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AMINESNURUL’ AIN BINTI JAMION
1
ORGANIC CHEMISTRY II CHM301
INTRODUCTION Amines are similar to ammonia (base) with
one or more alkyl groups bonded to the nitrogen atom.
The classification: 1o, 2o, or 3o corresponding to the number of
hydrogen atoms or alkyl replaced. General structure:
NH
H
H Ammonia
NR
H
HN
R
R'
HN
R
R'
R''
2
Identify whether the amino group shown by the arrow is primary, secondary or tertiary.
3
N
Cl
NH
CH3
N
OH
CH3
Hydroxychloroquine
4
NOMENCLATURE OF AMINES
Count the carbons in the longest chain containing the amine
Drop the –e ending for the parent name and add –amine
For a secondary amine an N prefixes the compound giving the shorter carbon chain its side chain prefix name
For a tertiary amine an N,N prefixes the compound giving the two shorter carbon chains their side chain prefix names
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Structural Formula
Condensed Structural Formula
CH3NH2 CH3CH2NHCH3 CH3CH2N(CH3)2
CA format methanamine
N-methylethanamine
N,N-dimethylethanamine
N HC
H
H
H
H
N CH3C
H
C
H
H
H
H
H
N CH3C
CH3
C
H
H
H
H
H
Aromatic amines belong to specific families, which act as parent molecules.
For example, an amino group (—NH2) attached to benzene produces the parent compound aniline.
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NOMENCLATURE OF AMINES
phenylamine
The prefix ‘amino’ is used to indicate the presence of an –NH2 group in a molecule containing more than one functional group.
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NOMENCLATURE OF AMINES
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Compounds with two –NH2 groups are named by adding the suffix ‘diamine’ to the name of the corresponding alkane or aromatic compounds.
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H2N (CH2)6 NH2NH2H2N
hexane-1,6-diamine(1,6-hexanediamine)
benzene-1,4-diamine(1,4-benzenediamine)
NOMENCLATURE OF AMINES
PREPARATION OF AMINES
1. Reduction of nitro compounds2. Reduction of halides with
ammonia3. Reduction of amides4. Reduction of nitriles5. Hoffmann degradation of amides
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1. Reduction of nitro compounds – gives 1o amines Aromatic amines are normally prepared by reduction of
the corresponding aromatic nitro compound. Aniline is prepared from nitrobenzene.
Reducing agents: Fe/H+, Sn/H+ or catalytic hydrogenation (example, H2/Pd or Pt or Ni).
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PREPARATION OF AMINES
Another example:
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PREPARATION OF AMINES
2. Reduction of halides with ammonia The reaction of ammonia with an alkyl halide leads
to the formation of a primary amine.
The primary amine that is formed can also react with the alkyl halide, which leads to a disubstituted amine.(2o amine)
12
PREPARATION OF AMINES
Further reaction can form a trisubstituted amine.(3o amine).
In general:
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PREPARATION OF AMINES
3. Reduction of amides Amides yield primary amines on reduction by lithium aluminum hydride, LiAlH4. The oxygen atom is replaced by two hydrogen atoms. 2o and 3o amides produce 2o and 3o amines, respectively. Reaction occurs via nucleophilic acyl substitution then nucleophilic addition.
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PREPARATION OF AMINES
4. Reduction of nitriles Nitriles can be reduced by strong reducing agent
like H2 with catalyst (example Ni) or LiAlH4 to yield primary amines via nucleophilic addition reaction.
Example:
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PREPARATION OF AMINES
R CN 2H2, catalyst
or LiAlH4, ether R CH2NH2
5. Hoffmann degradation of amides Heating the amides with a mixture of bromine
and KOH or NaOH. amides will change to amines. is used to shorten the chain by one carbon.
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PREPARATION OF AMINES
∆
REACTION OF AMINES
1. Formation of amides2. Amine alkylation: formation of
quarternary salts3. With nitrous acid4. Isocyanides (nitrile compound)5. Benzenediazonium salts
1. Preparation of Benzenediazonium chloride
2. Reaction of Benzenediazonium chloride 17
1. Formation of amidesa. From acyl chlorides
Addition of 1o , 2o (or ammonia) to acid chlorides results in amides.
