Question

Treating a Grignard reagent with carbon dioxide followed by aqueous HCl gives a carboxylic acid.

Short answer

Question: Explain the process of forming a carboxylic acid using a Grignard reagent, carbon dioxide, and aqueous HCl. Answer: The formation of a carboxylic acid using a Grignard reagent involves three main steps. First, a Grignard reagent is formed by reacting an alkyl or aryl halide with magnesium metal in an ether solvent. Second, the Grignard reagent reacts with carbon dioxide in a nucleophilic addition reaction to form a magnesium salt of the carboxylic acid. Finally, the magnesium salt is hydrolyzed using aqueous HCl, which replaces the magnesium halide with a hydrogen atom, ultimately yielding a carboxylic acid.

Step-by-step solution

Formation of Grignard Reagent

The first step in the reaction is the formation of a Grignard reagent. Grignard reagents have the general formula RMgX, where R is an alkyl or aryl group and X is a halogen (usually Cl, Br, or I). They are formed by the reaction of an alkyl or aryl halide with magnesium metal in an ether solvent. R-X + Mg → R-Mg-X

Reaction with Carbon Dioxide

The Grignard reagent reacts with carbon dioxide in a nucleophilic addition reaction to form a magnesium salt of the carboxylic acid. Carbon dioxide, as an electrophile, reacts with Grignard reagent, which acts as a nucleophile. R-Mg-X + CO2 → R-CO2Mg-X

Hydrolysis with Aqueous HCl

The final step is to make the carboxylic acid by hydrolyzing the magnesium salt with aqueous HCl. The hydrolysis replaces the magnesium halide with a hydrogen atom, yielding a carboxylic acid. R-CO2Mg-X + HCl → R-COOH + MgXCl Overall, the reaction converts an alkyl or aryl halide into a carboxylic acid by first forming a Grignard reagent, then reacting it with carbon dioxide, and finally hydrolyzing the magnesium salt with aqueous HCl.