amines

primary amines

have 1 alkyl group attached

secondary amines

have 2 alkyl groups attached

tertiary amines

have 3 alkyl groups attached

how primary amines can be formed

• by nucleophilic substitution between halogenoalkanes and ammonia

• need excess ammonia

reaction mechanism between bromoethane and ammonia

• forms primary amine

reaction mechanism between bromoethane and ethylamine

• forms secondary amine

reaction mechanism between bromoethane and diethylamine

• forms tertiary amine

reaction mechanism between bromoethane and triethylamine

• forms quaternary ammonium salt

what are quaternary salts used as?

• cationic surfactants

• e.g. in hair conditioner and fabric softners

preparing amines from nitriles

1. convert halogenoalkane to nitrile using KCN in aqueous ethanol and heat under reflux

   • CH₃CH₂Br + CN⁻ ———> CH₃CH₂CN + Br⁻

2. reduce nitrile to amine using LiALH₄ in ether

   • CH₃CH₂CN + 4[H] ———> CH₃CH₂CH₂NH₂

disadvantage of preparing amines from nitriles

• two step reaction, therefore low yield

• KCN is toxic

Explain why nucleophilic substitution produces a less pure product than reduction

further substitution reactions occur and other products formed

• whereas reduction only forms one product

reducing nitroarenes to aromatic/phenyl amines

• reagent: tin catalyst and conc. HCl

• conditions: heat under reflux

reaction of acyl chloride with primary amine

• change in functional group: acyl chloride to secondary amide

• reagent: primary amine

• conditions: room temp.

• observation: nvc

reaction mechanism of ethanoyl chloride with ethylamine

reaction of acid anhydride with primary amine

• change in functional group: acid anhydride to secondary amide

• reagent: primary amine

• conditions: room temp.

• observations: nvc

reaction equation of ethanoic anhydride and methylamine

explain why aliphatic amines are stronger bases than ammonia

• the alkyl groups are electron releasing and they push electrons towards N atom

• inductive effect pushes electrons

• positive inductive effect

• therefore making lone pair of electrons on N atom more readily available to accept protons

explain why secondary amines are stronger bases than primary amines

• secondary amines have more alkyl groups that are substituted onto the N

• so more electron density is pushed onto the N atom

  • since the inductive effect of alkyl groups is greater than H atoms

  • positive inductive effect

• therefore making the l.p of electrons on the N atom more readily available

overall order of base strength

strongest

1. secondary amines

2. primary amines

3. ammonia

4. aromatic amines

weakest

explain the base strength of aromatic amines

• aromatic amines do not form basic solutions

• this is bc the l.p of electrons on the N delocalise with the ring of electrons in the benzene

• this means that the l.p on the N atom is less able to accept p+