Cannizzaro Reaction for IIT JEE Organic Chemistry

Cannizaro Reaction in organic chemistry is known for its duality and versatility. Cannizzaro’s reaction is named after its discoverer and founder, Stanislao Cannizzaro. The Cannizzaro reaction is a well-known chemical transformation that has fascinated scientists and researchers for generations. In this blog, we will explore the intricate mechanism of the Cannizzaro reaction that underlay redox reaction principles. We will also get to know how Cannizzaro’s reaction has an indelible mark on the chemical world and plays a crucial role in the synthesis of carboxylic acids and alcohols.

What is Cannizzaro’s Reaction?

The Cannizzaro reaction is a chemical transformation in redox chemistry that involves the base-induced disproportionation of two molecules of a non-enolizable aldehyde to yield a carboxylic acid and a primary alcohol. In other words, one molecule of the aldehyde undergoes oxidation to form the corresponding carboxylic acid, while the other molecule undergoes reduction to form the corresponding primary alcohol.

Cannizzaro Reaction

Learn about Balancing Redox Reactions

Examples of Cannizzaro Reaction

The example of cannizzaro reaction is shown in the image below:

Here are a couple of examples where Cannizzaro reaction is used:

• Formaldehyde (Methanal) – CH₂O
• Benzaldehyde – C₆H₅CHO
• Vanillin – C₈H₈O₃
• Syringaldehyde – C₉ H₁₀O₄
• p-Nitrobenzaldeyde – C₇H₅O₃

Mechanism of Cannizzaro Reaction

The mechanism of Cannizzaro reaction is process of getting one molecule of alcohol and one molecule of carbocyclic acid from two molecules of a given aldehyde. Below-mentioned are the steps of mechanics of Cannizzaro Reaction:

Step 1: Nuceophilic Attack

In the very first step, the crbonyl group the aldehyde undergoes nucleophile attack from a nucleophile such as OH. This nucleophile attack produces anion having two negative charges as result.

Step 2: Hydride Transfer

The intermediate formed in step 1 is unstable and act as hydride transfer agent for another aldehyde molecule and reduce it. Thus the another aldehyde group get reduced to alkoxide ion while the intermediate that acted as hydride transfer agent becomes carboxylate anion.

Step 3: Proton Exchange

In the third and the final step, the alkoxide ion formed in step 2 gains proton from water thus resulting in the alcohol as the final product.

After the workup of acid, the carboxylate ion get converted to carboxylic acid. Since, the acid is less basic than water hence, it can’t obtain proton from water.

Crossed Cannizzaro Reaction

The Crossed Cannizzaro Reaction is a variation of Cannizzaro Reation in which two different aldehydes are reacted together and one of them must be non-enolizable. Here is a brief difference between Cannizzaro Reaction and Crossed Cannizzaro Reaction.

Mechanism of Crossed Cannizzaro Reaction

The mechanism of crossed cannizzaro reaction involves the disproportionaion of two different aldeyhdes with one aldehyde acting as a reductant and the other aldehyde acting as an oxident:

• The base reacts with one of the aldehydes and removes a proton, resulting in the formation of an alkoxide anion.
• The alkoxide anion proceeds to attack the carbonyl carbon of the other aldehyde, resulting in the formation of a tetrahedral intermediate.
• As a result of the collapse of the tetrahedral intermediate, a new C-O bond is formed, and a hydride ion is transferred from the reductant aldehyde to the oxidant aldehyde.
• The hydride ion is then protonated by water, forming the corresponding alcohol.
• Additionally, the alkoxide anion that was generated from the reductant aldehyde is also protonated by water, leading to the formation of the corresponding carboxylic acid.

