Ether diffusion

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In the chemical laboratory, ether diffusion is a technique used to produce crystals of sensitive compounds.

Ether diffusion is mostly used when crystals cannot be produced by simply evaporating the solvent , for example when the substance to be crystallized is sensitive to air or moisture. It is based on the fact that under reduced pressure a solvent (usually diethyl ether ), in which the compound is poorly soluble, slowly diffuses into the solution of the substance . The closer the pressure in the apparatus comes to the vapor pressure of the ether, the faster the diffusion takes place. The condition for this is that the ether is soluble in the other solvent. If not, the diffusion can also take place with other volatile substances, whereby the volatilityof the passing solvent must always be greater than that of the mother liquor .

method

The solution to be crystallized is placed in a Schlenk flask , usually a round-bottomed flask with a stopcock on the side, and, if necessary, connected to another Schlenk flask with diethyl ether with exclusion of air . A slight vacuum is then applied to the apparatus and the structure is left to stand. Fine crystals slowly separate out of the solution within a few days, and more than 1 ml of ether can easily pass over within an hour.