1
Heterocyclic Compounds
3rd Year Students Special Chem, Chem-Phys, Geo-chem, Zoo-Chem, Bot-Chem,
Synthesis Of Furan
2
1. From cyclodehydration of 1, 4-diketones by acidic reagents, e.g., H2SO4, ZnCl2, Ac2O and P2O3
O H3CH3CEtOOC
C
COHH3C
CC
OH
CH3
COOEtH2SO4
EtOOCHC
C
O
CH3
HCC
O
CH3
COOEt2CH3COCH2COOEt + 2C2H5ONa
Na+
I2CH3COCHCOOEt
2. From knorr-pyrrole synthesis
Synthesis Of Furan
3
3. Feist’s synthesis
O CH3
H3CH3C C
CH2Cl
O C
CH Cl
H3C OH HC COOEt
C CH3
OH
E.A.A
Chloroacetone
4. From decarboxylation of furoic acid.
O COOHO
+ CO2
Synthesis Of Furan
4
5. Furfural (furan 2-carboxaldehyde)
O
HO OH
CHO
OHOH
CHO
OHOHCHO
Furfural is commercially obtained from pentose (occurred in oat hulls) by stream distillation
6. By treatment of α-hydroxyketones and acetylenic compounds
O
OH
R
CO2CH3
CO2CH3
O CO2CH3
CO2CH3RK2CO3 H+
-H2O
R
H2COH
C
C
CO2CH3
CO2CH3
C=O
Synthesis Of Pyrrole
5
Reactions Of Furan
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1. Ring opening of furan:
The mildest acidic conditions required to affect the hydrolysis of furan into succinaldehyde to prevent the polymerization
O OH
H+ H2O
OHC CHO
2. Addition reactions of furuan:
a) Reduction:
O O
+ H2
THF
Reactions Of Furan
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b) Diels-Alder reaction:
O O
HC
CH
OO
O
O
+
O
O
c) Addition of carbenes (with diazomethane):
O O
CH2N2
-N2
Reactions Of Furan
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d) Furanis not stable in presence of air and usually stabilized by addition of small amount of hydroquinone. Air oxidation takes place by 2, 5 addition forming peroxide. Hydrogenation of furan peroxide gives succinaldehyde.
O O
O2O O
[H] H2C
OHC
CH2
CHO
3. Electrophilic substitution of furan:
*Furan cannot be directly nitrated with nitric acid (is very readily attack by oxidizing agents). 2-Nitrofuran may be prepared by nitrating furan with acetyl nitrate (CH3COONO2). Similarly, furan cannot be directly sulphonated, but 2-sulphonic acid may be prepared by action of SO3/pyridine on furan. *If (-I) group is present in the ring, then sulphonation can be carried out directly, e.g., furoic acid gives furoic 5-sulphonic acid. *Furan reacts readily with halogen, but the liberated (HX) causes polymerization, because of this halogenated furan prepared by indirect method, e.g., by brominating furoic acid and decarboxylating the product, 5-bromofuroic acid to 2-bromofuran by heating in quinolone in the presence of copper bronze. Aluminum chloride attacks furan ring, and Friedel-Crafts is best carried with SnCl4.
Reactions Of Furan
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O
NH
O
O
O
O O
SO3H
COR
HgOAc Br
HO(CH2)4OH
+
H2O/H+
Br2
2-Bromofuran
TetramethyleneglycolTetrahydrofuran
2,5-dinitrofuran2-nitrofuran
2-acylfuran
furan-2-sulphonic acid
Furan
NH3/Al2O3
450°C
SO3/pyridine
RCOCI/SnCl2
CH3COONO2
0°C
H2/Ni
Hg(OAC)2
O NO2O NO2
O2N
O Li O COOH
C4H9Li 1-CO2
2-HCl
HCl/HCN
O CHO
Synthesis Of Furfural
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1. From dehydration of aldopentoses
HCl
OCHO
CH2OH-(CHOH)3-CHO
CHO
OHH
HHO
OHH
CH2OH
- H2O
CHO
C OH
C H
OHH
CH2OH
CHO
C O
HC H
OHH
CH2OH
CHO
C O
C
CH
CH2OH
H
H
H
CHO
OH - H2O
CHO
Synthesis Of Furfural
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2. From Gattermann’s reaction:
OO
+ HCl/HCN
OCHO
+ H2OCH=NH2
O
+ HCl + H-CN
H-C=NH
ClO
CH=NH
H2O
OCHO
Reactions Of Furfural
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Furfural is chemically very similar to benzaldehyde as the following
1. It undergoes oxidation (KMnO4) to furoic acid.
2. When it was submitted to react with sodium hydroxide it undergoes cannizzaro reaction
and gives a mixture from furfuryl alcohol and sodium salt of furoic acid.
3. It under goes benzoin condensation and gives furoin.
4. It reacts with aniline in the presence of acetic acid and gives Schiff’s base.
NH2
aniline
O
O
furfural
+2Ph-NHCH=CH-CH
C
HO
NPhSchiff 's baseBrilliant red
Reactions Of Furfural
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5. It reacts with acetone and yields furfurylidene acetone.
O
O
furfurylidene acetone
6. It reacts with CaO/400ºC, it loses carbon monoxide and gives furan by steam decomposition.
7. With ammonia and ammonium chloride gives 3-hydroxypyridine.
NH3/NH4Cl
H2NO
C
O
H OH
CHO
Reactions Of Furfural
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furfuryl alcohol
tetrahydrofurfuryl alcoholfurfural
H2/CuO
H2/Ni
furfuryl alcohol
(cannizzaroreaction)
+
furoic acid
furoic acid
OCHO
O CH2OH
O CH2OH
O CH2OH O COOH
O COOH
KMnO4
NaOH
Reactions Of Furfural
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furylacrylic acidfurfural
AC2O/AcONa
Alc./KCN
(perkinreaction)
(benzoincondensation) furoin
furil
2
furilic acid
OCHO
O CH CH COOH
O OCH
O OH
O O
O O
O
OH
COOH
OXID
NaOH
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