Organomagnesium Compounds

Organomagnesium Compounds 

compounds that contain a carbon-magnesium bond. Two types of organomagnesium compounds are known: (1) complete compounds, such as magnesium dialkyls or magnesium diaryls, R₂Mg; and (2) mixed compounds, such as alkyl magnesium or aryl magnesium halides, RMgX (X = Cl, Br, I). Complete organomagnesium compounds are crystalline substances and are highly sensitive to the effects of oxygen, moisture, and carbon dioxide (they are self-igniting). Such compounds were first produced in the mid-19th century using the reaction of organomercuric compounds, R₂Hg, with magnesium; no use was found for them in organic synthesis.

In 1900 the French chemist F. Grignard developed a simple method of preparing mixed organomagnesium compounds and demonstrated a wide range of possible uses for them in organic synthesis. He established that metallic magnesium in absolute (anhydrous) ether reacts with alkyl or aryl halides, RX, to form compounds that pass into the ether solution. These compounds, known as Grignard reagents, are extremely unstable in free form. Therefore, they are not isolated but rather are used in the form of solutions, which are stable in the absence of moisture and atmospheric oxygen.

Subsequently, methods were developed for the preparation of Grignard reagents in hydrocarbon media (for example, benzene, xylene, and toluene) and in the absence of a solvent, which resulted in the possibility of using organomagnesium compounds in industry. However, the most widespread method has proved to be RMgX synthesis using ether solvents. An increase in the solvating properties of the solvent simplifies the formation of Grignard reagents. For example, vinyl halides, CH₂ = CHX, do not react with magnesium in ether but rather form organomagnesium compounds in tetrahydrofuran (H. Normant). Ethynyl magnesium halides may be produced by the interaction of alkyl magnesium halides and acetylene derivatives (Ž. Jocic):

C₆H₅C≡CH + C₂H₅MgBr - C₆H₅C≡CMgBr + C₂H₆

Organomagnesium compounds are widely used in the preparation of various types of organic compounds. The industrial synthesis of certain organosilicon compounds, aromatic substances, and Pharmaceuticals is carried out with the aid of organomagnesium compounds.

REFERENCE

Ioffe, F. T., and A. N. Nesmeianov. “Magnii, berilii, kal’tsii, strontsii, barii.” In the collection Metody elementoorganicheskoi khimii [part 1]. Edited by A. N. Nesmeianov and K. A. Kocheshkov. Moscow, 1963.

B. L. DIATKIN