Kolbe electrolysis, sometimes known as the Kolbe reaction, is a type of organic reaction named after Hermann Kolbe. It's best for making symmetrical dimers, but it can also be used to make unsymmetrical dimers when combined with a mixture of two carboxylic acids.
Here, we will discuss the method of Kolbe electrolysis, the mechanism of electrolysis, and how Kolbe’s reaction is used in the preparation of alkane and acetic acid.
Kolbe's Electrolytic Method
The Kolbe reaction is a decarboxylative dimerization of two carboxylic acids in its formal form (or carboxylate ions). The general reaction is
General Reaction of Kolbe's Electrolysis
Mechanism of the Above Reaction:
Two molecules of carboxylate ions lose two electrons and two molecules of carbon dioxide to form two alkyl free radicals, which then join together to form an alkane.
Mechanism of Kolbe's Reaction
Let us now define electrolysis. The word "lysis" means "to separate or break," so electrolysis would be defined as "electric breakdown." Electrolysis is a method of causing a non-spontaneous chemical reaction to occur using electrical energy.
Electrolysis is a chemical and industrial process that uses the direct electric current (DC) to drive a chemical reaction that would otherwise be non-spontaneous. The use of an electrolytic cell in the commercial separation of elements from naturally occurring sources such as ores is important. The decomposition potential is the voltage needed for electrolysis.
The Process of Electrolysis
Faraday’s Law of Electrolysis
The amount of product created by the passage of an electric current (moles) is stoichiometrically equal to the quantity of electrons provided (moles).
The stoichiometry of the reaction, the size of the current flowing, and the time during which the current flows are used to compute the amount of product generated during an electrolysis operation.
Let us now explain Kolbe's reaction. It is sometimes known as the Kolbe Schmitt reaction, after Hermann Kolbe and Rudolf Schmitt, and is an addition reaction. The phenoxide ion is formed when phenol reacts with sodium hydroxide. The phenoxide ion generated in electrophilic aromatic substitution processes is more reactive than phenol. As a result, the weak electrophile carbon dioxide undergoes an electrophilic substitution process. Ortho-hydroxybenzoic acid is the main product (salicylic acid). Kolbe's reaction is another name for this process.
Kolbe's Reaction of Preparation of Alkane
Electrolysis is the process of electrolyzing a concentrated sodium salt of a carboxylic acid. In one of the products, the alkane is produced at the anode. This reaction of the formation of alkane from a derivative of the carboxylic acid is also known as Kolbe’s reaction.
Kolbe’s Reaction to Get Alkane
Kolbe Electrolysis Mechanism
Kolbe electrolysis reaction has the following mechanism:
The sodium salt of carboxylic acid undergoes electrolysis to form alkane as the major product and carbon dioxide water and caustic soda as byproducts.
An oxidation reaction occurs at the anode, which results in the loss of carbon dioxide and the formation of two methyl free radicals which then react among themselves forming ethane.
Reduction occurs at the anode which results in the formation of two hydroxide ions as well as two hydrogen free radicals which react among themselves, forming hydrogen molecules.
Mechanism of Kolbe’s electrolysis.
Synthesis of Acetic Acid by Kolbe
For the first time in 1845, German chemist Hermann Kolbe produced or synthesised acetic acid from inorganic components. He combined chlorine and carbon disulfide to produce carbon tetrachloride. The electrolytic reduction to acetic acid was then followed by heat decomposition to tetrachloroethylene and aqueous chlorination to trichloroacetic acid. Only hydrocarbons were employed in the inorganic chemicals he used. As a result, Kolbe was the first to make acetic acid from carbon, hydrogen, and oxygen.
Synthesis of Acetic Acid by Kolbe’s Reaction
At the anode of Kolbe's electrolytic method, the electrolysis of an aqueous solution of a potassium or sodium salt of a carboxylic acid produces an alkane with an even number of carbon atoms. The decarboxylation of the sodium salt of fatty acid occurs in this reaction. A two-stage radical process is involved in the reaction mechanism, namely, electrochemical decarboxylation produces a radical intermediate, which combines to form a covalent bond. This reaction is used in the formation of alkanes and acetic acid from carboxylic acid derivatives, which undergoes an electrolytic mechanism.