4.6 Amines

Question 1

What do all amines contain?

Answer 1

A nitrogen atom bonded directly to a carbon atom of an alkyl or aryl group.

Question 2

how does the bonding of the nitrogen atom affect the naming of the amine?

Answer 2

If the nitrogen atom is bonded to one carbon it’s a primary amine.
If its bonded to 2 carbons its a secondary amine.
If its bonded to three carbons its a tertiary amine.

Question 3

What do aromatic amines contain?

Answer 3

They have an NH2 group bonded directly to the benzene ring.

Question 4

How is a primary amine produced from a halogenoalkane?

Answer 4

Using ammonia (NH3) with a water/ethanol solvent produces an amine.

Question 5

What happens if the mixture of a halogenoalkane and an amine is heated?

Answer 5

Ammonia gas is lost from the mixture thus reducing the yield.

Question 6

what type of mechanism is the formation of amines from halogenoalkanes?

Answer 6

Nucleophilic substitution ( draw now)

Question 7

What is one problem with the production of amines from halogenoalkanes and how can it be overcome?

Answer 7

The usual product is not an amine but a salt as the amine and the for example HBr or HCl react to create a salt. This is overcome by heating with a base thus NaOH is used to release the amine .

Question 8

How can you make primary amines from nitriles?

Answer 8

Using a reducing agent like LIAlH4 dissolved in ethoxyethane as a solvent.

Question 9

How are aromatic amines made?

Answer 9

By the reduction of nitrobenzene

the reason this is the only way is because the ring of electrons in benzene repel nucleophiles such as ammonia

Question 10

What are the reducing agents used in the reduction of nitrobenzene to phenylamine?

Answer 10

Usually tin and HCL

commercially hydrogen and nickel

Question 11

Why are amines bases?

Answer 11

Due to the lone pair of electrons on the nitrogen atom, the lone pair can be used to accept a proton by means of a coordinate bond.

Question 12

What makes alkylamines like methylamine stronger bases than ammonia?

Answer 12

Because in alkylamines the alkyl group ‘push’ electrons slightly towards the nitrogen atom, making it more delta negative when compared with ammonia.

Question 13

Why is phenylamine such a weak base compared with other amines?

Answer 13

Because the lone pair of electrons on the nitrogen become to an extent part of the delocalised system of electrons.

Question 14

Why are phenylamines only slightly soluble in water?

Answer 14

Because of the hydrophobic effect of the benzene ring.

Question 15

What does the reaction of a primary amine and an acid chloride produce?

Answer 15

a peptide bond
-N - C -
I II
H O

Question 16

How can cold nitric acid be used as a test to distinguish between aliphatic and aromatic amines?

Answer 16

Aliphatic amines react with nitric(III) acid with the evolution of nitrogen, so bubbles of colourless gas are seen.

For an aromatic amine, e.g. phenylamine, if the temperature is between 0 ˚C and 10˚C, a solution containing the stable benzenediazonium ion is formed. Thus not producing bubbles of gas.

Question 17

Why is nitric acid HNO2 always produced in situ?

Answer 17

Unstable and very reactive

Question 18

How is nitric acid HNO2 produced when needed?

Answer 18

reacting a dilute acid like HCl on sodium nitrate NaNO2,

NaNO2 + HCl -> HNO2 + NaCl

Question 19

how does a primary aliphatic amine react with nitric(III) acid?

Answer 19

Produces nitrogen gas

R-NH2 + HNO2 -> R-OH + N2 + H2O

This is NOT a good route of preparing a primary alcohol from a primary amine, the yield of alcohol is very low and the yield of nitrogen is very high.

Question 20

What does the reaction between a primary aromatic amine and HNO2 look like?

Answer 20

if the temp is between 0-10 degrees then a solution containing the benznediazonium ion is produced.

Question 21

What happens if the reaction between aromatic amines and HNO2 (nitric acid) is done above 10 degrees or below 0 degrees?

Answer 21

If the reaction takes place above 10 degrees then the decomposition of the benznediazonium compound occurs, giving phenol.

if the reaction is done below 0 degrees then the production of the benzenediazonium compound is too slow.

Question 22

What is an azo dye?

Answer 22

Ar-N=N-Ar where Ar is an aromatic ring system.

Question 23

What enables a diazonium ion to be able to attack?

Answer 23

The diazonium ion is a weak electrophile and needs high electron density to attack. The presence of an -OH or -NH2 group bonded to the ring increases the electron density (called activation) enabling the diazonium ion to bond via electrophilic substitution.

Question 24

What is the reaction between a phenol and a benzenediazonium ion usually called and what does it produced and what condition is needed?

Answer 24

This type of reaction is known as coupling and the resulting compound is called an azo dye.
It needs to be done in an alkaline solution (NaOH) and below 10 degrees.

Question 25

Draw out benzenediazonium chloride and benzenediazonium hydrogensulfate:

Answer 25

Carefully drawn

Question 26

Draw out a reaction between a benzenediazonium chloride and a phenol, ensure you include the condition above the arrow:

Answer 26

have u cooked ?

Question 27

Draw out the colour hexagon and state what it shows:

Answer 27

This shows that whichever colour is absorbed, the colour opposite will be the colour (the colour reflected)

Question 28

Write out the wavelengths of all the colours in ROYGBIV except indigo:

Answer 28

A good way of remembering the order is - Very Busy Garden Yesterday Over Robs try and remember that it starts at 380 and ends at 750.

Question 29

What positions does coupling usually occur on?

Answer 29

Position for usually but if the 4-position is already occupied the coupling takes place at the position adjacent to the -OH group in the 1-position.