Amines, amino acids and polymers

Question 1

What are amines?

Answer 1

Organic compounds, derived from NH3, where one or more hydrogen atoms in ammonia have been replaced by a carbon chain or ring.
In an aromatic amine, the nitrogen atom is attached to an aromatic ring.

Question 2

How are amines classified?

Answer 2

Primary amines have 1 alkyl or aryl group attached to the nitrogen atom.
Secondary amines have 2 alkyl groups attached to the nitrogen atom.
Tertiary amines have 3 alkyl groups attached to the nitrogen atom.

Question 3

What is serotonin?

Answer 3

An amine that acts as a neurotransmitter, which controls appetite, sleep, memory and learning, temperature regulation, muscle contraction, and depression.

Question 4

What is pseudoephedrine?

Answer 4

An amine that is an active ingredient in decongestion medications such as in nose drops and in cold remedies.
It works by shrinking nasal membranes and inhibiting nasal secretions.

Question 5

How are primary amines named?

Answer 5

If the NH2 group is at the end of the carbon chain, the suffix -amine is added to the name of the alkyl chain.
If the amine group is on any other carbon atom, the prefix amino- and a number is added to indicate the position of the amine group.

Question 6

How are secondary and tertiary amines named?

Answer 6

If it contains the same alkyl group, the prefixes di or tri are used to indicate the number of alkyl groups attached to the nitrogen atom.
When 2 or more different groups are attached to a nitrogen atom, the compound is named as a N-substituted derivative of the larger group.
E.g. N-methylpropylamine.
N-ethyl-N-methylpropylamine.

Question 7

How are amines bases?

Answer 7

Amines have a lone pair of electrons on the nitrogen atom so can accept a proton.
When an amine accepts a proton, a dative covalent bond is formed between the lone pair and the proton.

Question 8

What is salt formation from amines?

Answer 8

Amines can neutralise acids to make salts.
Propylamine reacts with hydrochloric acid to form propylammonium chloride.
CH3CH2CH2NH2 + HCl –> CH3CH2CH2NH3+Cl-
Ethylamine reacts with sulfuric acid to form ethylammonium sulfate.
2CH3CH2NH2 + H2SO4 –> (CH3CH2NH3+)2SO42-

Question 9

What is the formation of primary amines?

Answer 9

The lone pair of electrons on the nitrogen means ammonia acts as a nucleophile in a substitution reaction with a haloalkane, to produce an ammonium salt.
Aqueous alkali is then added to form the amine.

Question 10

What are the conditions for forming amines?

Answer 10

Hot ethanol is used as a solvent to prevent any substitution of the haloalkane by water to produce alcohols.
Excess ammonia is used to reduce further substitutions of the amine to form secondary and tertiary amines.

Question 11

What is an example of forming a primary amine?

Answer 11

CH3CH2CH2Cl + NH3 –> CH3CH2CH2NH3+Cl-
1-chloropropane + ammonia –> propylammonium chloride
CH3CH2CH2NH3+Cl- + NaOH –> CH3CH2CH2NH2 + NaCl + H2O
Propylammonium chloride + NaOH –> Propylamine

Question 12

What is formation of a secondary or tertiary amine?

Answer 12

Primary amines formed from nucleophilic substitution of a haloalkane still have a lone pair of electrons on the nitrogen atom that can react with a haloalkane to form a secondary amine.
Tertiary amines can be formed by further reaction of the secondary amine.

Question 13

What is an example of forming a secondary and tertiary amine?

Answer 13

CH3CH2CH2Cl + CH3CH2CH2NH2 –> (CH3CH2CH2)2NH2+Cl-
1-chloropropane + propylamine –> dipropylammonium chloride salt
(CH3CH2CH2)2NH2+Cl- + NaOH –> (CH3CH2CH2)2NH + NaCl + H2O
forms dipropylamine, and then tripropylamine if further substituted.

Question 14

What is the preparation of aromatic amines?

