Disproportionation

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Disproportionation or dismutation disproportionation is any chemical reaction of the type A + A → A' + A", where A, A' and A" are different chemical species. For example: 2 ArH⁺ → ArH + ArH²⁺ The reverse of disproportionation is called comproportionation. This definition comes from IUPAC ([1]) While the most common type is a redox reaction, other types are possible. For example: 2H₂O → H₃O⁺ + OH^- is also a disproportionation.

[edit] Examples

• Chlorine (Cl₂) reacts with sodium hydroxide to form sodium chloride, sodium chlorate and water. The ionic equation for this reaction is as follows:

3Cl₂ + 6OH⁻ → 5Cl⁻ + ClO₃⁻ + 3H₂O

In the above equation, the initial oxidation number of chlorine is 0. In the products, Cl⁻ has an oxidation number of −1, having been reduced, whereas the oxidation number of chlorine in the chlorate ion is +5, indicating that it has been oxidized. It should be noted that there is no change of oxidation state for the sodium ion.

• The catalysis of hydrogen peroxide to water and oxygen by the enzyme catalase occurs in two stages:

H₂O₂ + Fe(III)-E → H₂O + O=Fe(IV)-E (oxidation of Fe(III) to Fe(IV))

H₂O₂ + O=Fe(IV)-E → H₂O + Fe(III)-E + O₂ (reduction of Fe(IV) back to Fe(III))

(Where Fe-E represents the iron centre of the heme group attached to the enzyme.)

• C₄H₄ reacts with itself to form C₆H₆ and C₂H₂.

2C₄H₄ → C₆H₆ + C₂H₂

• In the Cannizzaro reaction an aldehyde is converted into an alcohol and a carboxylic acid. In the related Tishchenko reaction the organic redox reaction product is the corresponding ester. In the Kornblum–DeLaMare rearrangement a peroxide is converted to a ketone and an alcohol.

[edit] External link

• Glossary entry