Amines

Question 1

Is a primary aliphatic amine a stronger or weaker base than ammonia, and why?

Answer 1

Stronger, because the alkyl group pushes electrons away onto attached groups, making the nitrogen atom more electron dense, and therefore making the lone pair more available.

Question 2

Is a primary aromatic amine a stronger or weaker base than ammonia, and why?

Answer 2

Weaker, because the bezene ring draws electrons towards itself and the nitrogen atom’s lone pair of electrons gets partially delocalised onto the ring. So, the electron density on the nitrogen decreases, making the lone pair less available.

Question 3

Are amines acidic or basic?

Answer 3

Basic.

Question 4

What are quaternary ammonium salts used as?

Answer 4

Cationic surfactants. These get rid of static and are used in things like fabric conditioners and hair products.

Question 5

What type of reaction occurs when an amine or ammonia reacts with a haloalkane?

Answer 5

Nucleophilic substitution.

Question 6

Explain the mechanism of an amine or ammonia reacting with a haloalkane.

Answer 6

1) The nitrogen forms a bond with the partially positively charged carbon of the C-X bond, and the halogen is released as a negative ion. The nitrogen becomes positively charged.
2) A second nitrogen atom donates its electrons to a hydrogen atom, and the electrons in the N-H bond reatreat back to the nitrogen atom.
3) The ammonium ion then reacts with the halogen to form an ammonium salt.

Question 7

How can we separate primary, secondary, teritiary amines and quaternary ammonium salts?

Answer 7

Fractional distillation.

Question 8

What is the product formed when ammonia or an amine reacts with a haloalkane?

Answer 8

A primary aliphatic amine. Further substitution can occur to produce secondar and tertiary amines, or quaternary ammonium salts.

Question 9

How can we produce a primary aliphatic amine without risk of further substitution?

Answer 9

By reducing a nitrile.

Question 10

Give three ways in which we can reduce a nitrile.

Answer 10

LiAlH4 with dilute acid, or reflux with sodium metal and ethanol. Most commonly used is a nickel catalyst, hydrogen, and high pressure and temperature.

Question 11

Why do we not use LiAlH4 or sodium metal to reduce nitriles in industry?

Answer 11

They are too expensive.

Question 12

How can we produce an aromatic amine?

Answer 12

Reduce a nitro compound.

Question 13

State and explain the conditions for reducing a nitro compound?

Answer 13

Heat under reflux with tin, conc. HCl and sodium hydroxide solution. The alkali comes last, and turns the salt into aromatic amine.