KNOCKHARDY PUBLISHING
2008
SPECIFICATIONS

KNOCKHARDY PUBLISHING
AMINES
INTRODUCTION
This Powerpoint show is one of several produced to help students understand selected topics at AS and A2 level Chemistry. It is based on the requirements of the AQA and OCR specifications but is suitable for other examination boards.
Individual students may use the material at home for revision purposes or it may be used for classroom teaching if an interactive white board is available.
Accompanying notes on this, and the full range of AS and A2 topics, are available from the KNOCKHARDY SCIENCE WEBSITE at...
www.knockhardy.org.uk/sci.htm
Navigation is achieved by...
either clicking on the grey arrows at the foot of each page or using the left and right arrow keys on the keyboard

AMINES
CONTENTS
• Prior knowledge
• Structure and classification
• Nomenclature
• Physical properties
• Basic properties
• Nucleophilic properties
• Amino acids
• Peptides and proteins
• Amides
• Check list

AMINES
Before you start it would be helpful to…

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

Nomenclature
NOMENCLATURE
Named after the groups surrounding the nitrogen + amine
C
2
H
5
NH
2 ethylamine dimethylamine (CH
3
)
2
NH
(CH
3
)
3
N
C
6
H
5
NH
2 trimethylamine phenylamine (aniline)

Reagent
Conditions
Product
Nucleophile
Equation
PREPARATION
Amines can be prepared from halogenoalkanes
Excess , alcoholic ammonia (WHY USE EXCESS?)
Reflux in excess , alcoholic solution under pressure
Amine (or its salt due to a reaction with the acid produced)
Ammonia (NH
3
)
C
2
H
5
Br + NH
3
(alc) ——> C
2
H
5
NH
2
+ HBr ( or C
2
H
5
NH
3
+ Br¯ )

Reagent
Conditions
Product
Nucleophile
Equation
PREPARATION
Amines can be prepared from halogenoalkanes
Excess , alcoholic ammonia (WHY USE EXCESS?)
Reflux in excess, alcoholic solution under pressure
Amine (or its salt due to a reaction with the acid produced)
Ammonia (NH
3
)
C
2
H
5
Br + NH
3
(alc) ——> C
2
H
5
NH
2
+ HBr ( or C
2
H
5
NH
3
+ Br¯ )
WHY USE EXCESS AMMONIA?
Ammonia attacks halogenoalkanes because it has a lone pair and is a nucleophile.
The amine produced also has a lone pair C
2
H
5
NH
2 so can also attack a halogenoalkane; this leads to the formation of substituted amines.
Using excess ammonia ensures that all the halogenoalkane molecules react with the ammonia before having the chance to react with any amines produced.

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
2
+ H + ——> RNH
3
+
NUCLEOPHILES - provide a lone pair to attack an electron deficient centre

Boiling point
PHYSICAL PROPERTIES
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.

BASIC PROPERTIES
Bases The lone pair on the nitrogen atom makes amines basic;
RNH
2
+ H + ——> RNH
3
+ 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

BASIC PROPERTIES
Bases The lone pair on the nitrogen atom makes amines basic;
RNH
2
+ H + ——> RNH
3
+ 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
C
6
H
5
H
N :
H

BASIC PROPERTIES
Bases The lone pair on the nitrogen atom makes amines basic;
RNH
2
+ H + ——> RNH
3
+ 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
C
6
H
5
H
N :
H electron releasing substituents (CH
3 groups) increase basicity as the electron density is increased and the lone pair is more effective
CH
3
H
N :
H

Measurement
BASIC PROPERTIES the strength of a weak base is depicted by its pK b the smaller the pK b the stronger the base value the pK a value can also be used; it is worked out by applying pK a
+ pK b the smaller the pK b
, the larger the pK a
.
= 14
Compound ammonia methylamine phenylamine
Formula
NH
3
CH
3
NH
2
C
6
H
5
NH
2 pK
4.76
3.36
9.38
b
Comments methyl group is electron releasing electrons delocalised into the ring strongest base methylamine > ammonia > phenylamine weakest base smallest pK b largest pK b

CHEMICAL REACTIONS WEAK BASES
Water Amines which dissolve in water produce weak alkaline solutions
CH
3
NH
2
(g) + H
2
O(l) CH
3
NH
3
+ (aq) + OH¯(aq)
Acids Amines react with acids to produce salts.
C
6
H
5
NH
2
(l) + HCl(aq)
——> C
6
H
5
NH
3
+ 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
C
6
H
5
NH
3
+ Cl¯(aq) + NaOH(aq) ——> C
6
H
5
NH
2
(l) + NaCl(aq) + H
2
O(l)

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

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 .
C
2
H
5
NH
2
+ C
2
H
5
Br ——> HBr + (C
2
H
5
)
2
NH diethylamine, 2 ° amine

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.
C
2
H
5
NH
2
+ C
2
H
5
Br ——> HBr + (C
2
H
5
)
2
NH diethylamine, 2 ° amine
(C
2
H
5
)
2
NH + C
2
H
5
Br
——> HBr + (C
2
H
5
)
3
N triethylamine, 3
° amine

