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CHAPTER 9:CHAPTER 9:
NOR AKMALAZURA JANI
- organic derivatives of ammonia with one or more alkyl or aryl
groups bonded to the nitrogen atom.
• Functional group:
• Classification of amines:
Primary amine Secondary amine Tertiary amine
• Primary (1o
) amine: one alkyl or aryl group attached to the
• Secondary (2o
) amine: two alkyl or aryl group attached to the
• Tertiary (3o
) amine: three alkyl or aryl group attached to the
• Quaternary (4o
) amine: an ion in which nitrogen is bonded to
four alkyl or aryl groups and bears a positive charge
• Common names:
- formed from the names of the alkyl groups bonded to nitrogen,
followed by the suffix –amine.
- the prefixes di-, tri-, and tetra- are used to decribe two, three
or four identical substituents.
CH3 CH2 NH2
CH3 CH2 N
• IUPAC names:
- similar to that alcohols.
- the longest continuous chain of carbon atoms determine the root
- the –e in alkane name is changed to –amine, and a number shows
the position of the amino group along the chain.
- other substituents on the carbon chain are given numbers, and
the prefix N- is used for each substituent on nitrogen.
CH3 CH2 CH CH3
CH3 CH2 CH CH3
NHCH3 CH2CH3 CH CH
N-methyl-2-butanamine 2,4, N, N-tetramethyl-3-hexanamine
• The prefix ‘amino’ is used to indicate the presence of an –NH2
group in a molecule containing than one functional group.
• For example,
aminoethanoic acid 2-aminoethanol
• Aromatic amines have an amine group (-NH2) attached directly to
the aromatic ring.
• Aromatic amines known as arylamines.
NAMING AROMATIC PRIMARY AMINES
H2N (CH2)6 NH2
• Compounds with two –NH2 groups are named by adding
the suffix ‘diamine’ to the name of the corresponding
alkane or aromatic compounds.
PHYSICAL PROPERTIES OF AMINES
i) Boiling points:
- the boiling points of amines is increase with increasing relative
- the lower aliphatic amines are gases or low-boiling liquids.
- amines are polar compounds and both primary and secondary
amines associate by intermolecular hydrogen bonding.
* Comparing the boiling points of 1o
- for isomeric amines, the boiling points decreases in the order,
1° amine > 2° amine > 3° amine
- reason: decrease in intermolecular hydrogen bonding.
H CH3 N
boiling point: 48.6
molecular formula: C3H9N
molecular mass: 59
* Comparing the boiling points of amines with other organic
- the boiling points of aliphatic amines are higher than
those of alkanes or haloalkanes of similar relative
molecular mass due to intermolecular hydrogen bonding.
- the N-H bond is more polar than the C-H bond but less
polar than O-H bond. Hydrogen bonding in amines are
weaker than that of alcohols or carboxylic acids. Boiling
points of amines are lower than those corresponding
alcohols or carboxylic acids.
Comparison of boiling points of some organic compounds with similarComparison of boiling points of some organic compounds with similar
molecular weightmolecular weight
alkane < ether < alkyl halide < amine < ketone, aldehyde < alcohol < acid
ii) Solubilities of 1o
- all three classes of aliphatic amines are capable of
forming hydrogen bonds with water molecules.
- the lower amines (with chain length up to four
carbon atoms per molecule) are very soluble in
water because they can form hydrogen bonds with
- the solubilities of amines is decrease with
increasing number of carbon atoms in the chain.
- amines are soluble in organic solvents.
• Amines can act as:
- a nucleophile (a Lewis base) because its lone pair none bonding
electrons can form a bond with an electrophile.
- a Brønsted-Lowry base because it can accept a proton from a
nucleophile electrophile new N-C bond formed
Reaction of an amine as a proton base
base proton acid protonated
Reaction of an amine as a nucleophile
THE BASICITY OF
• Amines are fairly strong base and their aqueous solutions are basic.
• An amine can abstract a proton from water, giving an ammonium
ion and a hydroxide ion.
• The equilibrium constant for this reaction is called base-dissociation
constant, symbolized by Kb.
Kb = [RNH3
pKb = - log 10 Kb
Stronger base have smaller values of pKb
• The basicity of the amines depends on the ability of the lone pair
none bonding electrons at nitrogen atom to form bond with an acid.
• The more easier the lone pair electrons formed bond with the acid,
will make the amines a stronger base.
• Factors that effect the basicity of the amines:
i) substitution by alkyl groups
- the presence of alkyl groups (electron-donating group) such as (CH3-)
and (CH3CH2-) will make the amine become more basic.
- for example, methylamine is more basic than ammonia.
ii) substitution by electron-withdrawing groups
- the presence of electron-withdrawing groups or atom will decrease
- for example, nitroaniline is less basic than aniline
Basicity of aromatic amines
* Aromatic amines is less basic than aliphatic amines and
- the lone pair of electrons on the nitrogen atom is delocalised
into the benzene ring.
- As a result, the lone pair of electrons is less available for
donation to an acid.
- The reaction is shifted toward the left and makes aniline a
weaker base than ammonia or aliphatic amines.
