1. Specification from OCR
Explain the basicity of amines in terms of proton acceptance by the nitrogen lone pair.
Describe the reactions of amines with acids to form salts
Describe the preparation of:
i) aliphatic amines by substitution of halogenalkanes with excess ethanolic ammonia
ii) aromatic amines by reduction of nitroarenes using tin and conc. hydrochloric acid
Describe the synthesis of an azo-dye
State the use of reactions in the formation of dyestuffs

2. Amines Amines are essentially molecules of ammonia
One or more of the hydrogen atoms have been replaced with an alkyl group.

3. 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

4. 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)

5. 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.

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

7. Amines as bases Bases are proton acceptors.
Amines don’t actually accept protons, they donate a lone pair to the hydrogen atom to form a dative bond.
Ammonia and bases can do this with any suitable acid to give a salt.

8. 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

9. 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

10. 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

11. BASIC PROPERTIES
The strength of a weak base will depend on whether the substituents are electron- relasing or withdrawing
Compound Formula Comments
ammonia NH3
methylamine CH3NH2 methyl group is electron releasing
phenylamine C6H5NH2 electrons delocalised into the ring
strongest base > > weakest base

12. 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)

13. The preparation of amines

14. 1. PREPARATION OF ALIPHATIC AMINES
Aliphatic amines can be prepared from substitution of halogenoalkanes with excess ethanolic ammonia
Reagent Excess alcoholic ammonia
Conditions Reflux in aqueous, alcoholic solution under pressure
Product Amine
Nucleophile Ammonia (NH3)
Equation C2H5Br + NH3 (aq / alc) ——> C2H5NH2 + HBr

15. WHY IS THE AMMONIA IN EXCESS??
Reagent Aqueous, alcoholic ammonia (in EXCESS)
Conditions Reflux in aqueous , alcoholic solution under pressure
Product Amine
Nucleophile Ammonia (NH3)
Equation e.g. C2H5Br NH3 (aq / alc) ——> C2H5NH NH4Br
(i) C2H5Br NH3 (aq / alc) ——> C2H5NH HBr
(ii) HBr NH3 (aq / alc) ——> NH4Br
Mechanism
Notes The equation shows two ammonia molecules.
The second ammonia molecule ensures the removal of HBr, because otherwise the salt ethylammonium bromide C2H5NH3+Br¯ will be formed.

16. NUCLEOPHILIC SUBSTITUTION WHY IS THE AMMONIA IN EXCESS??
Why excess ammonia?
A large excess ammonia also ensures that further substitution doesn’t take place - see below
Problem
Amines are also nucleophiles (lone pair on N) and can attack another molecule of halogenoalkane 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, a 2° amine
(C2H5)2NH + C2H5Br ——> HBr (C2H5)3N triethylamine, a 3° amine
(C2H5)3N C2H5Br ——> (C2H5)4N+ Br¯ tetraethylammonium bromide
a quaternary (4°) salt

17. 2. Reduction of nitrobenzene to give phenylamine
Conditions are reflux, this is important in the production of compounds called azo-dyes.

18. H2N C COOH R H H2N C COOH H H2N C COOH CH3 H AMINO ACIDS carboxyl COOH
Structure Amino acids contain 2 functional groups
amine NH2
carboxyl COOH
They all have a similar structure - the identity of R varies
H2N C COOH R H
H2N C COOH H
H2N C COOH
CH3 H

19. 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-aminoethanoic acid

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

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

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

23. 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

24. 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¯

25. 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?

26. + + 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 + +

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. 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 +

29. 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

30. 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

31. 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