MCQ Detailed View

Grignard reagents are one of the most important tools in organic synthesis. They are represented as R–MgX, where R is an alkyl or aryl group and X is a halogen such as chlorine, bromine, or iodine. Ethyl magnesium iodide (C₂H₅MgI) is a typical Grignard reagent prepared by reacting ethyl iodide with magnesium metal in dry ether. These reagents are highly reactive toward electrophiles.

When carbon dioxide (CO₂) is introduced to ethyl magnesium iodide, the nucleophilic carbon in the ethyl group attacks the electrophilic carbon of CO₂. This leads to the formation of a magnesium carboxylate salt. The intermediate formed is C₂H₅COO⁻Mg⁺I.

In the next step, the reaction mixture is treated with dilute acid, usually HCl or H₂SO₄. Acid hydrolysis protonates the carboxylate anion, converting it into a free carboxylic acid. The final product obtained is propanoic acid (C₂H₅COOH).

This reaction is very useful because it extends the carbon chain by one carbon atom. Here, the two-carbon ethyl group becomes part of a three-carbon carboxylic acid. This method is widely used in laboratories for the synthesis of higher carboxylic acids.

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  Propane is not possible since no hydrogenation takes place.

  
  


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  Propanal would result from the reaction of a Grignard reagent with formaldehyde.

  
  


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  Propanol is formed when a Grignard reagent reacts with aldehydes or ketones, not CO₂.

  
  

Thus, only propanoic acid is the correct product of this carboxylation reaction.