C27 - Amines, Amino Acids and Polymers

Question 1

What are amines?

Answer 1

Organic compounds derived from ammonia, where 1+ hydrogen atoms have been replaced by a carbon chain/ring.

Question 2

What’s an aliphatic and aromatic amine?

Answer 2

Aliphatic - the N atom is attached to at least 1 straight or branched chain (alkyl group) e.g. CH3NH2

Aromatic - the N atom is attached to an aromatic ring (aryl group) e.g. C6H5NH2

Question 3

How can amines be classified?

Answer 3

As primary, secondary or tertiary, depending on the number of R groups which the N atom is bonded to.

Question 4

What is the prefix and suffix used for naming amines?

Answer 4

Prefix: amino-

Suffix: -amine

Question 5

Why can amines behave as bases?

Answer 5

They have a lone pair of electrons on the nitrogen atom.

This means the amine can accept a proton by forming a dative covalent bond.

Question 6

How do amines react with acids?

Answer 6

They act as bases and neutralise acids to form a salt.

Question 7

How can a primary amine be formed?

Answer 7

By reacting ammonia (which acts as a nucleophile) with a haloalkane.
This produces an ammonium salt.

Aqueous alkali is then added to generate the amine from the salt.

Question 8

What conditions are needed for the preparation of a primary amine?

Answer 8

Ethanol is needs as a solvent. This prevents any substitution of the halokalkane by water to produce alcohols.

Excess ammonia. This reduces further substitution of the amine group to form secondary and tertiary amines.

Question 9

How are secondary and tertiary amines formed?

Answer 9

Primary amines still have a lone pair of electrons on the N atom which can react further with a haloalkane.

An ammonium salt is again produced which can be form a secondary amine by reacting it with NaOH.

Further substitution would form a tertiary amine.

Question 10

What conditions are needed for the preparation of aromatic amines?

Answer 10

Reflux with tin (Sn) and HCl acid to form the ammonium salt.

This is then reacted with excess NaOH to produce the aromatic amine.

(Tin and HCl act as a reducing agent).

Question 11

How are aromatic amines prepared?

Answer 11

Nitrobenzene (NO2-aromatic compound) is heated under reflux with tin (Sn) and HCl acid to form the ammonium salt (phenylammonium).

This is then reacted with excess NaOH to produce the aromatic amine (phenylamine).

(Tin and HCl act as a reducing agent).

Question 12

What’s the general formula for an alpha amino acid?

Answer 12

RCH(NH2)COOH

Question 13

Are amino acids acidic or basic?

Answer 13

They have acidic COOH groups and basic NH2 groups.

Question 14

What happens when amino acids react with aqueous alkali?

Answer 14

It forms a salt and water (as the alkali reacts with the carboxyl group of the amino acid).

Question 15

What happens when amino acids react with alcohols?

Answer 15

They are easily esterification by heating with an alcohol in the presence of concentrated sulfuric acid.

The alcohol reacts with the carboxyl group to form an ester and water.

Question 16

What’s a chiral centre?

Answer 16

A [carbon] atom that is attached to 4 different atoms or groups of atoms.

Optical isomerism is found in molecules containing a chiral centre.

Question 17

How are optical isomers drawn?

Answer 17

As exact mirror images of each other.

Question 18

What’s condensation polymerisation?

Answer 18

The joining of monomers with loss of a small molecule (usually water, or HCl).

Two different functional groups are needed.

Question 19

How are polyesters made?

Answer 19

By monomers joining together by ester linkages in a long chain in condensation reactions.

They can be made from one monomer containing a carboxyl and alcohol group OR from 2 monomers - one with 2 carboxyl groups (dicarboxylic acid) and another with 2 alcohol groups (diol).

Question 20

How are polyamides formed?

Answer 20

By monomers joining together by amide linkages in a long chain in condensation reactions.

They can be formed from one monomer with a carboxylic acid (or acyl chloride) and an amine group, OR from 2 monomers - one with 2 carboxylic acid (or acyl chloride) groups and the other with 2 amine groups.

Question 21

How are condensation polymers hydrolysed?

Answer 21

Used hot aqueous alkali or hot aqueous acid.

Question 22

What are the products of acid hydrolysis of polyesters?

Answer 22

The monomers used are reproduced (either single monomer with 2 functional groups or two monomers - diol and dicarboxyl).

The acid doesn’t affect either of the products.

Question 23

What are the products of base hydrolysis of polyesters?

Answer 23

The monomers used are reproduced (either single monomer with 2 functional groups or two monomers - diol and dicarboxyl).

However, due to the alkali, the carboxyl groups react to produce salts.

Question 24

What are the products of the acid hydrolysis of polyamides?

Answer 24

The monomers used are reproduced (either single monomer with 2 functional groups or two monomers - dicarboxyl and diamine).

However, the acid reacts with the basic amine groups to form NH3+ (salts).

Question 25

What are the products of base hydrolysis of polyamides?

Answer 25

The monomers used are reproduced (either single monomer with 2 functional groups or two monomers - dicarboxyl and diamine).

However the alkali reacts with the carboxyl groups to form a salt.

Question 26

When does addition polymerisation take place?

Answer 26

When there’s a C=C bond (whereas CONDENSATION polymerisation requires the presence of 2 different functional groups).