1. A guide for A level students KNOCKHARDY PUBLISHING
THE CHEMISTRY
OF AMINES
A guide for A level students
KNOCKHARDY PUBLISHING

2. KNOCKHARDY PUBLISHING
AMINES
INTRODUCTION
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3. AMINES CONTENTS Prior knowledge Structure and classification
Nomenclature
Physical properties
Basic properties
Nucleophilic properties
Amino acids
Peptides and proteins
Amides
Check list

4. Before you start it would be helpful to…
AMINES
Before you start it would be helpful to…
know the functional groups found in organic chemistry
know the arrangement of bonds around atoms
recall and explain nucleophilic substitution reactions

5. STRUCTURE & CLASSIFICATION
Structure Contain the NH2 group
Classification
primary (1°) amines secondary (2°) amines
tertiary (3°) amines quarternary (4°) ammonium salts
Aliphatic methylamine, ethylamine, dimethylamine
Aromatic NH2 group is attached directly to the benzene ring (phenylamine)
R N: H
R N: R H
R N: R R +
R N R

6. NOMENCLATURE (CH3)2NH dimethylamine (CH3)3N trimethylamine
Nomenclature Named after the groups surrounding the nitrogen + amine
C2H5NH2 ethylamine
(CH3)2NH dimethylamine
(CH3)3N trimethylamine
C6H5NH2 phenylamine (aniline)

7. Amines can be prepared from halogenoalkanes
PREPARATION
Amines can be prepared from halogenoalkanes
Reagent Aqueous, alcoholic ammonia
Conditions Reflux in aqueous, alcoholic solution under pressure
Product Amine (or its salt due to a reaction with the acid produced)
Nucleophile Ammonia (NH3)
Equation C2H5Br + NH3 (aq / alc) ——> C2H5NH2 + HBr ( or C2H5NH3+Br¯ )

8. PHYSICAL PROPERTIES
The LONE PAIR on the nitrogen atom in 1°, 2° and 3° amines makes them ...
LEWIS BASES - they can be lone pair donors
BRØNSTED-LOWRY BASES - they can be proton acceptors
RNH H+ ——> RNH3+
NUCLEOPHILES - provide a lone pair to attack an electron deficient centre

9. PHYSICAL PROPERTIES
Boiling point Boiling points increase with molecular mass
Amines have higher boiling
points than corresponding
alkanes because of their
intermolecular hydrogen bonding
Quarternary ammonium
salts are ionic and exist as salts
Solubility Lower mass compounds are
soluble in water due to hydrogen
bonding with the solvent.
Solubility decreases as the
molecules get heavier.
Soluble in organic solvents.

10. BASIC PROPERTIES
Bases The lone pair on the nitrogen atom makes amines basic;
RNH H+ ——> RNH a proton acceptor
Strength depends on the availability of the lone pair and its ability to pick up protons
• the greater the electron density on the N, the better it can pick up protons
• this is affected by the groups attached to the nitrogen

11. BASIC PROPERTIES
Bases The lone pair on the nitrogen atom makes amines basic;
RNH H+ ——> RNH a proton acceptor
Strength depends on the availability of the lone pair and its ability to pick up protons
• the greater the electron density on the N, the better it can pick up protons
• this is affected by the groups attached to the nitrogen
electron withdrawing substituents (benzene rings)
decrease basicity as the electron density on N is
lowered and the lone pair is less effective H
C6H N: H

12. BASIC PROPERTIES C6H5 N: CH3 N:
Bases The lone pair on the nitrogen atom makes amines basic;
RNH H+ ——> RNH a proton acceptor
Strength depends on the availability of the lone pair and its ability to pick up protons
• the greater the electron density on the N, the better it can pick up protons
• this is affected by the groups attached to the nitrogen
electron withdrawing substituents (benzene rings)
decrease basicity as the electron density on N is
lowered and the lone pair is less effective
electron releasing substituents (CH3 groups)
increase basicity as the electron density is
increased and the lone pair is more effective H
C6H N: H H
CH N: H

13. BASIC PROPERTIES
Measurement the strength of a weak base is depicted by its pKb value
the smaller the pKb the stronger the base
the pKa value can also be used;
it is worked out by applying pKa + pKb = 14
the smaller the pKb, the larger the pKa.
Compound Formula pKb Comments
ammonia NH
methylamine CH3NH methyl group is electron releasing
phenylamine C6H5NH electrons delocalised into the ring
strongest base methylamine > ammonia > phenylamine weakest base
smallest pKb largest pKb

