Preparation and Reactions of Thiophene

Preparations and Reactions of Thiophene

Thiophene is a sulfur containing five-membered planar heterocyclic compound with the formula C₄H₄S. it is aromatic as indicated by its extensive substitution reactions. It is a colorless liquid with a benzene-like odor. In most of its reactions, it resembles benzene.

Preparation of Thiophene

Preparation of Thiophene from Acetylene

By passing a mixture of acetylene and H₂S through a tube containing aluminium oxide at 400°C, Thiophene is obtained.

Preparation of Thiophene from Furoic Acid

Thiophene is obtained when furoic acid is distilled with barium sulphide.

Preparation of Thiophene from n-Butane (Commercial Method)

When sulphur reacts with n-butane in gas phase at 650°C, Thiophene is obtained.

Preparation of Thiophene from Sodium Succinate

When sodium succinate is heated with phosphorous trisulphide, Thiophene is obtained.

Physical Properties of Thiophene

Thiophene is a colorless liquid, Boiling Point is 84° C, Insoluble in water but miscible with most organic solvents. Its odour is similiar to benzene.

Chemical Properties of Thiophene/Reactions of Thiophene

Resonance of Thiophene

Resonance energy of thiophene is 117 KJ/mol. Thiophene is a resonance hybrid, the S atom contributing two electrons to form a (4n+2)π electron. Sulphur is less electronegative than oxygen or nitrogen and can also use 3d orbitals (oxygen and nitrogen cannot). Hence more canonical forms are possible for thiophene than for furan and pyrrole.

Basic Character of Thiophene

Thiophene does not show any basic properties. It is much more stable to acids than either pyrrole and furan.

Electrophylic Substitution Reactions

Thiophene undergoes electrophylic substitution reactions at carbon-2 and gives 2-substituted product however gives 3-substituted product only when both the 2nd position (i.e.Carbon-2) are already occupied.

Nitration of Thiophene

Thiophene is nitrated by solution of nitric acid in acetic anhydride to give 2-nitrothiophene.

Sulphonation of Thiophene

Thiophene is sulphonated with concentrated sulphuric acid to give thiophene-2-sulphonic acid.

Halogenation of Thiophene

Thiophene reacts vigorously with chlorine and bromine at room temperature to give polyhalogenated thiophene. For monohalogenated thiophene, much milder conditions to be used.

Friedel-Craft Acylation of Thiophene

Thiophene is acetylated with acetic anhydride in the presence of phosphoric acid to give 2-acetylpyrrole.

Mercuration of Thiophene

Thiophene undergoes mercuration with mercuric chloride in aqueous sodium acetate to produce 2-chloromercurithiophene.

Chloromethylation of Thiophene

Thiophene racts with formaldehyde and HCl to give 2-chloromethylthiophene.

Reduction of Thiophene

Thiophene reduced under different conditions to give different products.

Reaction of Thiophene with n-Butyl Lithium

Thiophene reacts with n-butyllithium to yield 2-lithium thiophene which when reacts with carbondioxide in HCl gives thiophene-2-carboxylic acid.

Preparation and Reactions of Pyrrole

Preparation and Reactions of Furan