Grignard Reagents: A Blessing For Synthetic Chemists.

TCE

The Chemical Educator

ISSN: 1430-4171 (electronic version)

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Abstract Volume 8 Issue 6 (2003) pp 393-403

Grignard Reagents: A Blessing For Synthetic Chemists.

Saâd Moulay

Laboratoire de Chimie-Physique Moléculaire et Macromoléculaire, Département de Chimie Industrielle, Faculté des Sciences de L’Ingénieur, Université de Blida, Route de Soumaâ, B.P.270, Blida 09000, Algeria.
Received September 16, 2002. Accepted March 13, 2003.

Published online: 16 October 2003

Abstract. The intent of this manuscript is to bring to the undergraduate student (as well as the graduate one) at an early age as a chemist, an insight on the versatility and the peculiarity of the Grignard reagent. Grignard reagents are involved in various chemical reactions. Their synthesis calls for some precautions. The radical mechanism by which the Grignard reagent is formed is still enigmatic. RMgX is formed either on the magnesium surface according to the adsorption model of Walborsky or in solution according to the diffusion model of Garst. Also, the mechanism depends on the nature of R. For alkyl halides, the alkyl radical is the intermediate species, but the aryl radical is less probable for aryl halides. The Schlenk equilibrium shows the existence of three species: RMgX, R₂Mg, and MgX₂, which, altogether play a determining role in the reaction mechanism. RMgX exists either in monomeric or dimeric states depending on the solvent employed. The reagent’s powerfully nucleophilic character serves in reactions of many organic substrates, namely, carbonyl compounds. Interestingly, some of these reactions yield (quantitatively) some abnormal products arising from different mechanisms. The dual character of Grignard reagents, acting as Lewis acid and Lewis base, is valuable in the polymerization of some vinyl monomers. Also, each of the species of the Schlenk equilibrium is responsible for stereospecificity in the polymerization of some monomers to give either isotactic, syndiotactic, or stereoblock polymers. The wide applicability testifies to the preponderance of Grignard reagents over other reagents in chemical reactions.

Key Words: Of Special Interest; organic chemistry; Grignard reagents; Schlenk equilibrium; stereoregular PMMA

(*) Corresponding author. (E-mail: saadmoul@yahoo.com)

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