Amines, amino acids and polymers

Question 1

What are amines?

Answer 1

Amine are organic compounds, derived from ammonia, NH3, in which one or more hydrogen atoms in ammonia have been replaced by a carbon chain or ring

Question 2

What is an aliphatic amine?

Answer 2

• In an aliphatic amine, the nitrogen atom is attached to at least on straight or branched carbon chain
• Methylamine Ch3nH2 is the simplest aliphatic amine with one methyl group attached to the nitrogen atom

Question 3

What is an aromatic amine?

Answer 3

• In aromatic amines, the nitrogen atom is attached to an aromatic ring (aryl group, Ar)
• Phenylamine C6H5NH2 is the simplest aromatic amine with a phenyl C6H5 group attached to the nitrogen atom

Question 4

How are amines classified?

Answer 4

-Amines are classified as primary’s secondary or tertiary by the number of alkyl or aryl groups attached to the nitrogen atom

Question 5

How are amines named?

Answer 5

-Amines are named as if the amine is the longest chain and the carbon atoms are the side chain

Question 6

How do you name a primary amine with the -NH2 group on the end of the chain?

Answer 6

Adding the suffix -amine to the name of the alkyl chain

Question 7

How do you name a primary amine that contains an amine group on any other carbon but carbon 1?

Answer 7

Using the prefix amino- and a number is added to indicate the position of the amine group along that chain

Question 8

How do you name secondary or tertiary amines containing the same alkyl group?

Answer 8

The prefixes, di- or tro- are used to indicate the number of alkyl groups attached to the nitrogen atom e.g. (CH3)2NH is dimethylamine

Question 9

How do you name amines when two or more different groups are attached to a nitrogen atom?

Answer 9

It is named as an N-substituted derivative of the larger group e.g. Ch3N(CH2CH3)CH2Ch2CH3,is N-ethyl-N-methylpropylamine

Question 10

What does the presence of the nitrogen atom give amines?

Answer 10

• They can hydrogen bond
• This means that they often have higher than expected boiling points
• And they are soluble in water
• This is of special importance in biological systems

Question 11

How does the lone pair also affect amines?

Answer 11

The lone pair of the nitrogen atom means that they act as bases

Question 12

How do amines act as bases?

Answer 12

• The formation of a dative bond to H+ ions (dative covalent bond between lone pair of electrons on the nitrogen atom and the proton)
• As a result they are proton acceptors
• When an amine reacts with an acid it is a neutralisation reaction and a salt is formed

Question 13

Describe the preparation of primary amines (aliphatic amines)

Answer 13

1. Ammonia has a lone pair of electrons on the nitrogen atom which allows ammonia to act as a nucleophile in a substitution reaction with a haloalkane
2. The product of this reaction is an ammonium salt
3. Aqueous alkali is then added to generate the amine from the salt

Question 14

What is needed for the preparation of a primary amine and why?

Answer 14

1. Ethanol is used as a solvent and this prevents any substitution of the haloalkane by water to produce alcohols
2. Excess ammonia is used and this reduced further substitution of the amine group to form secondary and tertiary amines

Question 15

Describe the formation of secondary and tertiary amines (aliphatic amines)

Answer 15

1. The secondary amine is obtained from the salt (first step of primary amine) by reacting the product with sodium hydroxide
2. Tertiary amines can be formed by further reactions the secondary amine the secondary amine

Question 16

Why is the formation of primary amines unsuitable for making a pure primary amine?

Answer 16

The product still contains a lone pair of electrons on the nitrogen atom than can react further with a haloalkane to form a secondary amine

Question 17

Describe the preparation of aromatic amines

Answer 17

1. Phenylamine C6H5NH2 is made by reduction of nitrobenzene C6H5NO2
2. Nitrobenzene is heated under reflux with tin and hydrochloric acid to form the ammonium salt, phenyl ammonium chloride, which is then reacted with excess sodium hydroxide to produce the aromatic amine, phenyl amine

Question 18

In the reduction of nitrobenzene what do tin and hydrochloric acid acts as?

Answer 18

A reducing agent