28.2 The properties of amines as bases

Question 1

Why are amines bronsted lowry bases

Eg soluble amines

Answer 1

Amines can accept a proton

Eg the lone pair on nitrogen can accept one from HCl

Eg phenylamine is soluble will bond with the hydrogen from HCl to make phenylammonium chloride

The products will evaporate however

Question 2

What is formed when insoluble amines react with acids

How is the amine regenerated

Answer 2

Salts are formed

Eg ethylamine reacts with HCl to make ethylammonium chloride

If you add NaOH or any strong base, it removes the proton from the salt and regenerates the insoluble amine

Question 3

What does the strength of a base depend on

Answer 3

It depends on how readily it can accept a proton H+.

Both ammonia and amines have a lone pair of electrons that attract a proton

The presence of alkyl groups can influence

Question 4

How does the positive inductive effect influence how amines act as bases

Answer 4

. Alkyl groups release electrons away from the alkyl group and towards the nitrogen atom

. This means the lone pair on nitrogen is more electron dense so can donate a pair of electrons to get a H+ added

Question 5

What is the strongest type of amine base,
give the order of strength

Answer 5

Secondary amines are the strongest bases as there are two tertiary groups so two inductive effects.

They are stronger than tertiary because they are more soluble in water.

Then it is tertiary, primary, ammonia and then finally phenylamine

Question 6

Why is phenylamine the weakest base

Answer 6

. Aryl group (eg benzene) can withdraw electrons from the nitrogen atom because the lone pair overlaps with the delocalised system on the benzene ring

. This means the nitrogen is less electron dense so is a worse electron donor