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Pyrrole
dis
Preaperation
1- from succinimide
O
N
H
O
HO
zn
N
H
N
H
OH
2 – From 1,4 – Dicarbonyl compound
H
HO
+ RNH2
H
R
HO
R
1
CH3
NH O
Ketoform
R
N
|
R
subs - pyrrole
+ CH3NH2
O O
R
R
enol form
CH3
R
-H2O
NH
OH R
R
R
O O
CH3
N
|
CH3
CH3
1,2,5 - Trimethylpyrrole
4lec
R
3 – From α-aminocarbonyl compounds
knorr synthesis
condensation of an α – amino – ketone with a ketone possessing a
reactive methylene group α- amino ketone prepared by reducing the
corresponding oximino compound with zinc
CH3 - C = O
|
EtOOC - CH2
CH3 - C = O
|
EtOOC - C = NOH
HNO2
-H2O
CH3 - C = O
|
EtOOC - CH - NH2
H2
CH3 - C - OH
CH2-Cl
+
||
EtOOC - C - NH2
CH3 - C = O
CH - Cl
||
CH3 - C - OH
CH3 - C - OH
||
EtOOC - C - NH2
2
+
CH - Cl
||
CH3 - C - OH
-H2O
CH3 - C
4lecEtOOC
C - Cl
N
H
CH3
Chemical properties
Pyrrole is a weaker base than pyrrolideine
..
N
H
..
N
H
This is because of
1 – Resonance of π electrons
2 – Type of hybrid orbitals of nitrogen atom
The pair of electron in pyrrole occupies an sp2 orbital while in
pyrrolideine occupies sp3orbital and as we know the electron
occupies an sp2orbital is held more tightly and is less available
for sharing with acid than the pair of electrons which occupies
sp3orbital.
3
4lec
Electrophilic subistitution :The reaction takes place predominantly at the α – position we could account for
this orientation of the following basis : the controlling step is the attachment of
the electrophilic reagent which takes place in such a way as to yield the most
stable intermediate carbonium ion
Attack at position 3 yields carbonium ion that is a hybrid of structure I and II .
Attack at position 2 yields a carbonium ion that is a hybrid not only of structure
III and IV ( analogous ) to (I and II ) but also of structure V ; the extra
stabilization conferred by V makes this ion the more stable one
4
4lec
E
E
3
+
H
..
N
N
H
+
H
II
I
+
Y
+
N +
H
- = 2 attack
- = 3 attack
+
2
+
N
H H
E
..
N
H H
III
+
E
IV
More stable ion
5
4lec
+
..
N
H H
V
E
Br
Br2
+
N
H
N
H
HNO3
+
Br
N
H
More stable
NO2
+
N
H
6
NO2
4lec
+
N
H
Furan
Synthesis
1 – Feist Benary synthesis
Treating α – chloroketone with ethyl acetoacetate
CH3 - C = O
|
CH2Cl
EtOOC- CH2
|
+
C=O
EtOOC- CH
||
C - OH
CH3
CH3
CH3 - C - OH
||
CH - Cl
+
HO
CH - OOCEt
||
CH - CH 3
CH3 - C
HC
-HCl
-H2O
Pyridine
C -OOCEt
O
C - CH3
2,4 - di methyl-3-ethylcarbonyl furan
7
4lec
2 – From 1,4 dicarbonyl compound
R
O
O
R'
HO
3-
R
OH HO
P2O5
-H2O
R'
O
OH
H
+ 3H2O
dry
H
distilation HOOC
HO
HOOC
COOH
O
COOH
HO
mucic acid
4–
Ag2O
O
CHO
O
COOH -CO2
Furfural
8
R
4lec
O
R'
5 - Reaction
SO3
1 – Sulphonation
Pyridine
O
SO3H
O
Furan - 2 - Sulphonic acid
Furan decomposed by the usual strong reagent but the pyridine sulphur
trioxide compound under mild condition react with furan to give 2 –
sulphonic acid
2 – Halogenation
Furan react vigorously with chlorine and bromine at room temperature
Cl
O
Cl
2,5 - dichloro furan
9
dioxan
Cl2
+
O
Cl
Br
Br2
O
O
2 - Bromo furan
2 - Chloro furan
4lec
3 – Acylation
Carboxylic anhydrides or carbonyl halides normally react only
in presence of Friedel – Crafts or orthophosphoric acid
all electrophilic subistitution in furan take placte at position 2
and 3 but 2 is more stable for the same reason as pyrrole .
CH3
CH3
AC2O
O
CH3
+
H3PO4
O
COCH3
CH3CO
2 - acetyl -3-methyl furan
10
4lec
O