MHTCET 15 May 2024 Shift 1 Paper

Concept:Grignard reagents react with dry ice ($\mathrm{CO}_2$) to form carboxylic acids after acidic hydrolysis.Explanation:The given reagent is ethylmagnesium bromide, $\mathrm{CH}_3\mathrm{CH}_2\mathrm{MgBr}$.It reacts with dry ice, which is solid $\mathrm{CO}_2$, in dry ether.This forms the magnesium salt of propanoic acid.The reaction is:$$\mathrm{CH}_3\mathrm{CH}_2\mathrm{MgBr} + \mathrm{CO}_2 \xrightarrow{\text{dry ether}} \mathrm{CH}_3\mathrm{CH}_2\mathrm{COO}^-\mathrm{MgBr}^+$$On adding dilute hydrochloric acid, the salt is hydrolysed to give the carboxylic acid.$$\mathrm{CH}_3\mathrm{CH}_2\mathrm{COO}^-\mathrm{MgBr}^+ + \mathrm{HCl} \rightarrow \mathrm{CH}_3\mathrm{CH}_2\mathrm{COOH} + \mathrm{MgBrCl}$$The product is propanoic acid, $\mathrm{CH}_3\mathrm{CH}_2\mathrm{COOH}$.Answer:Propanoic acid, which is option B.