Nitriles & Hydroxynitriles (Cambridge (CIE) A Level Chemistry): Flashcards

A nitrile is a compound containing the -CN functional group, prepared by nucleophilic substitution of a halogenoalkane with ethanolic KCN.

The halogenoalkane is heated under reflux with an ethanolic solution of potassium cyanide (KCN in ethanol). The CN^- ion acts as the nucleophile.

True.

The CN^- ion adds a carbon atom to the chain as it substitutes the halogen. This makes the reaction useful for chain extension in synthesis.

Hydroxynitriles contain both a -OH group and a -CN group, typically attached to the same carbon atom.

Step 1: The CN^- ion attacks the carbonyl carbon of ethanal, forming a negatively charged intermediate.

Step 2: The oxygen of the intermediate is protonated by H⁺ (from HCN, water or dilute acid) to give 2-hydroxypropanenitrile.

True.

Hydrolysis converts the -CN group into -COOH without adding or removing carbon atoms. The chain length is preserved, unlike nitrile formation which adds one carbon.

Nitriles can be hydrolysed by dilute acid to form a carboxylic acid and an ammonium salt, or by dilute alkali followed by acidification to form a carboxylic acid.

A hydroxynitrile is a compound with both -OH and -CN groups on the same carbon, formed by nucleophilic addition of HCN to an aldehyde or ketone.

Using aqueous KCN risks forming an alcohol (via hydrolysis) instead of the nitrile. Ethanolic KCN ensures the nucleophilic substitution proceeds to give the nitrile product.