Disproportionation

Sometimes, one kind of stuff splits apart. It turns into two new things.

One thing can become two different things. This can happen in a lab. It can also happen in nature.

Tiny bugs use this to live. They turn one thing into others to get energy. This helps them grow.

Heat can make this happen too. Light can make it happen. Even water can do this.

It is a way for things to change. It makes the world very busy.

In chemistry, one kind of change is called disproportionation. This happens when one substance turns into two new things. These two new things are different. One has a higher oxidation state. The other has a lower oxidation state. Oxidation states are just ways to track electrons.

Many things can cause this change. Heat can make it happen. Light can cause it too. For example, mercury chloride changes when UV light hits it. Phosphorus acid changes when it is heated to 200°C. It turns into phosphoric acid and phosphine.

Tiny living things use this to stay alive. Some bacteria use sulfur to get energy. They do this in the mud at the bottom of oceans. This process helps scientists study the Earth's past.

There is also an opposite way. This is called comproportionation. This is when two different things join to make one thing. The Claus reaction is one example. It uses sulfur gases to make solid sulfur. This is used in oil plants.

In chemistry, there is a special way that substances change. It is called disproportionation, or sometimes dismutation. This happens during a redox reaction. In this reaction, one compound starts at an intermediate oxidation state. An oxidation state is a way to track electrons in a molecule. During the change, that one compound turns into two different compounds. One new compound has a higher oxidation state. The other new compound has a lower oxidation state.

This change happens in many different ways. Sometimes, heat causes the reaction to start. For example, heating phosphorous acid to 200°C creates phosphoric acid and phosphine. Other times, light can trigger the change. Mercury(I) chloride will disproportionate when it is hit by UV-irradiation. Even tiny living things use this process to survive. In our bodies, an enzyme called superoxide dismutase helps change superoxide free radicals into hydrogen peroxide and oxygen.

Scientists have studied these changes for a long time. One of the first reactions studied in detail involved tartrates. A scientist named Johan Gadolin examined this in 1788. He wrote about his findings in a Swedish paper. He later published more work on the subject in 1790. His early work helped us understand how these molecules split apart.

There are many specific examples of this in science. Chlorine gas reacts with sodium hydroxide to make sodium chloride, sodium chlorate, and water. In this case, the chlorine starts at an oxidation state of 0. It ends up as -1 in one ion and +5 in another. Another example is the Boudouard reaction. This is when carbon monoxide turns into carbon and carbon dioxide. This reaction is used in the HiPco method to make carbon nanotubes.

Sometimes, we see the exact opposite of this process. The opposite is called comproportionation. This is when two different things join to make one new thing. One famous example is the Claus reaction. This reaction uses hydrogen sulfide and sulfur dioxide to make solid sulfur and water. Oil refinery plants use the Claus process to remove sulfur from gases. This makes the sulfur easier to store, move, and reuse.

In the field of chemistry, disproportionation is a specific type of redox reaction. It is also frequently referred to as dismutation, which is the French term for this process. During this reaction, a single compound with an intermediate oxidation state transforms into two distinct products. One of these products possesses a higher oxidation state, while the other has a lower oxidation state. This process effectively splits a single substance into two different chemical identities. It is a fundamental way that molecules redistribute their electrons to reach new states.

To understand the mechanism, one must look at how electrons move. In a redox reaction, oxidation and reduction occur simultaneously. In disproportionation, the starting molecule acts as both the oxidizing agent and the reducing agent. This means some parts of the molecule lose electrons, while other parts gain them. This causes the single reactant to divide into two different substances. The reverse of this process is called comproportionation, or symproportionation. In comproportionation, a compound in an intermediate state is formed from precursors with lower and higher oxidation states.

There are several distinct types of these reactions. One type is radical disproportionation, which involves two radicals. In this version, the radicals react to form an alkene and an alkane. Another form is desymmetrizing reactions, which can include molecular autoionization. An example of this is the self-ionization of water. Some scientists use the term redistribution for reactions where only ligand exchange occurs without any redox change. An example of such a redistribution reaction is the Schlenk equilibrium.

The study of these reactions has a long history in science. The first disproportionation reaction to be studied in great detail involved tartrates. A scientist named Johan Gadolin examined these substances in 1788. He published his initial findings in a Swedish paper that year. He later provided more detailed research in 1790. His work laid the early groundwork for understanding how these chemical changes occur.

Many specific chemical examples demonstrate this principle across different elements. Chlorine gas reacts with concentrated sodium hydroxide to produce sodium chloride, sodium chlorate, and water. In this reaction, the chlorine starts at an oxidation state of 0. It ends up as -1 in the chloride ion and +5 in the chlorate ion. Another example is the Boudouard reaction, where carbon monoxide disproportionates into carbon and carbon dioxide. This specific reaction is utilized in the HiPco method to produce carbon nanotubes.

Disproportionation is also vital in the world of biology and biochemistry. In 1937, Hans Adolf Krebs confirmed that certain bacteria perform the anaerobic dismutation of pyruvic acid. This process turns pyruvic acid into lactic acid, acetic acid, and carbon dioxide. This is a key part of fermentation reactions. In cellular respiration, electrons move from a donor to an acceptor. In fermentation, the substrate molecule itself acts as both the donor and the acceptor. This makes fermentation a type of disproportionation.

Microorganisms also use sulfur disproportionation, often called microbial sulfur disproportionation or MSD. This is a type of energy metabolism involving inorganic sulfur compounds. This process often happens alongside the reduction of sulfate in certain bacteria. Geoscientists study sulfur isotopes in sediments to learn about the Earth's past environments. They look at these isotopes to understand the redox conditions of ancient oceans. While scientists once thought sulfate reduction caused large isotopic shifts, they now look to disproportionation to explain these changes.

Finally, these reactions connect to large-scale industrial processes. The Claus reaction is a famous example of comproportionation, which is the inverse of disproportionation. It involves reacting hydrogen sulfide and sulfur dioxide to create elemental sulfur and water. This is used in the Claus process within oil refinery plants. This process is essential for the desulfurization of gases. By removing sulfur, the industry creates solid elemental sulfur that is easy to store, transport, and reuse.