The document outlines the synthesis, reactions, and medicinal uses of furan, a heterocyclic compound. It details various synthesis methods including those from mucic acid, furfural, and furoic acid, and describes characteristic reactions such as electrophilic substitutions and oxidation. Additionally, it lists medicinal applications of furan derivatives such as furazolidone, nitrofurazone, nitrofurantoin, ranitidine, and furosemide.

1. Heterocyclic Compounds
Furan
Synthesis,Reactions&MedicinalUses
Prof.Dr.P.Venkatesh
Jagan’s Institute of Pharmaceutical Sciences - Nellore
Chem Eazy
O

2. Synthesis of Furan
1. Synthesis from Mucic acid
Furan may be prepared from mucic acid which gives furoic acid on dry
distillation.
Furoic acid on decarboxylation at its boiling point gives furan.
O H
O H
o h
OH
OH
OH
COOH
HOOC
HO
Mucic acid
Dry distiiled
- 3H2O, - CO2
O COOH

- CO2
O
Furoic acid Furan
Chem Eazy

3. 2. Synthesis from Furfural
Furfural on oxidation with potassium dichromate gives furoic acid which on
subsequent decarboxylation at 200 - 300°C yields furan.
By decarboxylation of furfural in steam in the presence of silver oxide catalyst.
O CHO
[O]
K2Cr2O7/H+
O COOH
2-furoic acid
Furfural

- CO2 O
Furan
O CHO
Furfural
Ag2O
- CO O
Furan
Chem Eazy

4. 3. Synthesis from Furoic acid
By the decarboxylation of furoic acid in quinoline in the presence of copper
powder
O COOH
2-furoic acid
O
Furan
- CO2
Chem Eazy

5. Characteristic Reactions of
Furan
Chem Eazy

6. 1. Electrophilic substitution
Furan, like pyrrole, undergoes electrophilic substitution reactions mainly at 2-
positions.
Substitution at 3-position occurs only when both of the 2-positions (2&5) are already
blocked.
2
3
O
1
5
4
Chem Eazy

7. i) Nitration: Nitrated with hot solution of nitric acid in acetic anhydride
ii) Sulphonation: Sulphonated by sulphur trioxide in pyridine at 70°C
O
+ SO3
Furan
C5H5N
70 °C O SO3H
Furan - 2- sulphonic acid
O
+ HNO 3 + (CH3CO) 2O
O NO2
+ 2CH3COOH
Furan Nitric acid Acetic anhydride
2 -nitrofuran
Acetic acid
Chem Eazy

8. iii) Halogenation: At room temperature furan reacts extremely rapidly with
halogens and the liberated halogen acids cause polymerisation.
Hence halogenofurans are generally prepared by indirect methods.
O COOH
Br2
O COOH
Br

- CO2
O
Br
Furoic acid
5 -bromo- 2- furoic acid 2 -bromofuran
O
Furan
HgCl2
CH3COONa O HgCl
I2
O I
Furylmercury chloride 2 -iodofuran
Chem Eazy

9. However, chlorination of furan at 40°C gives 2-chloro and 2,5-dichloro
products.
Action of bromine in dioxan at 0°C on furan produces 2-bromofuran.
O
Furan
Cl2
40 °C O Cl
+
O Cl
Cl
2 -chlorofuran 2, 5 -chlorofuran
O
Furan
Br2/Dioxan
0 °C O Br
2 - bromofuran
Chem Eazy

10. iv) Acylation [Friedel-Craft’s reaction]:
Reaction of furan with acetic anhydride in the presence of boron trifluoride at 0°C
undergoes acylation.
v) Mercuration:
Furan on reaction with mercuric chloride in sodium acetate gives 2-furylmercury
chloride.
O
Furan
+ (CH3CO) 2O
Acetic anhydride
O COCH 3
+ CH3COOH
2 -acetylfuran
BF3
0 °C
O
Furan
O HgCl
HgCl2
CH3COONa
2 -furylmercury chloride
Chem Eazy

11. vi) Formylation:
Gattermann reaction: Formylated by a mixture of hydrogen cyanide &
hydrogen chloride in the presence of Lewis acid catalyst.
Vilsmeier reaction: Undergoes Vilsmeier reaction with DMF and
Phosphorus oxychloride
O
Furan
HCN - HCl
H2O O CHO
Furfural
O
Furan
O CHO
Furfural
(CH3)2NCHO - POCl3
Chem Eazy

12. 2. Reaction with diazonium salts
Gomberg Reaction: Furan on treatment with diazonium salts in alkaline
solution gives arylfurans.
3. Reaction with maleic anhydride
Diel’s-Alder reaction: Furan acts as a diene towards strong dienophiles.
O
Furan
+ C6H5N2Cl
O C6H5
+ N2 + HCl
2 -phenylfuran
O
Furan
+
O O
O
Maleic anhydride
(diene) (dienophile) O O
O
O
Furan-maleic anhydride adduct
Chem Eazy

13. 4. Reaction with alkyl or aryl lithium
Furan reacts with alkyl lithium to form 2-lithium derivative from which
alkyl furan & furoic acid can be prepared.
O
+ CH3CH2CH2CH2Li
n-Butyllithium
Furan
O Li
2 -Lithiofuran
O R
2 -alkylfuran
i) RX
ii) H+
i) CO 2 ii) H
+
O COOH
Furoic acid
Chem Eazy

14. 5. Oxidation: Furan is completely oxidised by most of the oxidising agents. It is
polymerised to resinous product even by air via peroxide.
6. Reduction: Furan is catalytically reduced over Raney nickel or palladium-
palladium oxide to form tetrahydrofuran (THF).
O
Furan
O2
O
O O
H2
O
O
Succindialdehyde
O
Furan
Ni/H2
Pd - PdO/H2 O
THF
Chem Eazy

15. Medicinal Uses of Furan
Chem Eazy
O

16. Furazolidone
Furazolidone is used for the specific and symptomatic treatment of bacterial or
protozoal diarrhoea and enteritis caused by susceptible organisms.
O
O2N CH N N
O
O
Furazolidone
Chem Eazy

17. Nitrofurazone
It is a topical anti-infective agent effective against gram-negative and gram-
positive bacteria. It’s used for superficial wound & injuries and skin infections.
O
O2N CH N NH NH2
C
O
Nitrofurazone
Chem Eazy

18. Nitrofurantoin
Nitrofurantoin is indicated to treat acute uncomplicated urinary tract
infections.
O
O2N CH N N
NH
O
O
Nitrofurantoin
Chem Eazy

19. Ranitidine
Ranitidine is a histamine H2 receptor antagonist used to treat duodenal ulcers,
gastric ulcer, gastroesophageal reflux disease (GERD) and erosive esophagitis.
O
H2C CH2-S-CH2-CH2-NH-C-NH-CH 3
N
H3C
CH3
CH-NO 2
Ranitidine
Chem Eazy

20. Furosemide
Furosemide is a loop diuretic used to treat hypertension and edema in
congestive heart failure, liver cirrhosis, renal disease and hypertension.
O CH2
NH SO2NH2
Cl
HOOC
Furosemide
Chem Eazy