3.11 amines

what is a primary amine

1 carbon atom bonded to nitrogen atom

represented as RNH₂

what is a secondary amine

two carbon atoms bonded to the nitrogen atom

represented as R₂NH

what is a tertiary amine

three carbon atoms bonded to the nitrogen atom

represented as R₃N

what property do aliphatic amines have

act as bases as the lone pair of electrons on nitrogen is readily available for forming a dative covalent bond with a H⁺ so accepting a proton

why are primary aliphatic amines stronger bases than ammonia

the alkyl groups are electron releasing and push electrons towards the nitrogen atom making the lone pair of electrons on the nitrogen more readily available to accept protons

why are secondary amines stringer than primary amines

more alkyl groups

more electron density is pushed onto the N atom, making the lone pair of electrons more readily available

base strength of primary aromatic amines

lone pair of electrons on nitrogen delocalise with the ring of electrons in the benzene ring

lone pair on N is less able to accept protons

overall order of base strength

aromatic amines < ammonia < primary amines < tertiary amines < secondary amines

when amines react with acids what do they form

ammonium salts

are the ionic salts formed soluble

yes in acid

what does the addition of NaOH to an ammonium salt do

convert it back to the amine

how do you make a basic buffer

combine a weak base with a salt of that weak base

e.g. ammonia and ammonium chloride

methylamine and methylammonium chloride

reaction of halogenoalkanes with ammonia forming a primary amine

reaction of halogenoalkanes with ammonia forming a secondary amine

reaction of halogenoalkanes with ammonia forming a tertiary amine

reaction of halogenoalkanes with ammonia forming a quaternary ammonium salt

what does using an excess of ammonia promote

formation of primary amine

what does using an excess of the halogenoalkane promote

formation of the quaternary salt

use of quaternary salts

cationic surfactants

reduces tension of liquids

preparing amines from nitriles in a 2 step reaction

1. convert halogenoalkane to nitrile

2. reduce nitrile to amine

halogenoalkane to nitrile

using KCN in aqueous ethanol

heat under reflux

CH₃CH₂Br + CN^- ——> CH₃CH₂CN + Br^-

nitrile to amine

using LiAlH₄ in ether

or reducing with H₂ using a Ni catalyst

CH₃CH₂CN + 4[H] —→ CH₂CH₂CH₂NH₂

disadvantage of two step reaction

low yield