Kolbe’s Reaction

Kolbe Reaction also known as Kolbe Electrolysis or Kolbe-Schmitt Reaction, named after 19th-century German chemist Hermann Kolbe, is a chemical process significant in Organic Chemistry. Kolbe Reaction is a type of an addition reaction in which Phenol reacts with NaOH to give Phenoxide Ion. It has made a significant impact on organic chemistry, from its early origins in the lab to its modern applications in various scientific fields. Students have to study Kolbe Reaction in Class 12. Let’s learn What is Kolbe Reaction and explore its mechanism, applications, and more in the article.

What is Kolbe’s Reaction?

Kolbe’s Reaction, also known as Kolbe Electrolysis or Kolbe-Schmitt Reaction is a type of addition reaction. In this reaction, when phenol reacts with sodium hydroxide, it forms the phenoxide ion. This ion is more reactive than phenol when it comes to electrophilic aromatic substitution reactions. The phenoxide ion readily undergoes electrophilic substitution reaction with carbon dioxide, a weak electrophile, to produce ortho-hydroxybenzoic acid, also known as salicylic acid.

In simpler terms, the Kolbe Reaction is a process of heating a combination of sodium phenoxide and carbon dioxide under a pressure of 180°C to 200°C to produce salicylic acid.

Related read: Chemical Reactions of Alcohols, Phenols, and Ethers

Mechanism of the Kolbe Reaction

Kolbe Reaction is a chemical process that involves Carboxylation. Carboxylation means adding of carboxyl group to the phenol molecule. The mechanism of Kolbe Reaction is described as follows:

1. The mechanism of Kolbe reaction begins by passing carbon dioxide through sodium phenoxide solution. This results into a chemical reaction. The resultant product of the reaction is heated at a temperature of 125°C under 100 atmospheric pressure. This forms an unstable intermediate compound.
2. The unstable intermediate compound undergoes a change known as proton shift. This change leads to the formation called sodium salicylate.
3. The mixture of sodium salicylate is further treated with sulfuric acid. Later, the ddition of sulfuring acid results in chemical reaction known as acidification and as a result salicylic acid is formed.

Related read:

• Carboxylic acids
• Methods of preparation of Carboxylic acids

Kolbe-Schmitt Reaction Applications

Kolbe Reaction has various practical applications across various industries. Some of them include:

1. Kolbe reaction is used in various pharmaceutical synthesis. For example, Aspirin drug is formed after the synthesis of salicylic acid via the Kolbe Reaction.
2. It is also used in Polymer Industry to synthesis conductive polymers. There polymers are used in the application of electronic devices, sensors, etc.
3. The reaction is used in formation of LED screens, optical devices and materials with unique optical properties.
4. The reaction is used in the formation of organic compounds in the production of dyes and pigments.
5. Kolbe reaction is used in parabens. It is a class of preservatives that are used in variety of products such as cosmetics.

Learn more about Aspirin formula

Kolbe-Schmitt Reaction – FAQs

1. What is Kolbe Schmitt Reaction in Chemistry?

Kolbe’s Reaction is an addition reaction in chemistry in which Phenol react with Sodium Hydroxide to give phenoxide ion.

2. What is the other Name of Kolbe’s Reaction?

Kolbe’s Reaction is also known as Kolbe’s Electrolysis and Kolbe Schmitt Reaction.

3. Which is the Primary Compound used in Kolbe Reaction?

The primary compound used in Kolbe Reaction is phenol. Phenol is an aromatic compound with the formula of C₆H₅OH.

4. Explain Mechanism of Kolbe Reaction.

Below mentioned are the key steps used in the mechanism of Kolbe Reaction:

• The mechanism of Kolbe reaction begins by passing carbon dioxide through sodium phenoxide solution. This results into a chemical reaction. The resultant product of the reaction is heated at a temperation of 125°C under 100 atmospheric pressure. This forms an unstable intermediate compound.
• The unstable intermediate compound undergoes a change known as proton shift. This change leads to the formation called sodium salicylate.
• The mixture of sodium salicylate is further treated with sulfuric acid. Later, the ddition of sulfuring acid results in chemical reaction known as acidification and as a result salicylic acid is formed.

5. What is the Primary Synthesis of Salicylic Acid?

The primary synthesis of salicylic acid begins with phenol compound. It’s chemical reaction is generated as:

2 C₆H₅ONa (Sodium Phenoxide) + 2 CO₂ (Carbon Dioxide) + H₂O (Water) → 2 C₆H₄(OH)COOH (Salicylic Acid)

6. Why CO₂ is used in Kolbe Reaction?

Carbon Dioxide is considered as weak electrophile. It is used in the reaction because nucelophile such as phenoxide ion to attack and form a new bond with the carbon atom in CO_2.

7. Why is NaOH used in the Kolbe’s Reaction?

NaOH is used in chemical reaction to the make the reaction medium basic.

8. Why Methane cannot be Prepared by Kolbe Reaction?

Kolbe’s electrolysis method cannot be used to prepare methane because methane has only one carbon atom. This chemical reaction is suitable for preparing symmetrical alkanes with an even number of carbon atoms.

9. Who discovered Kolbe Reaction?

The Kolbe Reaction is named after 19th-century German chemist Hermann Kolbe and Rudolf Schmitt.

10. What are the Limitations of Kolbe Reaction?

The reaction has seen limited applications owing to extremely poor chemoselectivity and reliance on precious metal electrodes.

11. Can Kolbe Reaction be used for Converting Sodium Acetate to Ethane?

Yes it is possible to convert sodium acetate to ethane using the Kolbe Reaction. This can be done through Kolbe electrolysis process and further the aqueous solution sodium acetate is electrolyzed.