Grignard Reagent - Structure, Preparation, Application, Uses, FAQs

Grignard compound or Grignard reagent is a chemical compound and the general formula of Grignard reagent is RMgX. And X is any halogen compounds that are Cl, F, Br, and I and R is an organic group that may be alkyl or aryl group. One of the very common examples of Grignard reagent is methyl magnesium chloride that is Cl-Mg-CH₃. These compounds can also be called organomagnesium compounds subclass.

For the preparation of the Grignard reagent, a magnesium ribbon is used and the magnesium is covered with a passivating film of magnesium oxide that can be used in order to prevent the reaction with the organic halide. These compounds are similar to organolithium reagents that can be used for many organic synthesis reactions for the formation of new carbon-carbon bonds. When Grignard reagents react with alkyl halides in the presence of a suitable catalyst and a new compound that is R-R’ is formed as the product.

Grignard reagents are highly reactive solid compounds so they are handled as solutions in solvents with diethyl ether or tetrahydrofuran. The French chemist Victor Grignard won the Nobel prize for the discovery of Grignard reagent in 1912. To find the number of halogen atoms in halogen compounds Grignard reagents can be used. The degradation reaction of the Grignard reagent is used for the chemical analysis of triacylglycerol and also for some cross-coupling reactions that are involved in the formation of the carbon-carbon bond.

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Structure of Grignard reagent

Preparation of Grignard reagent

Grignard reagents are prepared from magnesium metal by treating with an organic halide. For stabilizing these organomagnesium compounds ethers are required. These compounds require air-free conditions and the use of protic solvent may not be used as it will create protonolysis or oxidation may destroy these compounds.

But this compound can be formed in solution by the use of ultrasound since they activate the magnesium thereby they consume water present in the solution. For the preparation of the Grignard reagent, an anhydrous condition is more suitable. By following correct procedures result in the formation of the Grignard reagent. The following figure shows the preparation of Grignard regent from an organic halide.

Reaction with carbonyl compounds

Grignard reagents react with carbonyl compounds like ketone and aldehydes to form corresponding alcohols. The nature of the substituent that gets attached to the carbonyl compound determines the product. When methanal is used as an aldehyde the obtained alcohol will be primary and if any aldehyde other than this is used a secondary aldehyde is obtained. It can also be used for the alkylation of aldehydes and ketones. Grignard reagent acts as a nucleophile and thereby nucleophilic substitution reactions are taking place. The below figure shows the reaction of the Grignard reagent to form Benzyl alcohol.

Reaction of Grignard reagent with water-

The reaction of a carbonyl compound with the Grignard reagent.

Reactions acting as a base

Grignard reagents are basic compounds and they react with phenols alcohols acceptor to give their corresponding alkoxides that is ROMgBr.

Grignard agents can be used for the alkylation of metals

Grignard reagents react with the metal to form their related compound. For example, when Grignard reagent reacts with cadmium chloride it forms a di alkyl cadmium by the transmethylation reaction. The following reaction explains this.

2RMgX+CdCl₂R₂Cd+2MgXCl

Schlenk equilibrium

Grignard reagent reaction with dioxane to give di organomagnesium compounds and the reaction involving is known as Schlenk equilibrium. And the reaction is conducted in a solvent that is diethyl ether and tetrahydrofuran.

2RMgX+dioxane→R₂Mg+MgX₂

Oxidation

Grignard reagent reaction with oxygen and forms magnesium organic peroxide. And they further hydrolysis of the compound obtained hydroperoxides or alcohol. The following reaction shows the formation of this and it proceeds in radical intermediates.

Also Read:

• NCERT solutions for Class 12 Chemistry Chapter 10 Haloalkanes and Haloarenes
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Uses of Grignard reagent

• Grignard reagents are a very important organic compound that has many applications in the chemical field mainly the organic chemistry field.
• Grignard reagents have industrial applications also. The very important use of the Grignard reagent is the production of tamoxifen a medicine used for the treatment of breast cancer. The below reaction shows the preparation of tamoxifen.

Preparation of tamoxifen

• Grignard reagents can be used to produce alcohol from epoxides.
• Grignard reagent reaction with aldehyde ketone and esters to form alcoholic compounds.
• It can be used for the degradation reaction of Grignard reagent is used for the chemical analysis of triacylglycerol and also for some cross-coupling reactions that are involved in the formation of carbon-carbon and carbon atom bonds.
• It can be used for the synthesis of many organometallic compounds.
• Grignard reagents are best for the preparation of amides, acetals, amino compounds, organosulphur compounds, ethers, ketones, aldehydes, etc.
• It can be used for the production of several compounds that has a very important application in the pharmaceutical, perfume, and specialty chemicals field.
• Grignard reagents are used for the production of optically active compounds by the reaction of secondary alcohol with the alkyl halides in presence of a chiral phosphine metal as a catalyst.

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NCERT Chemistry Notes:

• NCERT Notes Class 11th Chemistry
• NCERT Notes Class 12th Chemistry
• NCERT Notes For All Subjects