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REACTION OF AMINES
Example:
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REACTION OF AMINES
1. Formation of amidesa. From acid anhydride
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REACTION OF AMINES
2RNH2 R C
O
NHR
2R2NH R C
O
NR2
R C
O
O C
O
R
R C
O
O C
O
R
R C
O
O RNH3+
R C
O
O R2NH2+
acid anhydride amine amide
1. Formation of amidesa. From ester
Esters reacts with ammonia, primary and secondary amines to produce amides and alcohols.
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REACTION OF AMINES
R C
O
O Rester
N R C
O
NH R OHH
H
R
R
R C
O
O Rester
N R C
O
N R OHH
R
R
R
R
secondary amide
tertiary amide
EXAMPLE
H3C C
O
O CH2CH3 N H3C C
O
NH2 CH3CH2 OH
H
HH0-5OC
primary amine
secondary amine
2. Amine alkylation: formation of quarternary salts
Reaction of amines and acid will give amine salt (an ammonium ion).
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REACTION OF AMINES
CH3CH2NH2 + HCl CH3CH2NH3+ + Cl -
n-propylamine n-propylammonium chloride
NH2CH3CH2CH2 HCl NH3ClCH3CH2CH2
N(CH3CH2)3 HCl
triethylamine triethylammonium chloride
NH Cl(CH3CH2)3
Amine alkylation: formation of quarternary salts Examples:
23
REACTION OF AMINES
n-propylamine n-propylammonium chloride
NH2CH3CH2CH2 HCl NH3ClCH3CH2CH2
N(CH3CH2)3 HCl
triethylamine triethylammonium chloride
NH Cl(CH3CH2)3
3. With nitrous acid Nitrous acid is unstable and must be prepared in the
reaction solution by mixing sodium nitrite with acid.
Primary amines react with nitrous acid to yield a diazonium salt, which is highly unstable and degradates into a carbocation that is capable of reaction with any nucleophile in solution. Therefore, reacting primary amines with nitrous acid leads to a mixture of alcohol, alkenes, and alkyl halides.
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REACTION OF AMINES
With nitrous acid Primary aromatic amines form stable diazonium
salts at zero degrees.
25
REACTION OF AMINES
With nitrous acid Secondary aliphatic and aromatic amines form
nitrosoamine (yellow oils) with nitrous acid.
26
REACTION OF AMINES
With nitrous acid Tertiary amines react with nitrous acid to form N-
nitrosoammonium compounds (ammonium salts).
27
REACTION OF AMINES
Reaction of nitrous acid with aliphatic amines in cold acidic solution can be used to distinguish between primary, secondary and tertiary amines.
RNH2 + HNO2 → N2 gas evolution from a clear solution.
(1° amines)
R2NH + HNO2 → An insoluble yellow oil formed (N-nitrosoamine) (2° amines)
R3N + HNO2 → A clear solution (ammonium salt formation)
(3° amines) 28
REACTION OF AMINES
4. Isocyanides (nitrile compound)• Primary amines heated with trichloromethane
(CHCl3) and alcoholic KOH solution will produce a foul odor of isocyanide, RNC.
• Isocyanide: - an organic compound with functional group
- The CN functionality is connected to the organic fragment via the nitrogen atom, not via carbon atom.
- a zwitterion (nitrogen atom carries positive charge, carbon atom carries negative charge).
29
REACTION OF AMINES
R N C
30
REACTION OF AMINES4. Isocyanides (nitrile compound)
examples:
31
5. Benzenediazonium salts1. Preparation of Benzenediazonium
chlorideStructure• has the formula C6H5N2+Cl¯• a diazonium group is attached to the benzene ring
• the aromatic ring helps stabilise the ion
REACTION OF AMINES
5. Benzenediazonium salts1.Preparation of Benzenediazonium chlorideFrom phenylamine (which can be made by
reduction of nitrobenzene)Reagents: nitrous acid and hydrochloric acidConditions: keep below 10°CEquation:
C6H5NH2 + HNO2 + HCl C6H5N2 + Cl¯+ 2H2O
32
REACTION OF AMINES
33
REACTION OF AMINES5. Benzenediazonium salts
2. Reaction of Benzenediazonium chloride Diazonium salts of aromatic amines are very
useful as intermediates to other compounds. Aromatic diazonium salts are only stable at
very low temperatures (zero degrees and below), warming these salts initiates decomposition into highly reactive cations.
These cations can react with any anion present in solution to form a variety of compounds. Figure illustrates the diversity of the reactions.
34
REACTION OF AMINES5. Benzenediazonium salts
2. Reaction of Benzenediazonium chloride
• The nitrogen gas is released.