Properties of amines as bases

Question 1

How do amines react with acids?

Answer 1

to form salts

acts as a base

e.g.

ethylamine reacts with dilute hydrochloric acid

C₂H₅:NH₂ + H⁺ + Cl^- → C₂H₅NH₃⁺ + Cl^-

Question 2

Why does pheyl amine, an arylamine, insoluble but still will dissolve in excess hydrochloric acid?

Answer 2

because it forms the soluble ionic salt

Question 3

Why are amines considered to behave like bases?

Answer 3

they accept a proton

Question 4

WHat happens if a strong base like sodium hydroxide is added to the salt formed?

Answer 4

it removed the proton from the salt and regenerates the insoluble amine

Question 5

What does the strength of the base depend on?

Answer 5

how readily it will accept a proton

Question 6

Why do amines attract a proton?

Answer 6

due to the lone pair

Question 7

What is the inductive effect?

Answer 7

An inductive effect is an electronic effect due to the polarisation of σ bonds within a molecule or ion. This is typically due to an electronegatvity difference between the atoms at either end of the bond.

Question 8

What effect does the induictive effect have on the nitrogen atom in this case?

Answer 8

increases the electron density on the nitrogen atoms and therefore makes it a better electron pair donor

i,e. more attractive to protons

therefore primary alkylamines are stronger bases than ammonia

Question 9

What is the difference between base strength of primary, secondary and tertiary alkylamines?

Answer 9

secondary alkylamines have two inductive effect and are therefore stronger bases than 1º alkylamines

tertiary alkylamines are not stronger bases than secondary ones because they are less soluble in water

Question 10

Why are arylamines weak bases?

Answer 10

• aryl groups withdraw electrons form the nitrogen atom because the lone pair of electrons overlaps with delocalised system on the benzene ring
• lone pair on N
• delocalised / lone pair spread into ring
• less available to donate to H+