14. CHEMICAL REACTIONS - WEAK BASES
Water Amines which dissolve in water produce weak alkaline solutions
CH3NH2(g) H2O(l) CH3NH3+(aq) OH¯(aq)
Acids Amines react with acids to produce salts.
C6H5NH2(l) HCl(aq) ——> C6H5NH3+Cl¯(aq) phenylammonium chloride
This reaction allows one to dissolve an amine in water as its salt.
Addition of aqueous sodium hydroxide liberates the free base from its salt
C6H5NH3+Cl¯(aq) NaOH(aq) ——> C6H5NH2(l) NaCl(aq) + H2O(l)

15. CHEMICAL REACTIONS - NUCLEOPHILIC
Due to their lone pair, amines react as nucleophiles
Reagent Product Mechanism
haloalkanes substituted amines nucleophilic substitution
acyl chlorides N-substituted amides addition-elimination

16. NUCLEOPHILIC SUBSTITUTION
HALOALKANES
Amines are also nucleophiles (lone pair on N) and can attack halogenoalkanes to produce a 2° amine. This too is a nucleophile and can react further producing a 3° amine and, eventually an ionic quarternary ammonium salt.
C2H5NH C2H5Br ——> HBr (C2H5)2NH diethylamine, 2° amine

17. NUCLEOPHILIC SUBSTITUTION
HALOALKANES
Amines are also nucleophiles (lone pair on N) and can attack halogenoalkanes to produce a 2° amine. This too is a nucleophile and can react further producing a 3° amine and, eventually an ionic quarternary ammonium salt.
C2H5NH C2H5Br ——> HBr (C2H5)2NH diethylamine, 2° amine
(C2H5)2NH + C2H5Br ——> HBr (C2H5)3N triethylamine, 3° amine

18. NUCLEOPHILIC SUBSTITUTION
HALOALKANES
Amines are also nucleophiles (lone pair on N) and can attack halogenoalkanes to produce a 2° amine. This too is a nucleophile and can react further producing a 3° amine and, eventually an ionic quarternary ammonium salt.
C2H5NH C2H5Br ——> HBr (C2H5)2NH diethylamine, 2° amine
(C2H5)2NH + C2H5Br ——> HBr (C2H5)3N triethylamine, 3° amine
(C2H5)3N C2H5Br ——> (C2H5)4N+ Br¯ tetraethylammonium bromide
a quaternary (4°) salt

19. NUCLEOPHILIC SUBSTITUTION
HALOALKANES
Amines are also nucleophiles (lone pair on N) and can attack halogenoalkanes to produce a 2° amine. This too is a nucleophile and can react further producing a 3° amine and, eventually an ionic quarternary ammonium salt.
C2H5NH C2H5Br ——> HBr (C2H5)2NH diethylamine, 2° amine
(C2H5)2NH + C2H5Br ——> HBr (C2H5)3N triethylamine, 3° amine
(C2H5)3N C2H5Br ——> (C2H5)4N+ Br¯ tetraethylammonium bromide
a quaternary (4°) salt
Uses Quarternary ammonium salts with long chain alkyl groups are used
as cationic surfactants in fabric softening e.g. [CH3(CH2)17]2N+(CH3)2 Cl¯

20. H2N C COOH R2 R1 H2N C COOH H H2N C COOH CH3 H AMINO ACIDS
Structure Amino acids contain 2 functional groups
amine NH2
carboxyl COOH
They all have a similar structure - the identity of R1 and R2 vary
H2N C COOH R2 R1
H2N C COOH H
H2N C COOH
CH3 H

21. AMINO ACIDS – OPTICAL ISOMERISM
Amino acids can exist as optical isomers
If they have different R1 and R2 groups
Optical isomers exist when a molecule
Contains an asymmetric carbon atom
Asymmetric carbon atoms have four
different atoms or groups attached
Two isomers are formed - one rotates plane
polarised light to the left, one rotates it to the right
Glycine doesn’t exhibit optical isomerism as
there are two H attached to the C atom
H2N C COOH
CH3 H
H2N C COOH H
GLYCINE
2-aminopropanoic acid

22. AMINO ACIDS - ZWITTERIONS
Zwitterion • a dipolar ion
• has a plus and a minus charge in its structure (see below)
• amino acids exist as zwitterions
• give increased inter-molecular forces
• melting and boiling points are higher
H3N+ C COO¯ R2 R1

23. AMINO ACIDS - ACID-BASE PROPERTIES
• amino acids possess acidic and basic properties
• this is due to the two functional groups (see above)
• COOH gives acidic properties
• NH2 gives basic properties
• they form salts when treated with acids or alkalis.
H2N C COOH R2 R1

