Schlenk equilibrium
Encyclopedia
The Schlenk equilibrium is a chemical equilibrium
named after its discoverer Wilhelm Schlenk
taking place in solutions of Grignard reagents.
The process described is an equilibrium between two equivalents of an alkyl or aryl magnesium halide on the left of the equation and on the right side, one equivalent of the dialkyl or diaryl
magnesium compound and magnesium halide salt
. Organomagnesium halides in solution also form dimers and higher oligomer
s, especially at high concentration. Alkyl magnesium chlorides in ether are present as dimers.
The position of the equilibrium is influenced by solvent, temperature, and the nature of the various substituents. It is known that magnesium center in Grignard reagents typically coordinates two molecules of ether such as diethyl ether or tetrahydrofuran
(THF). Thus they are more precisely described as having the formula RMgXL2 where L = an ether. In the presence of monoethers, the equilibrium typically favors the alkyl- or arylmagnesium halide. Addition of dioxane to such solutions, however, leads to selective precipitation of dihalide MgX2(dioxane), driving the equilibrium completely to the right side of the equation. The dialkylmagnesium compounds are potent alkylating agents and are popular in the synthesis of organometallic compounds.
Chemical equilibrium
In a chemical reaction, chemical equilibrium is the state in which the concentrations of the reactants and products have not yet changed with time. It occurs only in reversible reactions, and not in irreversible reactions. Usually, this state results when the forward reaction proceeds at the same...
named after its discoverer Wilhelm Schlenk
Wilhelm Schlenk
Wilhelm Johann Schlenk was a German chemist. He was born in Munich and also studied chemistry there. Schlenk succeeded Hermann Emil Fischer at the University of Berlin in 1919....
taking place in solutions of Grignard reagents.
- 2 RMgX
MgX2 + MgR2
The process described is an equilibrium between two equivalents of an alkyl or aryl magnesium halide on the left of the equation and on the right side, one equivalent of the dialkyl or diaryl
Aryl
In the context of organic molecules, aryl refers to any functional group or substituent derived from an aromatic ring, be it phenyl, naphthyl, thienyl, indolyl, etc....
magnesium compound and magnesium halide 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...
. Organomagnesium halides in solution also form dimers and higher oligomer
Oligomer
In chemistry, an oligomer is a molecule that consists of a few monomer units , in contrast to a polymer that, at least in principle, consists of an unlimited number of monomers. Dimers, trimers, and tetramers are oligomers. Many oils are oligomeric, such as liquid paraffin...
s, especially at high concentration. Alkyl magnesium chlorides in ether are present as dimers.
The position of the equilibrium is influenced by solvent, temperature, and the nature of the various substituents. It is known that magnesium center in Grignard reagents typically coordinates two molecules of ether such as diethyl ether or tetrahydrofuran
Tetrahydrofuran
Tetrahydrofuran is a colorless, water-miscible organic liquid with low viscosity at standard temperature and pressure. This heterocyclic compound has the chemical formula 4O. As one of the most polar ethers with a wide liquid range, it is a useful solvent. Its main use, however, is as a precursor...
(THF). Thus they are more precisely described as having the formula RMgXL2 where L = an ether. In the presence of monoethers, the equilibrium typically favors the alkyl- or arylmagnesium halide. Addition of dioxane to such solutions, however, leads to selective precipitation of dihalide MgX2(dioxane), driving the equilibrium completely to the right side of the equation. The dialkylmagnesium compounds are potent alkylating agents and are popular in the synthesis of organometallic compounds.