• Salt formation
• Reaction with nitrous acid
• Amide formation
• Ring halogenation of phenylamine
REACTIONS OF AMINES
• Reaction of amines and acid will give amine salt.
• Amine salt:
- composed of two types of ions:
i) the protonated amine cation (an ammonium ion)
ii) anion derived from the acid
• Amine salts are ionic, have higher melting points,
nonvolatile solids, more soluble in water than the parent
amines and slightly soluble in nonpolar organic solvents.
• Nitrous acid (HNO2) is unstable and is prepared in situ by the
reaction of dilute HCl or dilute H2SO4 with sodium nitrite in
the absence of heat.
NaNO2 (s) + HCl (aq) → NaCl (aq) + O=N-OH (aq)
• Nitrous acid can be used to differentiate primary, secondary
and tertiary aliphatic amines.
Reaction with nitrous acid
Primary aliphatic amines
• When aliphatic primary amines react with HNO2, nitrogen is evolved
rapidly and an alcohol is produced.
RNH2 + O=N-OH → R-OH + H2O + N2 (g)
• For example, ethylamine gives nitrogen and a mixture of ethanol
(60%), ethene and other products.
C2H5NH2 + O=N-OH → C2H5-OH + H2O + N2 (g) + other products
• The reaction of propylamine with HNO2produces nitrogen and a
mixture of 1-propanol (7%), 2-propanol (32%) and propene (28%).
• The reaction of methylamine with HNO2 produces only a little
methanol, and the main products are methoxymethane and
• Aliphatic secondary amines react with HNO2 at room
temperature to form nitrosoamines / nitrosamines (yellow oils).
R2N-H + HO-N=O → R2N-N=O + H2O
Secondary aliphatic and aromatic amines
• A tertiary aliphatic amines react with HNO2 will produced
ammonium salts which is dissolve readily in water as a clear
R3N + HNO2 → [R3NH]+
NH2 HNO2 HCl N2
RT = room temperature
Tertiary aliphatic amines
Primary aromatic amines
• A primary aromatic amines react with cold HNO2 and
dissolved in dilute HCl at 0-5o
C will produced diazonium
salt. When this cold salts heated at room temperature,
nitrogen gas will evolved.
Tertiary aromatic amines
a nitosoamiline compound (yellow precipitate)
• Tertiary aromatic amines reacts with nitrous acid by
undergoing substitution at the para position of the benzene
ring to form nitrosoaniline which is a yellow precipitate.
i) Reaction with acyl chlorides
• Primary and secondary amines are acylated at room
temperature by acyl chlorides to form N-substituted amides.
RNH2 + CH3COCl → RNHCOCH3 + HCl
R2NH + CH3COCl → R2NCOCH3 + HCl
• Tertiary amines are NOT acylated because they do not have
hydrogen atom attached to the nitrogen atom.
ii) Reaction with acid anhydrides
• Primary and secondary amines are readily acylated
by acid anhydrides to yield the corresponding N-alkyl
or N-aryl amides.
• For example,
• When bromine water is added to phenylamine (aniline) at
room temperature, decolorisation of the bromine water
occurs and a white precipitate of 2,4-6-tribromoaniline
(C6H4Br3N) is obtained.
• This reaction is used as a test for aniline.
Ring halogenation of phenylamine
SYNTHESIS OF NYLON
• General reactions:
• Nylons are condensation copolymers formed by reacting
equal parts of a diamine and a dicarboxylic acids, so that
peptide bonds form at both ends of each monomer in a
process analogous to polypeptides biopolymers.
DiaminesDicarboxylic acids Nylon
USES OF AMINES
Basic concepts of nylon production
• The first approach:
- combining molecules with an acid (COOH) group on each
end are reacted with two chemicals that contain amine (NH2)
groups on each end.
- Form nylon 6,6, made of hexamethylene diamine with six
carbon atoms and acidipic acid, as well as six carbon atoms.
• The second approach:
- a compound has an acid at one end and an amine at the
other and is polymerized to form a chain with repeating units
- Form nylon 6, made from a single six-carbon substance
• Primary aromatic amines are used as a starting material for the
manufacture of azo dyes.
• Azo compounds:
- compounds bearing the functional group R-N=N-R', in which
R and R' can be either aryl or alkyl.
- N=N group is called an azo group
- HNNH is called diimide
• Aryl azo compounds have vivid colors, especially reds,
oranges, and yellows
SYNTHESIS OF DYE
Yellow azo dye
• Amines react with nitric(III) acid to form diazonium salt,
which can undergo coupling reaction to form azo
• Azo-compounds are highly coloured, they are widely
used in dyeing industries, such as:
i) Methyl orange
ii) Direct brown 138
iii)Sunset yellow FCF
• Methyl orange - used as acid-base indicators due to
the different colors of their acid and salt forms
• Artist’s paints – clays, yellow to red range
• Dye in food and textiles
Uses and important of azo dye
E107 : Yellow 2G
E110 : Sunset Yellow
E122 : Azorubine
AZO DYES USED
E123 : Amaranth
E124 : Ponceau 4R
E129 : Allura Red
E151 : Brilliant Black