Amines

Question 1

Why are amines weak bases?

Answer 1

They can accept protons.

Their nitrogen atom has a lone pair of electrons meaning a dative covalent bond can be formed.

Question 2

Which amines are strongest and weakest bases?

Answer 2

Strongest
Primary aliphatic amines
Ammonia
Primary aromatic amine - phenylamine
Weakest

Primary/secondary/Tertiary amines have alkyl groups which push electrons towards the nitrogen.
Electron density at nitrogen increases so lone pair availability increases

Aromatic amines are less basic as the benzene group withdraws electron density from the Nitrogen atom.
Lone pair availability is reduced.

Question 3

Uses of quaternary ammonium ions?

Answer 3

Cationic surfactants

As they are positively charged they bind to negative ions forming quaternary ammonium salts.

They have a positive head group and a long hydrocarbon chain.

The hydrocarbon chain will bind to nonpolar substances like grease.
The cationic head will dissolve in water so they’re useful to remove grease as it allows them to mix.

Additionally, cationic surfactants have a positive ammonium ion which is attracted to negatively charged fibers meaning they will remove static.

Question 4

How to make aliphatic amines?

Answer 4

1. Heat halogenoalkane with excess ammonia (need 1:2) - nuc sub reaction.
   End up with a mixture of primary, secondary, tertiary and quaternary ammonium salts.
2. Reduce a nitrile to form a primary amine.

a) LiAlH4 reducing agent followed by dilute acid - this is too expensive in industrial use so instead:

b) Add Hydrogen gas with nickel catalyst at high temp and pressure
Catalytic hydrogenation

Question 5

How to make aromatic amines?

Answer 5

Reduce a nitro compound eg. nitro benzene.

Reflux tin + Conc HCl.
Then add NaOH

Question 6

What is an Amide?

Answer 6

A carboxylic acid derivative

-CONH2