CO₂ + CH₃MgBr + H₂O Reaction and Mechanism

When CO₂ reacts with CH₃MgBr (methyl magnesium bromide) and water, CH₃COOH (ethanoic acid) is given as the product.

Carbon dioxide + Grignard reagent + water

Carbon dioxide reacts with a Grignard reagent compound and water and gives a carboxylic acid as the product. In this reaction, we can obtain a carboxylic acid compound increasing number of carbon atoms by one.

Carbon dioxide + Grignard reagent + water → carboxylic acid

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CO₂ + CH₃MgBr + H₂O = CH₃COOH + MgBr(OH)

Carbon dioxide, methyl magnesium bromide and water reaction

The complete reaction is mentioned above. But there is a sequence to add reagents to get the desired products. Otherwise reaction will not be succeeded as purposed.

CH₃MgBr exists in ether because we cannot store Grignard reagent in water or acidic medium or basic medium. Otherwise wee can say, ether is used as a solvent to keep CH₃MgBr stable. CH₃MgBr in ether medium exist as a solution.

How reactants are added?

1. Send CO₂ gas to CH₃MgBr / ether solution.
2. Then, add H₂O to the mixture.

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Mechanism of CO₂, CH₃MgBr and H₂O reaction

In carbon dioxide molecule, carbon atom has a small positive charge because oxygen atoms are much electronegative than carbon atom.

CH₃MgBr can be considered as a CH₃^- and ⁺MgBr because magnesium is a highly electropositive metal. Though CH₃^- can behave as a nucleophile.

First, CH₃^- attacks the positively charged carbon atom. Then bonds are configured to form new C-C bond.

When water is added to the mixture, a hydrogen atom is taken by -O^- and become a -OH group.

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Questions asked by students. Ask your question and find the answer free.

How do I use methanol to prepare ethanoic acid using methylmagnesium bromide ?

Indirectly you are asking that how to synthesis methyl bromide (bromomethane). This is a single step reaction. Reacting methanol and PBr₃ will give bromomethane (CH₃Br).

What are correct statements expressed about reaction of grignard reagent with CO₂

1. As the product, a secondary alcohol is given.
2. To get carboxylic acid as the final product, water should be added after the addition of grignard to carbon dioxide.
3. From this method, formic acid can be prepared by using correct grignard reagent.
4. In the presence of moisture with carbon dioxide, required product cannot be obtained.

2^nd and 4^th statements are correct.

Cannot use formaldehyde (HCHO) instead of CO₂ to prepare ethanoic acid?

HCHO reacts with CH₃MgBr and give Ethanol as the product. If CH₃COOH is required, ethanol has to be oxidized by a strong oxidizing agent.

Does require excess amount of CH₃MgBr to do the reaction such as some grignard reactions?

No, no need of excess CH3MgBr for this reaction because only one alkyl group is connected to the carbon dioxide molecule.

ch3cooh + ch3mgbr what will happen?

Grignard reagent will destroy and methane (CH₄) is produced as a organic product.

What will happen in this reaction? ch3mgbr + h2o

Remember that, grignard reagent hydrolysis when it meets water and an alkane compound is given as the product.

Can I use acidic water instead of water to recover the ethanoic acid in final step?

Yes. Acidic water can be used. It will also increase the reaction rate.

Can I prepare ethanol from CH₃MgBr + CO₂?

You have to go an extra step to produce ethanol from this reaction. When carbon dioxide reacts with methylmagnesium bromide and water, ethanoic acid is given. So you have to reduce ethanoic acid to ethanol by LiAlH₄.

What are the products of CH₃COOH + CH₃MgBr ?

Grignard reagent reacts with carboxylic acid and produce an alkane like below.

CH₃COOH + CH₃MgBr = CH₃COO^-+MgBr + CH₄

CH₃MgBr + CO₂, what will give?

a salt is given. To recover the carboxylic acid, you have to add water as a reagent at final statge.

CH₃MgBr + CO₂ = CH₃COO^-+MgBr

CH₃COO^-+MgBr + H₂O = CH₃COOH + MgBr(OH)

Are carboxylic acids given always grignard reagent with co2?

Yes. A carbon group is joint to carbon atom in the CO₂ molecule. Ethanoic acid is the simplest carboxylic acid can be prepared from this reaction. Remember that after mixing CO₂ and grignard reagent , water or acidic water should be added to the reaction mixture to get carboxylic acid.

Can benzoic acid be prepared from CO₂? If it possible, what are the reagent should I use?

Theoritically, it is possible. To react with CO₂, phenylmagnesium bromide or phenylmagnesium chloride should be used as the grignard reagent.

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