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Hetero cyclic Analogues of Naphthalene with one heteroatom
(1) (2) (3)
N
Quinoline isoquinoline
N N+
Quinolizinium
The most investigated compound of this group contain a nitrogen atom , and theoretically can be drived from naphthalene by the substation of carbon or carbon and hydrogen atoms by a nitrogen atom .The same result can be obtained by fusing a benzene on to that of pyridine and three structure result .Derivative of all three ring system 1 , 2 , 3 occure naturally in the form of alkaloide
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(4) (5) (6)
O
Benzopyrylium
+
2H -Benzopyrylium
O O
4H -Benzopyrylium
These three type of compound are essentially aromatic in character .The oxygen analogues of naphthalene which will be considered here are those
derived from benzopyrylium cation (4) and benzopyranes (5) and (6) derivatives of these systems occure widely in plants and the
anthocyanins. subistituted benzopyrylium salt are responsible for most red and blue flower coloure .very few sulphur analogues are known and at
present they are not of general interest .
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Physical properties and structure
CHO
NH2
+ |CHO
CH3 NaOH
N
H2O2
NHOOC
HOOC
or KMnO4
)1( )2(
O3
N
3
O3
O
|CHO
CHO
NOHC
OHC
+
diozonide glyoxal pyridine 2,3 - dicarbaldehyde
2 - amino benzaldehyde
Quinoline is a colourless liquid its b.p 237cº it's miscible with most organic solvent ,its useful high – boiling solvent for many types of organic compound .The structure for quinoline was first proposed by korner ,and was supported at an early stage by an oxidation to
quinolinic acid (2) and by several syntheses of which Friedlander's is shown .
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ozone attacke quinoline at the 5,6 and 7,8 position the initial product is a diozonide , decomposition of diozonide give pyridine 2,3 – dicarbaldehyde and glyoxal
1
345
6
78
N 2
The resonance energy of quinoline (47.3) kcal/ mol calculated from heat of combustion data the position of quinoline ring are
usually numbered as structure .
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Chemical reaction
1 – basicity Quinoline is a slightly weaker base than pyridine and form many salt which sparingly soluble in water .
N N
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Quinoline is a colourless liquid , it form 1 – oxide with hydrogen peroxide and acetic acid and quaternary
salt with methyl iodide which with alkali give the hydroxide these are in equilibrium with the corresponding bases (3) which can be
tautomerize to an open – chain (4) the oxidation of (3)give (5) .
Addition and ring – opening reactions :
H2O2 / ACOH
N NO
+
-
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N
MeI
N+ I-
Me(1)
Na+ OH-
HIMe
+N
(2)
OH-
(3)(5)
N
H
OHMe
+-[O]
N O
H+ OH-
N
H
OHH
MeOH
(4)
ONHMe
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NMe
2
+ OH-Na/Hg
Emde's
methodsNMe
2
3 - phenyl - N - dimethyl-
Propane amine
N
O H
H
H
H
Me2
-H 2 O
Me2
N
Me
N
+MeOH
O - propene - N - dimethylaniline
160
15 mm
ordinary
pressure
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Reduction :
1,2,3,4-tetrahydroquinoline
N
tin / HCl
NH
H2O
Quinoline is easily reduced to tetrahydroquinoline by tin and hydrochloric acid or by hydrogenation .
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Oxidation :
Oxidation of quinoline opens the ring giving quinolinic acid (1) the 2 – phenyl quinoline (2) and hydroxide (3) the nitrogen – containing ring can be split
N
KMnO4
N
HOOC
HOOC
(1)
(2)
N
COOH
NHCOPh
KMnO4
N Ph
N OH
H
R
KMnO4
N
COOH
NCHOR
(3)
N - alkyl - 2 hydroxy quinoline
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N N=C - Ph
OH
H
OH
KMnO4
N Ph
OH
OHN N - C - Ph
C = O
O
H H
H
H
[O]
COOH
N - C - PhH O
-CO2CH3
N - C - PhH O
[O]COOH
N - C - PhH O
(enol form ) ( keto form )
Mechanism
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Substitution reaction
The nitrogen atom deactivates the pyridine ring and so the subistituent enter the benzene ring .calculation of charge densities show that position 8 will be attack by electrophilic reagent and position -2- by nucleophilic reagents .In practice nitration and sulphonation give a mixture of – 5 and 8 – substituted product . In bromination the heterocyclic rings is subistituted in the 3 – position .
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N..
+
-
+
N....
N-
N..
N..
+
Quinoline resonance hybrid indicate the same result for electrophilic and nucleophilic substituent .
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N
fuming HNO 3
fuming H 2SO4N
NO2
NNO2
+
5 - nitroquinoline 8 - nitroquinoline
N 220 c0
fuming H 2SO4
quinoline - 8-sulphonic acid
quinoline - 5-sulphonic acid
+N
SO3HN
SO3H
Electrophilic subistitution
NAgSO4
Br2 H2SO4
5 - bromo-quinoline
+N
Br N
Br
8 - bromo-quinoline
Br2 CCl4 /pyridine N
Br
3 - bromo-quinoline
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N
NaNH2 lig NH 3 +
N NH2N
NH2
2 - amino-quinoline
KOH 220 c0 4 - hydroxy-
quinoline N
OH
N OH +
Nucleophilic subistitution
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Synthesis of quinoline
1 – Skraup's synthesis
H2SO4 C6H5NO2
NNH2
+
CH2OH|CH - OH|CH2OH
+ C6H5NH2 + H2O
It is the most useful method for preparing quinoline from aniline and glycerol in presence of concentrated sulphuric and nitrobenzene .
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The following steps seem to be involved
CH2 - CH - CH2 | | |OH OH OH
H2SO4 -2H2O
CH2 ||CH |C = O |H
CH2 |CH |C - O - |H
+
1 – Dehydration of glycerol by hot sulphuric yield the unsaturated aldehyde acroline .
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NH
H
+H
C
O
CH ||CH2 N
CH2
H
CH2
C
O
H
β ( phenylamino) propionaldehyde
2 – Nucleophilic addition of aniline to acrolein to yield β – (phenylamino) – propionaldehyde .
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NCH2
H
CH2
C
O
HH+
NCH2
H
H
CH2
C
OHH+
NH
OHHH
-H2O
NH
1,2 - dihydroquinoline
3 – Electrophilic attacke on the aromatic ring by the electron deficient carbonyl carbon of the protonated aldehyde .
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NH
+ C6H5NO2H+
N+ C6H5NH2 + H2O
4 – Oxidation by nitrobenzene resulting in the aromatization of the new formed ring