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 .
C
2
H
5
NH
2
+ C
2
H
5
Br ——> HBr + (C
2
H
5
)
2
NH diethylamine, 2 ° amine
(C
2
H
5
)
2
NH + C
2
H
5
Br
——> HBr + (C
2
H
5
)
3
N triethylamine, 3
° amine
(C
2
H
5
)
3
N + C
2
H
5
Br ——> (C
2
H
5
)
4
N + Br¯ tetraethylammonium bromide a quaternary (4 °) salt

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.
C
2
H
5
NH
2
+ C
2
H
5
Br ——> HBr + (C
2
H
5
)
2
NH diethylamine, 2 ° amine
(C
2
H
5
)
2
NH + C
2
H
5
Br
——> HBr + (C
2
H
5
)
3
N triethylamine, 3
° amine
(C
2
H
5
)
3
N + C
2
H
5
Br ——> (C
2
H
5
)
4
N + 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. [CH
3
(CH
2
)
17
]
2
N + (CH
3
)
2
Cl¯

AMINO ACIDS
Structure Amino acids contain 2 functional groups amine NH
2 carboxyl COOH
R
1
H
2
N C COOH
R
2
They all have a similar structure - the identity of R
1 and R
2 vary
H
H
2
N C COOH
H
H
H
2
N C COOH
CH
3

AMINO ACIDS – OPTICAL ISOMERISM
Amino acids can exist as optical isomers
If they have different R
1 and R
2 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
H
H
2
N C COOH
CH
3
Glycine doesn’t exhibit optical isomerism as there are two H attached to the C atom
H
H
2
N C COOH
H
GLYCINE
2-aminoethanoic acid

Zwitterion
AMINO ACIDS ZWITTERIONS
• 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
R
1
H
3
N + C COO ¯
R
2

AMINO ACIDS ACID-BASE PROPERTIES
• amino acids possess acidic and basic properties
• this is due to the two functional groups
• COOH gives acidic properties
• NH
2 gives basic properties
• they form salts when treated with acids or alkalis.
R
1
H
2
N C COOH
R
2

AMINO ACIDS ACID-BASE PROPERTIES
Basic properties: with H + with HCl
HOOCCH
2
NH
2
HOOCCH
2
NH
2
+ H + ——> HOOCCH
2
NH
3
+
+ HCl ——> HOOCCH
2
NH
3
+ Cl¯
Acidic properties: with OH¯ with NaOH
HOOCCH
2
NH
2
+ OH¯ ——> ¯OOCCH
2
NH
2
+ H
2
O
HOOCCH
2
NH
2
+ NaOH ——> Na+ ¯OOCCH
2
NH
2
+ H
2
O

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

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
H +
NaOH
OH¯
NH
2 becomes NH
3
+ Cl¯
NH
2 becomes NH
3
+
COOH becomes COO¯ Na +
COOH becomes
COO¯

PEPTIDES HYDROLYSIS
Peptides are broken down into their constituent amino acids by hydrolysis
H
CH
3
H
H
CH
3
H
2
N C CO NH C CO NH C COOH
CH
3
Which amino acids are formed?

PEPTIDES HYDROLYSIS
Peptides are broken down into their constituent amino acids by hydrolysis
H
CH
3
H
H
CH
3
H
2
N C CO NH C CO NH C COOH
CH
3
H H CH
3
H
2
N C COOH + H
2
N C COOH + H
2
N C COOH
CH
3
H CH
3

PEPTIDES HYDROLYSIS
Peptides are broken down into their constituent amino acids by hydrolysis
H H H
H
2
N C CO NH C CO NH C COOH
CH
3
H CH
3
Which amino acids are formed?

PEPTIDES HYDROLYSIS
Peptides are broken down into their constituent amino acids by hydrolysis
H H H
H
2
N C CO NH C CO NH C COOH
CH
3
H CH
3
H
2 x H
2
N C COOH
CH
3
+
H
H
2
N C COOH
H

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

Structure
AMIDES derivatives of carboxylic acids amide group is -CONH
2
Nomenclature White crystalline solids named from the corresponding acid
(remove oic acid, add amide)
CH
3
CONH
2 ethanamide (acetamide)
C
2
H
5
CONHC
6
H
5
N - phenyl propanamide the N tells you the substituent is on the nitrogen
Nylons are examples of polyamides
Preparation Acyl chloride + ammonia
CH
3
COCl + NH ethanoyl chloride
3
——> CH
3
CONH ethanamide
2
+ HCl

AMIDES CHEMICAL PROPERTIES
Hydrolysis general reaction CH
3
CONH
2 acidic soln. CH
3
CONH
2 alkaline soln. CH
3
CONH
2
+ H
2
O ——> CH
3
COOH + NH
3
+ H
2
O + HCl ——> CH
+ NaOH
——> CH
3
3
COOH + NH
COONa + NH
3
4
Cl
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: CH
3
CONH
2
+ 4[H]
——> CH
3
CH
2
NH
2
+ H
2
O

© 2009 JONATHAN HOPTON & KNOCKHARDY PUBLISHING