Schlenk equilibrium

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.

The position of the equilibrium is influenced by solvent and temperature, the nature of the various substituents and the presence of impurities. It is known that magnesium atom in Grignard solutions, either RMgX, R2Mg or MgX2, can coordinate two molecules of ether (i.e. diethyl ether or tetrahydrofuran, THF). In the presence of ethereal solvent, the equilibrium tends to lie in favor of the alkyl or aryl magnesium halide. However, the addition of dioxane to an etheral Grignard precipitates out all of the magnesium halide species, driving the equilibrium completely to the right side of the equation.

Complexity is added to this equilibrium because the organomagnesium halide species in solution are capable of forming dimers and trimers etc. for instance when concentration is increased. Alkyl magnesium chlorides in ether are present as dimers.