What is a disproportionation reaction 1

to directory mode

Area of ​​Expertise - General Chemistry

Disproportionation can generally be understood to mean a reaction in which substances of different types are formed from similar reaction partners through decomposition or rearrangement.

Disproportionation is particularly common in redox reactions. Then it is a reaction in which one and the same compound is oxidized and reduced at the same time and the oxidation numbers of several atoms of the same kind change in different directions.

An example is the disproportionation of chlorine (oxidation number of the chlorine atoms in: zero) in sodium hydroxide solution to form chloride (-1) and hypochlorite (+1)

+ 2 → + +

The Cannizzaro reaction is also a disproportionation. Here, 2 aldehyde molecules are formed into a carboxylic acid molecule through oxidation and an alcohol molecule through reduction.

2 → +

Disproportionation of hydrocarbon radicals also occurs particularly frequently:

2 → +

An example of this is the disproportionation of two ethyl radicals in ethylene and ethane. The formal redox reaction takes a back seat, as no new oxidation states are created, but are only regrouped. The focus is on the transfer of hydrogen atoms (in rare cases also other atomic groups), whereby one saturated and one unsaturated molecule are formed from 2 radical molecules. Another example of this reaction is the disproportionation of two polymer radicals (here R are each large chains or substituents). The two unpaired electrons come together with the simultaneous transfer of an H atom to form a π-bonding pair and the chain growth reaction is terminated. When the chain growth is terminated, the disproportionation (here 2 molecules of the size of the radicals are created) competes with the combination reaction (here only 1 molecule of the size of both radicals is created together).

The opposite of disproportionation is generally called comproportionation or synproportionation.

Learning units in which the term is dealt with

phosphorus60 min.

chemistryInorganic chemistryChemistry of the elements

This learning unit gives an overview of the element phosphorus including properties, reaction behavior, detection, occurrence, extraction and use of the element as well as selected compounds.

End group determination20 min.

chemistryMacromolecular ChemistryPolymer analysis

The possibilities and areas of application of end group analysis for determining molar mass are shown. The relationship between the number of end groups per molecule and the course of the polymerization reaction is particularly important here. Various methods for determining end groups are presented.

Oxidation numbers45 min.

chemistryGeneral ChemistryChemical bond

This learning unit looks at ionic bonding from the point of view of oxidation numbers. It describes rules for determining oxidation numbers. It describes how to determine the oxidation numbers of the atoms in compounds. An overview of the oxidation numbers of the main group elements is given. With the help of the oxidation numbers they learn to solve redox reactions.

Saturation of polymer radicals30 min.

chemistryMacromolecular ChemistryReaction mechanisms

Termination reactions and transfers turn polymer radicals into inactive polymer molecules. The radical properties are lost on termination. When transferring, the radical property is transferred to another molecule. Both reactions are presented here in detail and illustrated using the example of styrene polymerization.