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Metathesis (chemistry)
Encyclopedia
Salt 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. This is represented by the general reaction scheme:
These chemical species can either be ionic or covalent. When referring to precipitation reactions between solution
s of ions in inorganic chemistry, these were formerly referred to as double displacement or double replacement reactions
, and these terms are still encouraged. In older literature, the term double decomposition is frequently encountered. It seems that the term double decomposition is more specifically used when at least one of the substances does not dissolve in the liquor, as the ligand or ion exchange takes place in the solid state of the reactant, i.e. AX(aq) + BY(s) → AY(aq) + BX(s).
reacts with an equal amount of a base
. A neutralization reaction creates a solution of a salt and water
. For example, hydrochloric acid
reacts with sodium hydroxide to produce salt
and water
:
salt
s 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:
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.
(s) + 2 (s) → (aq) + 2CuOH (s)
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
:
Chemical bond
A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...
between the two reacting chemical species
Chemical species
Chemical species are atoms, molecules, molecular fragments, ions, etc., being subjected to a chemical process or to a measurement. Generally, a chemical species can be defined as an ensemble of chemically identical molecular entities that can explore the same set of molecular energy levels on a...
, which results in the creation of products with similar or identical bonding affiliations. This is represented by the general reaction scheme:
- AX + BY → BX + AY
These chemical species can either be ionic or covalent. When referring to precipitation reactions between solution
Solution
In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...
s of ions in inorganic chemistry, these were formerly referred to as double displacement or double replacement reactions
Chemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...
, and these terms are still encouraged. In older literature, the term double decomposition is frequently encountered. It seems that the term double decomposition is more specifically used when at least one of the substances does not dissolve in the liquor, as the ligand or ion exchange takes place in the solid state of the reactant, i.e. AX(aq) + BY(s) → AY(aq) + BX(s).
Neutralization
A neutralization reaction is a specific type of double displacement reaction. Neutralization occurs when an acidAcid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
reacts with an equal amount of a base
Base (chemistry)
For the term in genetics, see base A base in chemistry is a substance that can accept hydrogen ions or more generally, donate electron pairs. A soluble base is referred to as an alkali if it contains and releases hydroxide ions quantitatively...
. A neutralization reaction creates a solution of a salt and water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
. For example, hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
reacts with sodium hydroxide to produce salt
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...
and water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
:
- HCl (aq) + NaOH (aq) → NaCl (aq) + (l)
Aqueous metathesis (precipitation)
Metathesis reactions can occur between two inorganicInorganic chemistry
Inorganic chemistry is the branch of chemistry concerned with the properties and behavior of inorganic compounds. This field covers all chemical compounds except the myriad organic compounds , which are the subjects of organic chemistry...
salt
Salt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
s when one product is insoluble in water, driving the reaction forward. For example, the precipitation of silver chloride
Silver chloride
Silver chloride is a chemical compound with the chemical formula AgCl. This white crystalline solid is well known for its low solubility in water . Upon illumination or heating, silver chloride converts to silver , which is signalled by greyish or purplish coloration to some samples...
from a mixture of silver nitrate
Silver nitrate
Silver nitrate is an inorganic compound with chemical formula . This compound is a versatile precursor to many other silver compounds, such as those used in photography. It is far less sensitive to light than the halides...
and sodium chloride causes sodium nitrate
Sodium nitrate
Sodium nitrate is the chemical compound with the formula NaNO3. This salt, also known as Chile saltpeter or Peru saltpeter to distinguish it from ordinary saltpeter, potassium nitrate, is a white solid which is very soluble in water...
to be left in solution:
- (aq) + NaCl (aq) → AgCl (s) + (aq)
The formation of an insoluble gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
that bubbles out of the solution, or a molecular compound such as water, also drives the reaction to completion. Therefore, a solubility chart
Solubility chart
A blue solubility chart refers to a chart with a list of ions and how, when mixed with other ions, they can become precipitates or remain aqueous. The following chart shows the solubilities of various compounds at a pressure of 1 atm and at room temperature...
(or general knowledge of solubility rules) can be used to predict whether two aqueous solutions will react. HSAB theory
HSAB theory
The HSAB concept is an acronym for 'hard and soft acids and bases. Also known as the Pearson acid base concept, HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways....
can also be used to predict the products of a metathesis reaction.
Aqueous metathesis (double decomposition)
The reactants need not to be dissolved for metathesis reactions to take place. An example of this is the formation of barium thiocyanate when boiling a mixture of copper(I)thiocyanate and barium hydroxide in water:(s) + 2 (s) → (aq) + 2CuOH (s)
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 dioxideCarbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
and water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
. 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
Acetic acid
Acetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...
with sodium bicarbonate
Sodium bicarbonate
Sodium bicarbonate or sodium hydrogen carbonate is the chemical compound with the formula Na HCO3. Sodium bicarbonate is a white solid that is crystalline but often appears as a fine powder. It has a slightly salty, alkaline taste resembling that of washing soda . The natural mineral form is...
:
- (aq) + (s) → (aq) + (g) + (l)
See also
- Single displacement reactionSingle displacement reactionA single-displacement reaction, also called single-replacement reaction, is a type of oxidation-reduction chemical reaction when an element or ion moves out of one compound and into another. This is usually written as...This will occur if A is more reactive than B...
- Alkane metathesisAlkane metathesisAlkane metathesis is a chemical reaction in which alkanes are rearranged to give longer or shorter alkane products. It is similar to olefin metathesis, except that olefin metathesis cleaves and recreates a carbon-carbon double bond, but alkane methathesis operates on a carbon-carbon single...
- Olefin metathesisOlefin metathesisOlefin metathesis or transalkylidenation is an organic reaction that entails redistribution of alkylene fragments by the scission of carbon - carbon double bonds in olefins . Its advantages include the creation of fewer sideproducts and hazardous wastes. Yves Chauvin, Robert H. Grubbs, and Richard R...
- Alkyne metathesisAlkyne metathesisAlkyne metathesis is an organic reaction involving the redistribution of alkyne chemical bonds. This reaction is closely related to olefin metathesis. Metal-catalyzed alkyne metathesis was first described in 1968 by Bailey, et al. The Bailey system utilized a mixture of tungsten and silicon oxides...
Further reading
- R. H. Grubbs (Ed.), Handbook of Metathesis, Wiley-VCH, Weinheim, 2003.
- K. Grela (Ed.), "Progress in metathesis chemistry", Thematic Series in the Open AccessOpen access journalOpen access journals are scholarly journals that are available online to the reader "without financial, legal, or technical barriers other than those inseparable from gaining access to the internet itself." Some are subsidized, and some require payment on behalf of the author.Subsidized journals...
Beilstein J. Org. Chem.