A-level Chemistry: 3.3.11 Amines

Lone pair of electrons on nitrogen atom in tertiary amine can also bond with 4th organic group

Quaternary ammonium ions are positively charged ∴ form bonds around with -ve ions & form complexes (quaternary ammonium salts)

Quaternary ammonium salts with at least 1 long hydrocarbon chain

Fabric cleaners (e.g. fabric conditioner) and hair products (e.g. conditioner)

• Hydrocarbon tail binds to non-polar substances like grease & cationic head dissolves in water

• Positively charged part (ammonium ion) will bind to negatively charged surfaces e.g. hair and fibre
  

  • Gets rid of static

∵ accept protons

Lone pair of electrons on nitrogen atom can form dative covalent (coordinate) bond with H+ ion

Depends on how available nitrogen’s lone pair of electrons is

More available the lone pair is = more likely amine is to accept proton & stronger base it’ll be

When its electron density is high

1. Aromatic amines (weakest)

2. Ammonia

3. Aliphatic amines (strongest)

• Benzene ring draws electrons towards itself and nitrogen lone pair gets partially delocalised onto the ring

• ∴ the electron density on nitrogen ↓, making lone pair much less available

• Alkyl groups push electrons onto attached groups

• ∴ electron density on nitrogen atom ↑

• Makes lone pair more available

∵ have lone pair of electrons

• React with halogenoalkanes in nucleophilic substitution

• React with acyl chlorides and acid anhydrides in nucleophilic addition-elimination

1. Heating halogenoalkane with excess ammonia

2. Reducing a nitrile (to a primary amine)

Mixture of primary, secondary, tertiary amines + quaternary ammonium salts

1. Primary amine 1st produced has lone pair of electrons = nucleophile

2. ∴ can react with any remaining halogenoalkane in nucleophilic substitution reaction

3. Further substitutions take place as long as there’s remaining halogenoalkane

4. Happens up to quaternary ammonium salt = can’t react further ∵ has no lone pair

Mechanism is similar to reaction of ammonia + halogenoalkane: 2 amine molecules react with halogenoalkane in succession to form more substituted amine (e.g. primary amine forms secondary amine) & ammonium salt with similar structure to original amine

1. Use lithium aluminium hydride (LiAlH4 - strong reducing agent) in non-aqueous solvent e.g. dry ether followed by dilute acid

2. Catalytic hydrogenation: Reduced using hydrogen gas with metal catalyst e.g. platinum or nickel at high temperature and pressure

LiAlH4 is too expensive

| (industry uses catalytic hydrogenation)

Reduce nitro compound e.g. nitrobenzene

1. Heat mixture of nitro compound, tin metal & concentrated HCl under reflux

   • Makes salt

   • e.g. using nitrobenzene, salt formed = C6H5NH3+Cl-

2. To turn salt into aromatic amine, add alkali e.g. NaOH solution

Are starting molecules for lots of dyes and pharmaceuticals

Amides are carboxylic acid derivates

-CONH2

Carbonyl group pulls electrons away from NH2 group

Ability of alkyl group to release electrons towards nitrogen atom

CH3CH2NH3Cl

• (weak base + salt = alkaline buffer solution)

• (ethylamine + amine hydrochloride = alkaline buffer solution)

  • (add HCl to ethylamine to get salt)

N-ethylpropanamide

CH3CH2CH2NH2 + H+ → CH3CH2CH2NH3+

(original equation: CH3CH2CH2NH2 + HCl → CH3CH2CH2NH3Cl)