Amines

Question 1

How do you classify amines as primary, secondary and tertiary?

Answer 1

If there is one alkyl group attached to the nitrogen, it is primary
If there are two alkyl groups attached to the nitrogen, it is secondary
If there are three alkyl groups attached to the nitrogen, it is tertiary

Question 2

What are quaternary amines?

Answer 2

Where the nitrogen has four alkyl groups attached. These will form ammonium cations, which are positively charged

Question 3

What are the two main ways of making primary aliphatic amines?

Answer 3

Starting from halogenoalkanes or nitriles

Question 4

What is equations for the formation of a primary amine from a halogenoalkane?

Answer 4

Halogenoalkane + NH3 -> Primary amine + HX

Question 5

What conditions must be used for the formation of primary amines from halogenoalkanes?

Answer 5

For gaseous ammonia, the mixture must be heated in a sealed container
Alternatively, the halogenoalkane can be mixed with conc aqueous ammonia.
Ammonia should be in excess

Question 6

Why should ammonia be in excess when forming amines from halogenoalkanes?

Answer 6

The amine formed has a nitrogen containing a lone pair of electrons, which means it could act as a nucleophile, competing with ammonia for the attack on the halogenoalkane, which will form a secondary amine.
To minimise the chance of secondary amines from being formed, ammonia is used in excess, so it outcompetes the primary amine as a nucleophile

Question 7

What does some of the excess ammonia react with to form?

Answer 7

Some excess ammonia will react with produced HCl to form an ammonium chloride salt.
So a better equation would be:
Halogenoalkane + 2NH3 -> Primary amine + NH4Cl

Question 8

Through what process can primary amines be produced from nitriles?

Answer 8

Nitriles can be reduced to primary amines

Question 9

What is the reducing agent for the reduction of nitriles to primary amines?

Answer 9

Lithium tetrahydridoaluminate

Question 10

What is the equation for the reduction of ethanenitrile to ethyl amine?

Answer 10

CH3CN + 4[H] -> CH3CH2NH2

Question 11

For the reduction of nitriles to primary amines, what is the solvent and why?

Answer 11

The solvent is dry ether, to ensure that there is no water that could affect the reaction

Question 12

What is reduced to form aromatic amines?

Answer 12

Nitrobenzene

Question 13

What is the formula for nitrobenzene?

Answer 13

C6H5NO2

Question 14

What is the reducing agent and conditions used for the reduction of nitrobenzene to an aromatic nitrile?

Answer 14

The reducing agent is tin mixed with concentrated HCl, and it is heated under reflux

Question 15

What is product of the the reduction of C6H5NO2?

Answer 15

Phenyl amine (C6H5NH2)

Question 16

What is the equation for the reduction of nitrobenzene to phenylamine?

Answer 16

C6H5NO2 + 6[H] -> C6H5NH2 + 2H2O

Question 17

What will phenylamine form due to the acidic conditions, and how is this overcome?

Answer 17

Phenylamine is basic so will react with the acid present to form the phenylammonium ion. However this can easily be converted back to phenylamine with the addition of an alkali (e.g. NaOH)

Question 18

What is the equation for the conversion of phenylammonium back to phenylamine?

Answer 18

OH- + C6H5NH3+ -> C6H5NH2 + H2O

Question 19

Why are (some shorter chain) amines soluble in water?

Answer 19

Hydrogen bonds form between the hydrogens attached to the nitrogen in the amine and the oxygen in water

Question 20

How do amines react with water (use methylamine as the example)?

Answer 20

CH3NH2 + H2O <=> CH3NH3+ + OH-

Question 21

What are the amines acting as when reacting with water?

Answer 21

As a base (as they are attracting/receiving a proton)

Question 22

How does the basicity of ammonia compare to methylamine and why?

Answer 22

Methylamine is a stronger base than ammonia, as the methyl group is electron-releasing, and so the nitrogen has an increased electron density (so can more easily receive protons)

Question 23

How does the basicity of aliphatic amines change as chain length increases?

Answer 23

The basicity increases, but only slightly, as the ethyl and propyl groups are only slightly more electron-releasing than the methyl group

Question 24

How does the basicity of aromatic amines compare to aliphatic amines and why?

Answer 24

Aromatic amines, like phenylamine, have a much lower basicity than aliphatic amines.
This is because the lone pair of electrons on the nitrogen are displaced towards the pi bond of the electron ring; this makes the nitrogen less electron rich and the lone pairs less available

Question 25

How do amines react with strong acids?

Answer 25

All amines react with strong acids to form ionic salts. | e.g CH3NH2 + HCl -> CH3NH3+Cl-

Question 26

What type of mechanism is the reaction between ethanoyl chloride and amines and why?

Answer 26

The reaction is addition-elimination, as one molecule is added to another, and in this joining a small molecule is eliminated (in this case HCl)

Question 27

What do amines and ethanoyl chloride react to form?

Answer 27

Amides and HCl

Question 28

What is the functional group of amides?

Answer 28

O=C-NR2

Question 29

Why do halogenoalkanes and amines react?

Answer 29

The electron-deficient carbon of the halogenoalkane is attacked by the electron-rich nitrogen of the amine

Question 30

How are secondary amines formed using halogenoalkanes?

Answer 30

Primary amines react with halogenoalkanes to form secondary amines and HX

Question 31

How are tertiary amines formed using halogenoalkanes?

Answer 31

Secondary amines react with halogenoalkanes to form tertiary amines and HX

Question 32

How are quaternary amines formed using halogenoalkanes?

Answer 32

Tertiary amines react with halogenoalkanes to form quaternary amines and X-

Question 33

Why is HX not formed in the formation of quaternary amines used halogenoalkanes?

Answer 33

Because there is no hydrogen to lose from the amine group, as they have all already been replaced by alkyl groups. Instead the product is a quaternary ammonium salt

Question 34

Why do amines reacting with halogenoalkanes not seem to be a good method of preparation?

Answer 34

As it is likely a mixture of primary, secondary, tertiary and quaternary amines will be produced

Question 35

What would happen if you had an excess of halogenoalkane?

Answer 35

The full sequence would likely occur for most, producing mostly quaternary ammonium salts

Question 36

Why are amines able to react with copper(II) ions?

Answer 36

They can act as bases (proton acceptor and electron donator)

Question 37

What observation will initially be seen from the reaction of amines with copper(II) ions?

Answer 37

A light blue precipitate will be formed

Question 38

What observation will then be seen with excess amine after the light blue precipitate has been formed?

Answer 38

The light blue precipitate will dissolve and a deep blue solution will emerge

Question 39

What happens in the reaction between amines and copper(II) ions in the formation of the light blue precipitate?

Answer 39

The 2 amines act as proton acceptors, receiving two hydrogens from the copper complex

Question 40

What is the equation for the reaction between amines and copper(II) complex in the formation of the light blue precipitate?

Answer 40

[Cu(H2O)6]2+ + 2CH3NH2 -> [Cu(H2O)4(OH)2] + 2CH3NH3+

Question 41

What happens in the reaction amines and the copper(II) complex in the formation of the deep blue solution?

Answer 41

The complex formed from the first reaction reacts with 4 more amines, which replace 2 H2Os and 2 OHs that were previously around the copper ion

Question 42

What is the equation for the reaction amines and the copper(II) complex in the formation of the deep blue solution?

Answer 42

[Cu(H2O)4(OH)2] + 4CH3NH2 -> [Cu(CH3NH2)4(H2O)2] + 2H2O + 2OH-

Question 43

What is used in industry as LiAlH4 is too expensive?

Answer 43

Hydrogen gas with a metal catalyst