24. AMINO ACIDS - ACID-BASE PROPERTIES
Acidic properties:
with H+ HOOCCH2NH H ——> HOOCCH2NH3+
with HCl HOOCCH2NH HCl ——> HOOCCH2NH3+ Cl¯
Basic properties:
with OH¯ HOOCCH2NH OH¯ ——> ¯OOCCH2NH H2O
with NaOH HOOCCH2NH NaOH ——> Na+ ¯OOCCH2NH H2O

25. PEPTIDES - FORMATION & STRUCTURE
Amino acids can join together to form peptides via an amide or peptide link
2 amino acids joined dipeptide
3 amino acids joined tripeptide
many amino acids joined polypeptide
a dipeptide

26. PEPTIDES - HYDROLYSIS
Peptides are broken down into their constituent amino acids by hydrolysis
• attack takes place at the slightly positive C of the C=O
• the C-N bond is broken
• hydrolysis with water is very slow
• hydrolysis in alkaline/acid conditions is quicker
• hydrolysis in acid/alkaline conditions (e.g. NaOH) will produce salts
with HCl NH2 becomes NH3+Cl¯
H+ NH2 becomes NH3+
NaOH COOH becomes COO¯ Na+
OH¯ COOH becomes COO¯

27. Which amino acids are formed?
PEPTIDES - HYDROLYSIS
Peptides are broken down into their constituent amino acids by hydrolysis
H2N C CO
CH3 H
NH C CO
NH C COOH
Which amino acids are formed?

28. + + H2N C CO CH3 H NH C CO NH C COOH CH3 H H2N C COOH H H2N C COOH CH3
PEPTIDES - HYDROLYSIS
Peptides are broken down into their constituent amino acids by hydrolysis
H2N C CO
CH3 H
NH C CO
NH C COOH
CH3 H
H2N C COOH H
H2N C COOH
CH3
H2N C COOH + +

29. Which amino acids are formed?
PEPTIDES - HYDROLYSIS
Peptides are broken down into their constituent amino acids by hydrolysis
H2N C CO
CH3 H
NH C CO
NH C COOH
Which amino acids are formed?

30. 2 x + H2N C CO CH3 H NH C CO NH C COOH CH3 H H2N C COOH H H2N C COOH
PEPTIDES - HYDROLYSIS
Peptides are broken down into their constituent amino acids by hydrolysis
H2N C CO
CH3 H
NH C CO
NH C COOH
CH3 H
H2N C COOH H
H2N C COOH
2 x +

31. PROTEINS • are polypeptides with high molecular masses
• chains can be lined up with each other
• the C=O and N-H bonds are polar due to a difference in electronegativity
• hydrogen bonding exists between chains
dotted lines represent hydrogen bonding

32. AMIDES Structure derivatives of carboxylic acids amide group is -CONH2
Nomenclature White crystalline solids named from the corresponding acid
(remove oic acid, add amide)
CH3CONH2 ethanamide (acetamide)
C2H5CONHC6H5 N - phenyl propanamide - the N tells you the
substituent is on
the nitrogen
Nylons are examples of polyamides
Preparation Acyl chloride + ammonia
CH3COCl NH3 ——> CH3CONH HCl
ethanoyl chloride ethanamide

33. AMIDES - CHEMICAL PROPERTIES
Hydrolysis
general reaction CH3CONH H2O ——> CH3COOH NH3
acidic soln CH3CONH H2O HCl ——> CH3COOH NH4Cl
alkaline soln CH3CONH NaOH ——> CH3COONa NH3
Identification Warming an amide with dilute sodium hydroxide solution and
testing for the evolution of ammonia using moist red litmus paper
is used as a simple test for amides.
Reduction
Reduced to primary amines: CH3CONH [H] ——> CH3CH2NH2 + H2O

34. What should you be able to do?
REVISION CHECK
What should you be able to do?
Recall the structural types and nomenclature of amines
Explain and understand the basic properties of amines
Recall and explain the nucleophilic properties of amines
Recall the structure and general properties of amino acids, proteins and peptides
Understand why amino acids can exhibit optical activity
Work out the products from the hydrolysis of a peptide
Recall the structure, nomenclature, preparation and simple properties of amides
CAN YOU DO ALL OF THESE? YES NO

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37. © 2003 JONATHAN HOPTON & KNOCKHARDY PUBLISHING
THE CHEMISTRY
OF AMINES
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