Chemistry
of Thiophene
Session Objectives
By the end of this
session, students will be able to:
• Discuss the chemistry, reactivity of Thiophene
• Discuss the methods of synthesis and properties of
Thiophene
Chemistry of Thiophene
• Discovered by Victor Meyer in 1882 during his ingenious
experiments on investigation of aromatic compounds
• Occurs in coal tar and large number of thiophene
derivatives occurs in plants and animal metabolism
• Responds to indophenine test- treatment of 1ml of dilute
solution thiophene in benzene with a few mg of isatin and 1ml of conc. Sulfuric
acid gives intense blue color
• Reduced thiophenes are given trivial names
Physical properties of Thiophene:
• Colorless liquid with boiling point of 80 0C and
freezing point -38.3 0C
• Miscible with water but soluble in most organic solvents
Molecular properties of Thiophene:
• Resonance hybrids of thiophene
• Sulfur atom is less electronegative than oxygen and
nitrogen
• Thiophene is greater aromatic and planar molecule with sp2
hybridized carbon atoms
• Electrophilic attack takes place preferably at 2nd
and 5th positions
• Pyrrole is weak base while furan is extremely weak and
thiophene in contrast, seems to be devoid of basic properties
Synthetic methods of Thiophene:
1) From sodium
succinate: classical method by heating a mixture of sodium succinate and
phosphorus trisulfide
2) Ring
closure methods- from unsaturated compounds:
• Involves the use of methyl thioglycolate and its
condensation with dimethyl fumarate in the presence of a base
• From unsaturated compounds:
Chemical properties of Thiophene:
• Contains a sulfur atom which belongs to second row
elements of periodic table
• Can expand its valence shell by using empty d-orbitals in
hybridization
• One of the reason for extreme stability of thiophene-
resembles to benzene in physical and chemical properties
1) Reaction
with acids: very stable to action of acids, very strong acids may bring
about oligomerization
• Orthophosphoric acid under milder conditions has been
found to give trimer
2) Electrophilic
substitution: more reactive than furan and pyrrole
• Preferential attack takes place at 2nd position
A) Halogenation:
with chlorine yields a mixture of substituted products
• Bromination occurs rapidly even in dark at -30 0C
and gives exclusive product
• Iodination results in mono and diiodothiophenes
B) Sulfonation:
• With 95% H2SO4 gives
thiophene-2-sulfonic acid readily
• But chlorosulfonation gives very lower yield of product
C) Friedel-Crafts
reaction:
• Acetylation can be carried out in wide variety of
conditions
• With acetyl chloride in the presence of stannic chloride,
thiophene yields 2-acetylthiophene
• Also reacts with phthalic anhydride in the presence of
aluminium chloride to yield 2,2’-thienoylbenzoic acid
D) Vilsemeier
formylation:
• Formylation proceeds rapidly on thiophene with DMF and
POCl3
Summary
• Sulfur atom is less electronegative than oxygen and
nitrogen
• Thiophene is greater aromatic and planar molecule with sp2
hybridized carbon atoms
• Electrophilic attack takes place preferably at 2nd and 5th
positions