A salt metathesis reaction is a chemical process involving the exchange of bonds between two reacting chemical species which results in the creation of products with similar or identical bonding affiliations.
[1] This reaction is represented by the general scheme: Typical examples are the reactions between oxysalts and binary compounds such as salts, hydrohalic acids and metal hydroxides:
The bond between the reacting species can be either ionic or covalent.
In older literature, the term double decomposition is common.
The term double decomposition is more specifically used when at least one of the substances does not dissolve in the solvent, as the ligand or ion exchange takes place in the solid state of the reactant.
For example: Salt metathesis is a common technique for exchanging counterions.
The choice of reactants is guided by a solubility chart or lattice energy.
HSAB theory can also be used to predict the products of a metathesis reaction.
Metathesis reactions can occur between two inorganic salts when one product is insoluble in water.
For example, the precipitation of silver chloride from a mixture of silver nitrate and cobalt hexammine chloride delivers the nitrate salt of the cobalt complex: The reactants need not be highly soluble for metathesis reactions to take place.
For example barium thiocyanate forms when boiling a slurry of copper(I) thiocyanate and barium hydroxide in water: Metal complexes are alkylated via salt metathesis reactions.
Illustrative is the methylation of titanocene dichloride to give the Petasis reagent:[4] The salt product typically precipitates from the reaction solvent.
A neutralization reaction occurs when an acid reacts with an equal amount of a base.
One example, hydrochloric acid reacts with disodium iron tetracarbonyl to produce the iron dihydride: Reaction between an acid and a carbonate or bicarbonate salt yields carbonic acid, which spontaneously decomposes into carbon dioxide and water.
For example, a common, science-fair "volcano" reaction involves the reaction of hydrochloric acid with sodium carbonate: In contrast to salt metathesis reactions, which are driven by the precipitation of solid salts, are salt-free reductions, which are driven by formation of silyl halides, Salt-free metathesis reactions proceed homogeneously.