Nitrogen Compounds: Amines and Nitriles

This guide covers subtopics 19.1, Primary amines, and 19.2, Nitriles and hydroxynitriles, from Topic 19 of Cambridge International AS & A Level Chemistry 9701, 2025–2027 series. Both are AS Level content, combined here because 19.1 is a single-outcome subtopic and much of 19.2 is really a cross-reference to reactions already established elsewhere — this resource is best read as making those connections explicit, rather than as introducing a large body of new reaction content.

Before studying this

This resource assumes Halogenoalkanes: Nucleophilic Substitution and Elimination (both amines and nitriles are made from a halogenoalkane) and Carbonyl Compounds: Aldehydes and Ketones (hydroxynitriles are the product already covered there). Classification of amines (primary/secondary/tertiary) is explicitly not tested at AS Level — if you’ve seen it in a general chemistry context, set it aside for this syllabus point.

Syllabus coverage

CAMBRIDGE INTERNATIONAL AS & A LEVEL CHEMISTRY 9701 — AS Level, Topic 19

19.1 Primary amines — recalling the reaction by which amines are produced: a halogenoalkane with NH₃ in ethanol, heated under pressure. Classification of amines is not tested at AS Level.

19.2 Nitriles and hydroxynitriles — recalling the reaction by which nitriles are produced (a halogenoalkane with KCN in ethanol and heat); recalling the reaction by which hydroxynitriles are produced (an aldehyde or ketone with HCN, KCN as catalyst, and heat); describing the hydrolysis of nitriles with dilute acid or dilute alkali followed by acidification, to produce a carboxylic acid.

Primary amines

A primary amine has the general structure R–NH₂. The only production route required at AS is:

R–X + 2NH₃ → R–NH₂ + NH₄X

carried out with the halogenoalkane in ethanol, heated under pressure (a sealed vessel — ammonia would otherwise escape as a gas). An excess of ammonia is used in practice, though the reasoning behind that (avoiding further substitution at the newly-formed amine) belongs to the classification ideas this syllabus point explicitly excludes at AS — you’re only required to know the reaction itself, for example:

CH₃CH₂Br + 2NH₃ → CH₃CH₂NH₂ + NH₄Br

This is the same nucleophilic substitution framework as the other reactions of halogenoalkanes in Halogenoalkanes: Nucleophilic Substitution and Elimination — ammonia acts as the nucleophile here, in the same way hydroxide, cyanide and water do elsewhere in that resource.

Nitriles

A nitrile has the general structure R–C≡N. Its production route is the cyanide-ion equivalent of the amine reaction above:

R–X + KCN → R–CN + KX

carried out in ethanol, with heat. This is the same reaction already listed among the nucleophilic substitution reactions of halogenoalkanes — CN⁻ attacking the halogenoalkane’s electrophilic carbon exactly as OH⁻ does when producing an alcohol.

Hydrolysis of a nitrile — with dilute acid or dilute alkali, followed by acidification — produces a carboxylic acid:

R–CN + 2H₂O + H⁺ → R–COOH + NH₄⁺

This is one of the three production routes to a carboxylic acid listed in Carboxylic Acids and Esters.

Hydroxynitriles

A hydroxynitrile is produced by the nucleophilic addition of HCN to an aldehyde or ketone — covered in full, mechanism included, in Carbonyl Compounds: Aldehydes and Ketones.

The same nucleophile, two different mechanisms

It’s worth noticing directly: cyanide, CN⁻, is the nucleophile in both the nitrile and the hydroxynitrile reactions above — but the mechanism is different in each case, because the carbon being attacked is different:

• Attacking a halogenoalkane’s sp³ carbon (bonded to a leaving group, the halogen) is nucleophilic substitution — the halide ion leaves as CN⁻ arrives.
• Attacking a carbonyl compound’s sp² carbon (double-bonded to oxygen, no leaving group) is nucleophilic addition — nothing leaves; the π bond breaks instead, and the oxygen becomes an alkoxide that’s subsequently protonated.

Recognising which substrate you’re looking at — a C–X bond, or a C=O bond — tells you immediately which mechanism type is expected in an answer.

Worked example. A synthetic route converts bromoethane into 2-hydroxypropanenitrile in three steps. Suggest the steps and reagents.

Bromoethane, CH₃CH₂Br, must first become a carbonyl compound before HCN can add to it. Step 1: hydrolyse the halogenoalkane with NaOH(aq), heat, to give ethanol, CH₃CH₂OH. Step 2: oxidise the ethanol with acidified K₂Cr₂O₇ and distil, to give ethanal, CH₃CHO. Step 3: react the ethanal with HCN (KCN catalyst, heat) to give the hydroxynitrile, CH₃CH(OH)CN. (Three steps are needed, not two, since a halogenoalkane cannot be converted directly to a carbonyl compound — this is a useful reminder that synthetic routes often need more steps than first expected.)

Common mistakes

• Trying to classify an amine as primary, secondary or tertiary for exam purposes. The syllabus explicitly excludes this at AS — focus on the one required production reaction.
• Confusing the nitrile and hydroxynitrile production reactions. Both use a cyanide source, but the nitrile comes from a halogenoalkane (substitution) while the hydroxynitrile comes from a carbonyl compound (addition) — different substrates, different mechanisms, different products.
• Forgetting nitrile hydrolysis needs a final acidification step when dilute alkali is used, since the initial product under alkaline conditions is the carboxylate salt, not the free carboxylic acid — the same acid/alkali distinction as ester hydrolysis.
• Assuming any nucleophile always reacts by the same mechanism. Mechanism type depends on the substrate (is there a leaving group, or a π bond to add across?), not on which nucleophile is being used.

Quick revision checklist

• Primary amine production: halogenoalkane + NH₃ (ethanol, heat, pressure) — classification not required at AS
• Nitrile production: halogenoalkane + KCN (ethanol, heat) — nucleophilic substitution
• Hydroxynitrile production: carbonyl compound + HCN (KCN catalyst, heat) — nucleophilic addition
• Nitrile hydrolysis (dilute acid or alkali, then acidify) → carboxylic acid
• Why the same nucleophile (CN⁻) gives substitution with one substrate and addition with another

Related resources

• Halogenoalkanes: Nucleophilic Substitution and Elimination — the substitution reactions amines and nitriles both come from
• Carbonyl Compounds: Aldehydes and Ketones — the nucleophilic addition mechanism, in full
• Carboxylic Acids and Esters — where nitrile hydrolysis leads
• Amines: Aliphatic and Aromatic, Basicity and Azo Dyes — the A Level continuation, adding secondary amines and phenylamine
• Cambridge AS & A Level Chemistry hub

Written against Cambridge International AS & A Level Chemistry 9701, 2025–2027 series. Always check the current syllabus for your examination year.