Answer 14

Phenylamine is made by the reduction of nitrobenzene, by heating it under reflux with tin and hydrochloric acid.
This forms phenylammonium chloride (salt), which is reacted with excess NaOH to form phenylamine.
C6H5NO2 + 6[H] –Sn/conc HCl, excess NaOH –> C6H5NH2 + 2H2O

Question 15

How do you form an amine from a nitrile?

Answer 15

Nitriles can be reduced to amines by reacting with hydrogen and a Nickel catalyst.
CH3CH2C≡N + 2H2 —> CH3CH2CH2NH2

Question 16

What is an amino acid?

Answer 16

An organic compound containing a carboxylic acid and an amine.
General formula is RCH(NH2)COOH.
α-amino acids have the amine attached to the second carbon atom, next to the COOH group, which differ by the side chain.

Question 17

What is the reaction of the carboxylic acid group in amino acids with aqueous alkalis?

Answer 17

Aminoethanoic acid + sodium hydroxide –> sodium salt + water
CH2(NH2)COOH + NaOH –> CH2(NH2)COO-Na+ + H2O
Can also react with KOH.

Question 18

What is the esterification of the carboxylic acid in amino acids?

Answer 18

Amino acids can be esterified by heating with an alcohol with concentrated H2SO4.
The carboxylic acid is esterified, and the acidic conditions protonate the amine group. (forms NH3+)

Question 19

What are amides?

Answer 19

The products of the reaction of acyl chlorides with ammonia and amines.
In nature, amine and carboxylic acid groups of amino acids are bonded together to form amide groups.
Named propanamide
N-methylethanamide
N,N-dimethylmethanamide

Question 20

What are optical isomers?

Answer 20

Stereoisomers that are non-superimposable mirror images of each other, or enantiomers.
For each chiral centre* - a carbon atom attached to four different groups - there is a pair of optical isomers.

Question 21

What is chirality of amino acids?

Answer 21

Apart from glycine, H2NCH2COOH, all α-amino acids have a chiral carbon atom.

Question 22

What is condensation polymerisation?

Answer 22

The joining of monomers with loss of a small molecule, usually water or HCl.
Polyesters and polyamides are important condensation polymers.

Question 23

What is the formation of polyesters?

Answer 23

Has ester linkages formed from esterification between a carboxylic acid or acyl chloride and an alcohol functional group:
From one monomer with 2 different functional groups.
From two monomers each containing two functional groups (dicarboxylic acids or dihydroxyl groups.)

Question 24

What are the uses of polyesters?

Answer 24

Terylene (PET) is used in clothing and plastic PET bottles.
Polyesters are used in electrical insulation.

Question 25

What is the formation of polyamides?

Answer 25

Has amide linkages formed from condensation of a carboxylic acid and amine group:
From one monomer with two functional groups to form a polypeptide.
From two monomers with two functional groups (dicarboxylic acid and diamine).

Question 26

What are the uses of polyamides?

Answer 26

Nylon is used in clothing, fibres, fishing nets, ropes, parachutes, and fabrics.

Question 27

What is hydrolysing polyesters?

Answer 27

Base hydrolysis using hot aqueous NaOH:
Forms COO-Na+ group and the alcohol.
Acid hydrolysis using hot aqueous HCl:
Forms the carboxylic acid and the alcohol.

Question 28

What is hydrolysing polyamides?

Answer 28

Base hydrolysis using hot aqueous NaOH:
Forms COO-Na+ group and the amide.
Acid hydrolysis using hot aqueous HCl:
Carboxylic acid and the amide salt RNH3+ (can be RNH3+Cl-)

Question 29

How can you identify the monomers and repeat units in polymerisation?

Answer 29

Addition polymerisation - monomer has a double bond, backbone of polymer is a continuous chain of carbon atoms.
Condensation polymerisation - two monomers, with two functional groups, one monomer two different functional groups. Polymer contains amide or ester linkages.