Indole is an aromatic heterocyclic compound, notable for its structure combining a benzene ring and a pyrrole ring, with a formula of C8H7N. Its significance rose from its role as a precursor to important substances like serotonin and tryptophan, with its chemistry evolving from the study of indigo dye. Indole has unique physical and chemical properties, including an intense odor at high concentrations and various medicinal applications through its alkaloid derivatives.

1. Fused Heterocyclic compound-Indole
Lecture by
S.Mathivanan., M.Pharm
Assistant professor
Pharmacy

2.  Indole is an aromatic heterocyclic organic compound with
formula C8H7N.
 It has a bicyclic structure, consisting of a six-membered
benzene ring fused to a five-membered pyrrole ring.
 The name indole is a portmanteau of the words indigo and
oleum, since indole was first isolated by treatment of the
indigo dye with oleum.
Other names
2,3-Benzopyrrole,
ketole,
1-benzazole
IUPAC : 1H-Indole

3. The amino acid tryptophan is an indole derivative and the
precursor of the neurotransmitter serotonin.
Tryptophan
Seratonin

4. Indole chemistry began to develop with the study of the dye indigo.
Indigo can be converted to isatin and then to oxindole. Then, in
1866, Adolf von Baeyer reduced oxindole to indole using zinc dust. In
1869, he proposed a formula for indole .
Certain indole derivatives were important dyestuffs until the end of the
19th century. In the 1930s, interest in indole intensified when it became
known that the indole substituent is present in many important alkaloids
(e.g., tryptophan and auxins), and it remains an active area of research
today
Indigo dye Baeyer’s Indole formula

5. Physical properties
• Indole is a solid at room temperature.
• It occurs naturally in human feces and has an intense
fecal odor.
• At very low concentrations, however, it has a flowery
smell, and is a constituent of many perfumes.
• It also occurs in coal tar.
• The corresponding substituent is called indolyl.
• Density : 1.1747 g/cm3
• Melting point : 52 to 54 °C
• Boiling point253 to 254 °C

6. 1. Aromatic
Chemical Properties
• Unlike most amines, indole is not basic: just like pyrrole, the aromatic character of
the ring means that the lone pair of electrons on the nitrogen atom is not available
for protonation.
• Strong acids such as hydrochloric acid can, however, protonate
indole.
• Indole is primarily protonated at the C3, rather than N1, owing to the
enamine-like reactivity of the portion of the molecule located outside of the
benzene ring. The protonated form has a pKa of −3.6.

7. Synthesis
1. Fischer indole synthesis

8. Synthesis
1. Fischer indole synthesis
Mechanism

9. Synthesis
1. Fischer indole synthesis
Mechanism

10. Synthesis
1. Fischer indole synthesis

11. Synthesis
2. Bischler–Möhlau indole synthesis

12. Synthesis
3. Madelung synthesis

13. Synthesis
3. Madelung synthesis
E.g.

14. Reactions
1. Electrophilic addition to N

15. Reactions
2. Electrophilic aromatic substitution

16. Reactions
2. Electrophilic aromatic substitution

17. Reactions
2. Electrophilic aromatic substitution

18. Reactions
2. Electrophilic aromatic substitution

19. Reactions
2. Electrophilic aromatic substitution

20. Reactions
3. Reduction reactions

21. Reactions
4. Nucleophilic substitution

22. Medicinal uses
(1) Indole alkaloids :

23. Medicinal uses

24. Medicinal uses

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