Question

What is disproportionation reaction? Explain by an example.

Answer 1

Hint: Disproportionation reaction is also known as dismutation reaction. It is a type of redox reaction. A single reactant undergoes reduction as well as oxidation to give two different products.

Complete Solution :
Disproportion reaction:
- Disproportionation reaction is a special type of redox reaction in which a single reactant simultaneously undergoes oxidation and reduction.
- Disproportionation reaction is also called dismutation reaction.
- The reactant molecules act as both oxidizing and reducing agents.
- Disproportionation reaction is a unique type of reaction in which the same element simultaneously gains and loses electrons to form two different products.
- The reactant with intermediate oxidation state, gives two new compounds, one with higher oxidation state and the other with lower oxidation state.

Examples of disproportionation reaction:
- Disproportionation reaction of Copper (I) chloride.
$2CuCl\to CuC{{l}_{2}}+Cu$
After allowing the solution to stand for long hours, the solution becomes blue with a pink deposit t the bottom of the beaker. Analysis of the product reveals that the formation of Copper (metal) and Copper (II) chloride.
$CuCl\to +1$ Oxidation state
$Cu\to 0$ Oxidation state
$CuC{{l}_{2}}\to +2$ Oxidation state
Copper (I) chloride acts as both reducing and oxidizing agent. From Copper (I) chloride to Copper (II) chloride, the oxidation state increases from +1 to +2. When the Copper (I) chloride is converted to copper metal, the oxidation state decreases from +1 to 0.

- Mercury (I) chloride disproportionate upon UV-irradiation:
$H{{g}_{2}}C{{l}_{2}}\to HgC{{l}_{2}}+Hg$
$H{{g}_{2}}C{{l}_{2}}\to +1$ Oxidation state
$HgC{{l}_{2}}\to +2$ Oxidation state
$Hg\to 0$ Oxidation state.

Additional Information:
There are other types of redox reactions other than disproportionation. They are:
- Decomposition reaction
- Combination reaction
- Displacement reaction

Note: The reverse of disproportionation reaction is known as comproportionation or synproportionation. When compound of intermediate oxidation state is formed from precursors of lower and higher oxidation state, then it is called comproportionation reaction.