Note on Disproportionation Reaction Examples

A disproportionation reaction is just a chemical process in which a molecule is converted into two or more different products, usually a redox reaction. In a redox reaction, the organism is oxidised and reduced at the same time, yielding at least two distinct products.

Disproportion:

Redox reactions include the reduction from one reactant as well as the oxidation of another, resulting in the reduction of one chemical while the oxidation of another. However, similar to dual-purpose touch screens, there exist processes in which a molecule, atom, or ion can be oxidised and reduced at the same time. 

Examples:

1. When exposed to UV light, mercury(I) chloride disproportionates:

2. Phosphorous acid decomposes into phosphoric acid & phosphine when heated:

3. Disproportionation is a term used to describe desymmetrisation processes, such as the heat breakdown of bicarbonate:

In this acid-base process, the oxidation numbers stay constant. This is also known as autoionization.

Radical disproportionation is another type of disproportionation, wherein the two radicals combine to generate an alkane and an alkene.

4. Sodium chloride, sodium chlorate, and water are formed when chlorine gas combines with dilute sodium hydroxide. This reaction’s ionic equation is as follows:

5. Disproportionation occurs during the decomposition of several interhalogen chemicals. Disproportionation of bromine fluoride produces bromine trifluoride and bromine.

6. The enzyme superoxide dismutase catalyses the dismutation of the superoxide free radical towards hydrogen peroxide and oxygen in biological systems:

In the superoxide free radical anion, oxygen has an oxidation state of 1/2, 1 in hydrogen peroxide, and 0 in dioxygen.

An aldehyde is transformed into alcohol as well as a carboxylic acid in the Cannizzaro reaction. The equivalent ester is the organic redox reaction resulting in the related Tishchenko reaction. A peroxide is transformed into a ketone and alcohol in the Kornblum–Delamare rearrangement.

7. Nitrogen dioxide has an oxidation state of +4, but when it combines with water, it creates nitric acid & nitrous acid, which have oxidation states of +5 and +3, respectively:

8. Acid hydrolysis converts dithionite to thiosulfate & bisulfite:

9.Hypophosphorous acid dissociation

 decomposes into a colourless gas called phosphine and phosphorous

In this case, the phosphorus atom is in the +1-oxidation state . This phosphorus gets to oxidized to , where its oxidation state increases from +1 to +3. The identical phosphorus atom, on the other hand, is reduced. Its oxidation state drops from +1 to -3 at this point.2. Disproportionation reaction of chlorine

i) Chlorine becomes sodium chloride when it combines with a cold, dilute solution of sodium hydroxide , sodium chloride , and water .

The oxidation state of the chlorine atom in the reactant is 0. It undergoes oxidation to +1 in and reduction to -1 in .

ii) Chlorine gas is converted to sodium chlorate when it passes through a heated, concentrated solution of sodium hydroxide (NaOH).

Here, the chlorine that atom with oxidation state 0  reaches +5 in NaClO3 and -1 in .

Desymmetrisation Reactions

The change of a molecule that results in the loss of one or more symmetry components is known as desymmetrization in stereochemistry. The introduction of chirality is a common use of this family of reactions.

Formally, such conversions necessitated the removal of an incorrect rotation axis. Desymmetrisations, in other words, turns prochiral precursors into chiral products.

Example:

Epoxides, diols, dienes, and particularly carboxylic acid anhydrides are common substrates.

The conversion of cis-3,5-diacetoxycyclopentene to monoacetate is one example. The planes of symmetry in the precursor become lost in this transition, and the result is asymmetric. Desymmetrisation isn’t commonly thought to be advantageous in and of itself.

Enantioselective desymmetrisation, on the other hand, produces a valuable result. The enzyme cholinesterase is used in this reaction.

In another case, asymmetric deprotonation of asymmetrical cyclic imide yields a chiral product with excellent enantioselectivity.

Transfer hydrogenation converts benzyl  into one enantiomer of hydroxybenzoic:

The precursor benzyl has symmetry, and the product is symmetric.

Citric acid is also an asymmetric molecule that can be desymmetrized by partial methylation.

Radical Disproportion:

Inorganic chemistry, radical disproportionation refers to a set of reactions in which twin radicals react to produce two non-radical products. Radicals are reactive atoms or molecules with an unpaired electron or electrons in an open shell, as described in chemistry.

Disproportionation via a radical mechanism

One molecule functions as an acceptor, while the other works as a donor, in radical disproportionation reactions. The acceptor takes a hydrogen atom as the donor molecule undergoes an elimination process to produce a double bond in the most typical disproportionation reactions.

Conclusion:

A disproportionation reaction occurs when an element is both oxygenated and reduced in the same process. This is determined by comparing the oxidation state of the element at the start of the reaction to what it does in the two different products as a result; if the oxidation number has continued to increase (i.e. the element has lost electrons), the element has been already oxidised, and if it has decreased (i.e. the element has gained electrons), the element has already been reduced.