What is dismutation?

The dismutations also called disproportion reaction any disproportion disproportion), is a type of redox reaction in which an element or chemical species is reduced and oxidized.

Said element starts from an intermediate oxidation state in an amount of two or more and gives rise to at least two other forms with oxidation states different from the initial one, one in a higher oxidation state and another in a lower state.

In dismutation, the same substance is oxidized and reduced. The first dismutation reaction studied in detail was tin dismutation:

2Sn2+ → Sn4+ + sn

Dismutation of hydrogen peroxide

One of the most common examples of a dismutation reaction is decomposition of hydrogen peroxide (hydrogen peroxide) into water and molecular oxygen:

2HtwoANYtwo → 2HtwoOR + ORtwo

In the dismutation of hydrogen peroxide, the oxygen starts from an oxidation state -1, but in the products it is found in an oxidation state -2 (in water) and zero (in molecular oxygen).

That is, the oxygen in the hydrogen peroxide molecule (HtwoANYtwo) is in an intermediate oxidation state, -1, and is reduced to the -2 state to form water (HtwoO), and is also oxidized to the 0 (zero) oxidation state. to form molecular oxygen (Otwo).

The reaction can be outlined in these two steps. First, a molecule of hydrogen peroxide breaks down into molecular oxygen, releasing 2 protons and 2 electrons:

HtwoANYtwo → outwo + 2H+ + 2e−

The two released protons and electrons react with another hydrogen peroxide molecule to form two water molecules:

2H+ + HtwoANYtwo + 2e− → 2HtwoANY

Giving as a final result that the reaction of two molecules of hydrogen peroxide undergoes a dismutation into two molecules of water and one of molecular oxygen:

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2HtwoANYtwo → 2HtwoOR + ORtwo

Other examples of dismutation

Mercury(I) chloride undergoes dismutation under ultraviolet radiation:

HgtwoCltwo → Hg + HgCltwo

Phosphoric acid dismutes by heating into phosphoric acid and phosphine:

4H3PO3 → 3H3PO4 +PH3

The dismutation of superoxide free radicals into hydrogen peroxide and molecular oxygen is a reaction catalyzed in living organisms by the enzyme superoxide dismutase (the oxidation state of oxygen is -1/2 in the superoxide ion, -1 in the hydrogen peroxide, and 0 (zero) ) in molecular oxygen):

2Otwo− + 2H+ → HtwoANYtwo + ORtwo

This dismutation is very important for all aerobic organisms, including humans. In all of them, superoxide dismutase is present to protect against the harmful action of free radicals that are produced in cellular respiration.

There are many other examples of dismutation in biochemistry. For example, in fermentation, a part of the substrate molecule acts as an electron donor and another part as an acceptor, which can be considered a form of dismutation.

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