Amines

Question 1

What are amines?

Answer 1

If one or more hydrogens in ammonia (NH3) is replaced with an organic group, you get an amine.

Question 2

Why are amines considered bases?

Answer 2

Amines will accept protons. There’s a lone pair of electrons on the nitrogen atom that forms a dative (coordinate) bond with an H+ ion.

Question 3

Amines + acids = ?

Answer 3

Amines are neutralised by acids to make an ammonium salt.

Question 4

How are aliphatic amines made?

Answer 4

By heating a haloalkane with an excess of ethanolic ammonia.You get a mixture of primary, secondary and tertiary amines and quaternary ammonium salts.Of which you can fractionally distil.

Question 5

How are aromatic amines made?

Answer 5

By reducing a nitro compound.Nitro compounds are reduced in two steps:1. Heat a mixture of nitro compound, tin metal and conc HCl under reflux- making a salt.2. Add sodium hydroxide.

Question 6

What are aromatic amines used to make?

Answer 6

Azo dyes

Question 7

What are azo dyes?

Answer 7

Man made dyes that contain the azo group, -N=N-.The azo group links two aromatic groups- creating a very stable molecule (the azo group becomes part of the delocalised electron system).

Question 8

What are the colours of azo dyes a result of?

Answer 8

Light absorption by the delocalised electron system.Different colours are made by combining different phenols and amines.

Question 9

Give some uses of azo dyes.

Answer 9

Food colouringsColours for clothingPaint pigmentsIndicators (methyl orange)

Question 10

State why some conditions must be kept at a low temperature.

Answer 10

Prevent decomposition

Question 11

Process of making an azo dye

Answer 11

1. Nitration- to get NO2 on 2. Reduction with tin and HCl (to swap NO2 for NH2)3. React the phenyl amine with nitrous acid and HCl

Question 12

Boiling point trend in amines

Answer 12

• Boiling points increase with molecular mass. • Amines have higher boiling points than corresponding alkanes because of intermolecular hydrogen bonding.

Question 13

Solubility of amines

Answer 13

• Soluble in organic solvents. • Lower mass compounds are soluble in water due to hydrogen bonding with the solvent. • Solubility decreases as molecules get heavier.

Question 14

Why are amines bases?

Answer 14

The lone pair on nitrogen makes amines basic. RNH2 + H+—> RNH3+

Question 15

Strength of bases in amines

Answer 15

• depends on the availability of the lone pair and thus its ability to pick up protons• the greater the electron density on the N, the better its ability to pick up protons• this is affected by the groups attached to the nitrogen.

Question 16

When 1-chloropropane is reacted with ethanolic ammonia what two amines may have been produced?How would this mixture be seperated?

Answer 16

Propylamine, dipropyl amineFractional distillation

Question 17

What are the equations for the usage of H2SO4 in nitration?

Answer 17

H2SO4 + HNO3 -> H2NO3+ + HSO4-H2NO3+ -> NO2+ + H2O (how NO2+ is produced).HSO4- + H+ -> H2SO4 (how its a catalyst that’s reformed).

Question 18

Equation for the production of an ammonium salt?

Answer 18

CH3CH2NH2 + HCl -> CH3CH2NH3+Cl-

Question 19

1. Making phenylamine conditions (nitrogenation)

Answer 19

50 degrees Conc H2SO4

Question 20

2. Reduction conditions

Answer 20

HCl Tin catalyst

Question 21

3. Diazotisation

Answer 21

React phenylamine with nitrous acid and HCl Less than 10 degrees

Question 22

4. Coupling

Answer 22

Couple the diazonium salt with a phenol that has been dissolved in NaOH solution (phenol is a coupling agent- it increases the electron density in the benzene ring.) Then chill in ice- azo dye precipitates out.