Nitriles and hydroxynitriles — practice questions

Step 1: Formation of butanenitrile from 1-bromopropane.

• Reagents: Potassium cyanide in ethanol (KCN in C₂H₅OH).
• Conditions: Heat under reflux.
• Reaction Type: Nucleophilic substitution.
• Equation: $\text{CH}_3\text{CH}_2\text{CH}_2\text{Br} + \text{KCN} \rightarrow \text{CH}_3\text{CH}_2\text{CH}_2\text{CN} + \text{KBr}$

Step 2: Hydrolysis of butanenitrile to butanoic acid.

• Reagents: Dilute sulfuric acid (H₂SO₄(aq)) or dilute hydrochloric acid (HCl(aq)).
• Conditions: Heat under reflux.
• Reaction Type: Acid hydrolysis.
• Equation: $\text{CH}_3\text{CH}_2\text{CH}_2\text{CN} + 2\text{H}_2\text{O} + \text{H}^+ \rightarrow \text{CH}_3\text{CH}_2\text{CH}_2\text{COOH} + \text{NH}_4^+$

Product Name: 2-hydroxypropanenitrile.

Mechanism: Nucleophilic Addition

Step 1: The nucleophilic cyanide ion attacks the electron-deficient carbonyl carbon atom of ethanal. The π-bond in the C=O group breaks, and the pair of electrons moves onto the oxygen atom.

Diagrammatic representation: Arrow from the lone pair on the carbon of :C≡N⁻ to the C of the C=O group. A second arrow from the C=O double bond to the O atom.

$\text{CH}_3\text{CHO} + :\text{CN}^- \rightarrow [\text{CH}_3\text{CH(CN)O}]^-$ (intermediate)

Step 2: The negatively charged oxygen atom of the intermediate is a strong base and is protonated by a hydrogen ion (from HCN or the acid catalyst) to form the hydroxyl group.

Diagrammatic representation: Arrow from a lone pair on the O⁻ of the intermediate to an H⁺ ion.

$[\text{CH}_3\text{CH(CN)O}]^- + \text{H}^+ \rightarrow \text{CH}_3\text{CH(OH)CN}$