Schlenk balance

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The Schlenk equilibrium describes the behavior of Grignard compounds (organic magnesium compounds) depending on the solvent . It was named after its discoverer Wilhelm Schlenk (1879–1943), who was one of the pioneers in the field of organometallic chemistry .

meaning

“The structure of the Grignard reagent, which has not yet been fully clarified, depends mainly on the concentration and solvent.” Solvents such as B. diethyl ether or tetrahydrofuran is used. Each carry two free electron pairs of these ether molecules are complex to the magnesium bound and provide the necessary stability octet from, what is the example of tetrahydrofuran, presented here in the literature as follows:

Grignard compound in solvent (tetrahydrofuran)

A closer look leads to a more detailed picture, the Schlenk equilibrium: In the production of an organic magnesium compound, different compounds are formed depending on the solvent used and depending on its capabilities in terms of coordination and solubility of the reaction products. The Schlenk equilibrium describes in a simple way which compounds occur in which solvent. The following figure describes the Schlenk equilibrium based on the literature. There is a balance between forms 1a and 1b . Depending on the solvent that stabilizes the Grignard compound in a complex , form 2a or 2b is formed.

Schlenk balance

At a low concentration of the solvent z. B. diethyl ether , the form 2a is preferred. Form 2a is also preferred for tetrahydrofuran as the solvent . Form 2b is fully formed in triethylamine . In the solvent 1,4-dioxane the insoluble magnesium halide precipitates and only dialkyl magnesium exists.

The Schlenk equilibrium was also observed at the Hauserbase [named after Charles R. Hauser (1900–1970)] with the empirical formula R 2 NMgCl. Hauser bases are Grignard analogs in which the alkyl radical R - has been replaced by an amide substituent R 2 N - .

Individual evidence

  1. ^ Wilhelm Schlenk , Wilhelm Schlenk jun.: About the constitution of the Grignard magnesium compounds . In: Reports of the German Chemical Society . tape 62 , no. 4 , April 3, 1929, pp. 920-924 , doi : 10.1002 / cber.19290620422 ( wiley.com ).
  2. ↑ a b Heinz GO Becker, Werner Berger, Günter Domschke, Egon Fanghänel, Jürgen Faust, Mechthild Fischer, Fritjof Gentz, Karl Gewald, Reiner Gluch, Roland Mayer, Klaus Müller, Dietrich Pavel, Hermann Schmidt, Karl Schollberg, Klaus Schwetlick, Erika Seiler, Günter Zeppenfeld: Organikum. Johann Ambrosius Barth Verlag, 1993, 19th edition, ISBN 3-335-00343-8 , pp. 563-572.
  3. ↑ Heinz GO Becker, Werner Berger, Günter Domschke, Egon Fanghänel , Jürgen Faust, Mechthild Fischer, Fritjof Gentz, Karl Gewald, Reiner Gluch, Roland Mayer , Klaus Müller, Dietrich Pavel, Hermann Schmidt, Karl Schollberg, Klaus Schwetlick, Erika Seiler, Günter Zeppenfeld: Organikum. Johann Ambrosius Barth Verlag, 1993, 19th edition, ISBN 3-335-00343-8 , p. 564.
  4. ^ Christoph Elschenbroich, Albrecht Salzer: Organometallics - A Concise Introduction . 2nd, rev. ed. Wiley-VCH, Weinheim 1995, ISBN 3-527-28164-9 , pp. 43-44 .
  5. ↑ Joachim Buddrus: Fundamentals of organic chemistry . 4th, revised and updated edition. De Gruyter, Berlin 2011, ISBN 978-3-11-024894-4 , pp. 445 .
  6. ↑ Neufeld, R .: DOSY External Calibration Curve Molecular Weight Determination as a Valuable Methodology in Characterizing Reactive Intermediates in Solution. In: eDiss, Georg-August-Universität Göttingen. 2016.