# Hydrolysis of Nitriles This document details the hydrolysis of nitriles, a significant organic reaction that converts nitriles into carboxylic acids or their salts using either dilute acid or dilute alkali. Nitriles are organic compounds containing the cyano group ($-C \equiv N$). The hydrolysis of nitriles involves the breaking of the carbon-nitrogen triple bond through reaction with water, typically under acidic or alkaline conditions. This method is particularly useful in organic synthesis because it allows for the extension of a carbon chain by one carbon atom (when starting from an alkyl halide). ## 1. Acid Hydrolysis of Nitriles When a nitrile is heated with a dilute acid, such as dilute hydrochloric acid ($HCl$) or dilute sulfuric acid ($H_2SO_4$), it undergoes hydrolysis to form a *carboxylic acid*. The acid acts as a catalyst and a reagent to protonate intermediates. - **Reagents:** Dilute acid (e.g., $HCl_{(aq)}$ or $H_2SO_{4(aq)}$) - **Conditions:** Heated - **Product:** Carboxylic acid **General Reaction:** $$ \mathrm{R-CN} + 2\mathrm{H}_2\mathrm{O} + \mathrm{H}^+ \xrightarrow{\text{heat}} \mathrm{R-COOH} + \mathrm{NH}_4^+ $$ During the reaction, an amide is formed as an intermediate, which then further hydrolyzes to the carboxylic acid. **Example: Hydrolysis of Ethanenitrile** $$ \mathrm{CH}_{3}\mathrm{CN}_{(\mathrm{aq})} + 2\mathrm{H}_2\mathrm{O}_{(\mathrm{l})} + \mathrm{HCl}_{(\mathrm{aq})} \longrightarrow \mathrm{CH}_3\mathrm{COOH}_{(\mathrm{aq})} + \mathrm{NH}_4\mathrm{Cl}_{(\mathrm{aq})} $$ - **Reactant:** Ethanenitrile ($CH_3CN$) - **Product:** Ethanoic acid ($CH_3COOH$) and ammonium chloride ($NH_4Cl$) ## 2. Alkaline Hydrolysis of Nitriles When a nitrile is heated with a dilute sodium hydroxide ($NaOH$) solution, an initial product, the *salt of a carboxylic acid*, is produced. This salt is then acidified with dilute hydrochloric acid ($HCl$) to yield the *free carboxylic acid*. This is a two-step process. - **Step 1: Reaction with alkali** - **Reagents:** Dilute sodium hydroxide solution ($NaOH_{(aq)}$) - **Conditions:** Heated - **Product:** Salt of carboxylic acid (e.g., sodium carboxylate) - **Step 2: Acidification** - **Reagents:** Dilute hydrochloric acid ($HCl_{(aq)}$) or another dilute acid - **Conditions:** Room temperature (usually) - **Product:** Free carboxylic acid **General Reaction Scheme:** **Step 1:** Formation of carboxylate salt $$ \mathrm{R-CN} + \mathrm{NaOH}_{(\mathrm{aq})}/\mathrm{H}_2\mathrm{O} \xrightarrow{\text{heat}} \mathrm{R-COONa}_{(\mathrm{aq})} + \mathrm{NH}_3 $$ *Note: Ammonia gas is typically evolved during this step.* **Step 2:** Acidification of carboxylate salt $$ \mathrm{R-COONa}_{(\mathrm{aq})} + \mathrm{H}^+_{(\mathrm{aq})} \longrightarrow \mathrm{R-COOH}_{(\mathrm{aq})} + \mathrm{Na}^+_{(\mathrm{aq})} $$ Or, using $HCl$: $$ \mathrm{R-COONa}_{(\mathrm{aq})} + \mathrm{HCl}_{(\mathrm{aq})} \longrightarrow \mathrm{R-COOH}_{(\mathrm{aq})} + \mathrm{NaCl}_{(\mathrm{aq})} $$