Metathesis is a molecular process involving the exchange of bonds between the two reacting chemical species, which results in the creation of products with similar or identical bonding affiliations.[1] This is represented by the general reaction scheme:
- AX + BY → AY + BX
These chemical species can either be ionic or covalent. When referring to precipitation reactions between solutions of ions in inorganic chemistry, these were formerly referred to as double displacement or double replacement reactions, though these terms are still encouraged.[citation needed]
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Types of reaction
Neutralization
A neutralization reaction is a specific type of double displacement reaction. Neutralization occurs when an acid reacts with an equal amount of a base. A neutralization reaction creates a solution of salt and water. For example, hydrochloric acid reacts with sodium hydroxide to produce salt and water:
- HCl (aq) + NaOH (aq) → NaCl (aq) + H2O (l)
Aqueous metathesis (precipitation)
Metathesis reactions can occur between two inorganic salts when one product is insoluble in water, driving the reaction forward. For example, the precipitation of silver chloride from a mixture of silver nitrate and sodium chloride causes sodium nitrate to be left in solution:
- AgNO3 (aq) + NaCl (aq) → AgCl (s) + NaNO3 (aq)
The formation of an insoluble gas that bubbles out of the solution, or a molecular compound such as water, also drives the reaction to completion. Therefore, a solubility chart (or general knowledge of solubility rules) can be used to predict whether two aqueous solutions will react. HSAB theory can also be used to predict the products of a metathesis reaction.
Acid and carbonates
A subcategory of aqueous metathesis reactions is the reaction of an acid with a carbonate or bicarbonate. Such a reaction always yields carbonic acid as a product, which spontaneously decomposes into carbon dioxide and water. The release of carbon dioxide gas from the reaction mixture drives the reaction to completion. For example, a common, science-fair "volcano" reaction involves the reaction of acetic acid with sodium bicarbonate:
- CH3COOH (aq) + NaHCO3 (s) → CH3COONa (aq) + CO2 (g) + H2O (l)
Olefin metathesis
An important and influential reaction within organic chemistry, which involves the principle of metathesis is the olefin metathesis reaction developed by Yves Chauvin, Richard R. Schrock and Robert H. Grubbs, who shared a Nobel Prize in Chemistry in 2005.
The principle of olefin metathesis is that an alkene double bond is cleaved and redistributed alongside the redistribution of an alkylidene under the presence of catalytic metals, such as ruthenium, nickel, or tungsten. It has several commercially significant applications, and it is especially useful due to the relatively small amounts of side products and hazardous waste products.
In this context, the otherwise abstract concepts of metathesis are especially well-visualized in the unique diplomas which were crafted for King Carl XVI Gustaf to present to the three chemists who shared the Nobel Prize in 2005.
Intramolecular metathesis of a diene
Ring formation occurs when a diene is used as the starting material. Any size ring is possible to make with metathesis of a diene. For example, in the presence of a metal catalyst, usually Grubbs' catalyst, 4-methyl-1,7-octadiene forms 4-methylcyclohexene. When using terminal alkenes the by-product is always gaseous ethene.[2]
See also
References
- ^ International Union of Pure and Applied Chemistry, (2006). IUPAC Gold Book, Compendium of Chemical Terminology IUPAC Publications
- ^ Janice Gorzynski Smith. Organic Chemistry: Second Ed. 2008. pp 1016-1018.
Further reading
- R. H. Grubbs (Ed.), Handbook of Metathesis, Wiley-VCH, Weinheim, 2003.
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