If both aldehydes have alphahydrogen, then they both form carbanions(enolate) and also canfunction as carbanionreceptors. Therefore, 4 products will be formed in the reaction.One of the aldehydes only functions as a carbanion acceptor if it lacks alpha hydrogen. Only two items are produced in these circumstances.

Example of cross aldol condensation reaction

A common substrate forcross-aldol reactions isaromatic aldehydes that do not have an alpha-H. Aromatic aldehyde reacts with any aldehyde/ketone having alpha-H leading to the formation of α,β-unsaturated carbonyls.

The reaction between benzaldehyde and acetophenonecauses cross-aldol condensation inthe presence ofdiI. . In thisreaction, benzaldehydedoes not have an alphahydrogen, but acetophenonehas alphahydrogen, soit undergoes aldol condensationto formβ-hydroxyketone. In addition, dehydration leads to the formation of α,β-unsaturated ketones.

3. Claisen condensation

To produce β-keto ester, two molecules of ester containing alpha-hydrogen undergo self-condensation in the presence of a strong base such as sodium ethoxide. The esters undergo self-condensation in the basic medium to form beta-keto esters.

A minimum of one reagent must have an alpha hydrogen and be capable of forming an enolate anion following deprotonation in the Claisen condensation reaction.

The base must also avoid nucleophilic substitution reactions or nucleophilic addition with a carbonyl functional group carbon of ester in order to complete the reaction.

The sodium alkoxide, which is the conjugate base of the alcohol to be formed since it is regenerated, is a suitable base for this reaction.

Another criterion, as in the case of ethyl and methyl esters, is that the alkoxy portion of the ester acts as a good leaving group.

4. Benzoin condensation

On heating in the presence of ethanolic KCN, two molecules of aromatic aldehyde (such as benzaldehyde) condense to form benzoin. The cyanide ion in the catalyst functions as a good nucleophilic attacker, promoting the intermediate's nucleophilicity while simultaneously acting as a good leaving group.

5. Esterification

Esterification is another major subtopic under condensation. Esterification is a type of condensation reaction in which an ester is formed from the reaction product of an alcohol and a carboxylic acid. Because of the water molecule released in the reaction, it is classified as a condensation reaction. A strong acid, usually sulfuric acid, serves as the catalyst in this process.

Practice problems:

Q.1(B)
(C) water
(D)

Answer: (A)

Solution:We must identify the reagent used for acetone condensation(aldol condensation reaction). We already know that a base is used as a catalyst in the aldol condensation reaction. The base is barium hydroxide . As a result, it should be used in the acetone condensation reaction.

Q.2. When an enol or an enolate ion interacts with a carbonyl compound to form a -hydroxyaldehyde or -hydroxyketone, which is then dehydrated to yield a -unsaturated carbonyl compounds, which condensation occurs?

(A) Aldol condensation

(B) Claisen reduction

(C) Henry condensation

(D) Knoevenagel condensation

Answer: (A)

Solution:Aldol condensation occurs when an enol or an enolate ion combines with a carbonyl compound to form a -hydroxyaldehyde or -hydroxyketone (an aldol reaction), which is then dehydrated to form a -unsaturated carbonyl compound.

Q.3. Condensation reaction is the reverse of which of the following reaction?

(A) lock and key hypothesis

(B) oxidation

(C) hydrolysis

(D) glycogen formation

Answer: (C)

Solution:Condensation reaction is a reaction in which two reactants combine to generate a single product consisting of simple molecules such as etc. The formation of a peptide bond from two amino acids is a simple example of condensation. The hydrolysis reaction is the reverse of the condensation reaction, in which a chemical entity is split into two parts by the action of a polar water molecule, which divides into hydroxide and hydrogen ions.

Q.4. The condensation reaction always produces complex sugar (disaccharide or polysaccharide) and which of the following?

(A) amino acids

(B) lipids

(C) water

(D) maltose

Answer: (C)

Solution:Condensation reactions always produce complex sugar (disaccharide or polysaccharide) and water.

Frequently asked questions(FAQs):

What are the types of condensation reactions?

Answer:There are two types of Condensation Reaction.

1. Intramolecular Condensation - Two functional groups of the same molecule react to remove simple molecules in this process.
2. Intermolecular Condensation - This reaction occurs when two separate molecules of the same or different substances come together to react and simple molecules are released.

What is the main difference between Aldol and Claisen condensation?

Answer: Both the Claisen condensation process and the aldol condensation reaction are organic condensation reactions that involve the addition of enolates to organic molecules. The aldol condensation process, on the other hand, includes the addition of enolates to ketones or aldehydes, whereas the Claisen condensation reaction involves the addition of enolates to esters.

Why is condensation reaction known as dehydration synthesis?

Answer:A condensation reaction is a type of chemical reaction in organic chemistry in which two molecules join to produce a single molecule, usually with the loss of a minor molecule such as water. The reaction is also known as a dehydration synthesis if water is lost.

What exactly is the difference between hydrolysis and dehydration synthesis?

Answer: The main difference between dehydration synthesis and hydrolysis is that dehydration synthesis produces a large molecule from smaller molecules, whereas hydrolysis produces smaller molecules from a large molecule.