Metathesis (chemistry)

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Metathesis, an exchange reaction, or a double replacement reaction is a chemical reaction in which parts of two reacting structures swap places; i.e. a reaction of the type:

AB + CD → AD + CB

where A, B, C and D represent molecules or groups of molecules. The exchange can be thought of as "switching dance partners".

Unlike single displacement reactions, which are always redox, double displacement reactions never feature a redox process.

Contents 1 Olefin metathesis 2 Aqueous metathesis involving inorganic salts 3 Neutralization reactions 4 Acids and carbonates 5 Further reading

[edit] Olefin metathesis

Main article: olefin metathesis

One of the most important new reactions in organic chemistry is olefin metathesis (often called simply metathesis), and the related alkyne metathesis. In olefin metathesis, a metal catalyst causes the two halves of an olefin to switch places, for example:

R¹CH=CH₂ + R²CH=CH₂ → R¹CH=CHR² + H₂C=CH₂

The 2005 Nobel Prize in Chemistry was awarded to Yves Chauvin (France), Richard R. Schrock (USA), and Robert H. Grubbs (USA) for the development of the metathesis method in organic synthesis.

[edit] Aqueous metathesis involving inorganic salts

Metathesis reactions can occur between two inorganic salts when one product is insoluble in water, driving the reaction forward, as in the following examples:

AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)

2AgNO₃(aq) + CaCl₂(aq) → 2AgCl(s) + Ca(NO₃)₂(aq)

CuSO₄(aq) + 2NaCl(aq) → CuCl₂(s) + Na₂SO₄(aq)

This type of reaction is also called double displacement.

One of the compounds formed is usually a precipitate, an insoluble gas that bubbles out of the solution or an insoluble solid, or a molecular compound, usually water. Since one of these conditions must always be met, a solubility chart (or general knowledge of solubility rules) can be used in advance to predict whether two aqueous reactants will react or

[edit] Neutralization reactions

A neutralization reaction is a specific type of double displacement reaction. Neutralization occurs when equal amounts of acid react with equal amounts of a base. A neutralization reaction creates a solution of salt and water, for example:

HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)

[edit] Acids and carbonates

Another subcategory of this reaction type features acids reacting with carbonates/bicarbonates. These reactions always yield carbonic acid as a product, which in turn automatically decomposes into carbon dioxide and water. An example below is the common science fair "volcano" reaction - acetic acid with sodium bicarbonate:

CH₃COOH (aq) + NaHCO₃(s) → CH₃COONa(aq) + CO₂(g) + H₂O(l)

[edit] Further reading

• R. H. Grubbs (Ed.), Handbook of Metathesis, Wiley-VCH, Weinheim, 2003.