Below is the chemical equation of crossed cannizzaro reaction between formaldehyde and benzaldehyde:

HCHO + PhCHO + NaOH →NaHCO₂ + PhCH₂OH

Cannizzarro vs Crossed Cannizzarro Reaction

The basic comparison between cannizzaro and crossed cannizzaro reaction is mentioned in the table below:

Characterstic	Cannizzaro Reaction	Crossed Cannizzaro Reaction
Type of Reaction	Disproportionantion	Disproportionation
Aldeyhdes	Two same non-enolizable aldehydes	Two different aldehydes are reacted together and one of them must be non-enolizable
Products	Two primary alcholos and carboxyclic acids	One primary alcohol and carboxylic acid
Yield	High	High

Applications of the Cannizzaro Reaction

The Cannizzaro Reaction has a variety of applications in the organic chemistry:

• The Cannizzaro Reaction is used for the synthesis of alcohols such as benzyl, furfuryl, and vanillyl.
• It is also used in the purification of aldehydes.
• The chemical reaction is used in the perfume industry such as synethsis of benzyl alcohol.
• Cannizzaro reaction is also used in the food and beverage industry.
• The Cannizzaro reaction is applied in the adhesives and coating industry where synethesization of furfuryl alcohol is done.

Sample Questions on Cannizzaro Reaction

Question 1: What is Cannizzaro Reaction in organic chemistry?

Answer:

The Cannizzaro reaction is a chemical transformation in redox chemistry that involves the base-induced disproportionation of two molecules of a non-enolizable aldehyde to yield a carboxylic acid and a primary school. In other words, one molecule of the aldehyde undergoes oxidation to form the corresponding carboxylic acid, while the other molecule undergoes reduction to form the corresponding primary alcohol.

Question 2: What are the products formed in the Cannizzaro chemical reaction involving formaldehyde (HCHO)?

Answer:

Balanced chemical equation of Cannizzaro reaction involving formaldehyde (HCHO):

2HCHO(formaldehyde) + 2NaOH(sodium hydroxide) → HCOONa(sodium formate) + CH₃OH(methanol)

Hence the products formed are one molecule of sodium formate and another is methanol.

Question 3: Provide the balanced chemical equation of Cannizzaro reaction involving benzaldehyde.

Answer:

Benzaldeyde can go under the Cannizzaro reaction and following is the chemical equation:

2 C₆H₅CHO (benzaldehyde) + 2 NaOH → C₆H₅COONa (sodium benzoate) + C₆H₅CH₂OH (benzyl alcohol)

Question 4: Discuss some practical applications of the Crossed Cannizzaro Reaction.

Answer:

There are variety of applications the Crossed Cannizzaro reaction. Below-mentioned are some of them:

• The crossed cannizzaro reaction is used for the synthesis of alcohols such as benzyl, furfuryl, and vanillyl.
• It is also used in the purification of aldehydes.
• The chemical reaction is used in the perfume industry such as synethsis of benzyl alcohol.
• It is also used in the food and beverage industry.
• The chemical reaction is applied in the adhesives and coating industry where synethesization of furfuryl alcohol is done.

Question 5: Can ketones undergo the Cannizzaro reaction? Why or Why not?

Answer:

The Cannizzaro reaction requires the aldehyde molecule to have at least one alpha hydrogen for the transfer of a hydride ion to occur. Ketones have two alpha hydrogens, so they cannot donate a hydride ion to another ketone molecule.

FAQs on Cannizzaro Reaction

1. What is Cannizzaro Reaction in Organic Chemistry?

The Cannizzaro reaction is a chemical transformation in redox chemistry that involves the base-induced disproportionation of two molecules of a non-enolizable aldehyde to yield a carboxylic acid and a primary school. In other words, one molecule of the aldehyde undergoes oxidation to form the corresponding carboxylic acid, while the other molecule undergoes reduction to form the corresponding primary alcohol.

2. How many Compounds give Cannizzaro Reaction?

There are six compounds which can give cannizzaro reaction

3. Does Ketone udergoes Cannizzaro Reaction?

Cannizzaro reaction does not usually occur with ketones. There are some instances where ketones give cannizzaro.

4. Is Cannizzaro a Redox Reaction?

Yes, cannizzaro reaction is a redox reaction.

5. What are the Limitations of Cannizzaro Reaction?

Cannizzaro reaction in organic chemistry yield not more than 50% for either acid or alcohol formed.

6. What is the Differnce between Cannizzaro and Crossed Cannizzaro Reaction?

The basic difference between cannizzaro and cross cannizzaro reaction is that cannizzaro reaction uses two same non-enolizable aldehydes while the cross cannizzaro reaction uses two different aldehydes one of them is enolizable.