3.3.11- Amines (PAPER 2)

Question 1

What are amines and how are they named?

Answer 1

Produced when one or more of H atoms on ammonia is replaced with an organic group, can be primary secondary or tertiary (3H replaced- eg trimethylamine)

Question 2

What classification are aromatic amines?

Answer 2

Primary as only one benzene group attached to nitrogen- eg phenylamine

Question 3

What are non-aromatic/ not associated with benzene amines known as?

Answer 3

Aliphatic amines

Question 4

What are cationic surfactants and how do they work?

Answer 4

Quaternary ammonium salts with a long hydrocarbon tail.

The non-polar tail is attracted to the oil/grease. The polar head is attracted to the polar water. This allows water and oil to mix, removing grease from clothing skin and dishes.

Question 5

Why are cationic surfactants used in hair conditioner/ fabric softener?

Answer 5

They have a positive ammonium ion which is attracted to negatively charged fibres and hair, removing static.

Question 6

How do amines act as a base?

Answer 6

Amines have a lone pair of electrons so they can accept a proton, proton bonds to amine by dative covalent bond. Both electrons in bond originate from lone pair on N.

Question 7

What does the strength of the base depend on?

Answer 7

The availability of the lone pair of electrons on the N, the higher the electron density the more readily available the electrons are.

Question 8

Arrange these from weakest to strongest base: ammonia, primary aliphatic amines, aromatic amines

Answer 8

Weakest- strongest
Aromatic amines, ammonia, primary aliphatic amines (no benzene)

Question 9

Why are aromatic amines less basic?

Answer 9

Benzene is an electron withdrawing group so pulls electrons away from N into the ring structure, electron density at N reduces so lone pair availability reduced.

Question 10

Why are primary aliphatic amines more basic?

Answer 10

Alkyl groups are electron pushing groups so push electrons towards N, electron density at N increases so lone pair availability increases.

Question 11

What are the 2 ways aliphatic amines can be made?

Answer 11

By reacting a haloalkane with excess ammonia or reducing a nitrile

Question 12

Outline the mechanism between chloroethane and excess ammonia

Answer 12

Curly arrow from N: on ammonia to d+ C , curly arrow from C-Cl bond to Cl

Cl removed, intermediate formed where NH3 joined to C, N has positive charge, Cl- ion next to

Curly arrow from N: on 2nd ammonia molecule to H next to N, curly arrow from N-H bond to N, one H removed from salt

CH3CH2NH2 formed (primary amine) and NH4+Cl- ammonium chloride salt

Question 13

Why is this method ineffective?

Answer 13

Primary amines still have a lone pair on the N so can act as a nucleophile so the amine can react with any remaining haloalkanes to produce secondary amine, this can react further to make tertiary or quaternary salt.

Instead of 2 ammonia molecules we use 2 amine molecules

Question 14

What is the equation for primary amine methylamine reacting with chloroethane to form secondary amine?

Answer 14

2CH3NH2 + CH3CH2Cl —–> CH3NHCH2CH3 + CH3NH3+Cl-

Question 15

What are the 2 ways we can reduce nitriles via hydrogenation to produce amines?

Answer 15

LiAlH4 a reducing agent, and acidic conditions

or

Combination of nickel and hydrogen (catalytic hydrogenation)

Question 16

What is general equation for producing amines from hydrogen and nickel?

Answer 16

R-CH2-C≡N + 2H2 —-> R- CH2- CH2NH2

high temp+ pressure

Question 17

What is general equation for producing amines from strong reducing agent LiAlH4?

Answer 17

R-CH2-C≡N + 4 [H] —–> R-CH2-CH2NH2

more expensive as LiAlH4 is expensive so not used in industry

[H] symbolises strong reducing agent dissolved in non-aqueous solvent like dry ether.

Question 18

How are aromatic amines made and what are they used for?

Answer 18

Made by reducing nitrocompounds like nitrobenzene, used to make pharmaceuticals and dye stuffs.

Question 19

How do we reduce nitrobenzene to form phenylamine?

Answer 19

Heat nitrobenzene under reflux with concentrated HCl and tin to form salt like C6H5NH3+Cl-

Salt produced is reacted with alkali like NaOH to form aromatic amine like phenylamine

Nitrobenzene (NO2) + 6[H] (2 attach to N, 4 make 2 water molecules as 2 O2 drop off from nitrobenzene) ——> Phenylamine (NH2) + 2H2O

Question 20

What are amides?

Answer 20

Derivatives of carboxylic acids with the functional group -CONH2

C=O
OH replaced by NH2

Question 21

What is an N-substituted amide? acid chloride with primary amine

Answer 21

Where one of the H joined to the N is replaced by an alkyl group