Table of Contents
Introduction of furan
Furan is an organic compound with the chemical formula C4H4O. It is an extremely volatile and highly flammable compound, and its structure consists of four carbon atoms surrounded by two oxygen atoms. It also has a role in the production of polymers such as polyethylene furanoate (PEF), which is used as a biodegradable plastic packaging material. Additionally, furan-based dyes are used for industrial applications such as paper manufacturing and printing.
Furan is a five membered heterocyclic compound derived from decomposition of substance containing pentose ring & cellulosic solids such as pure wood. Furan & furfuran are the other synonyms used for furan. Its molecular formula is C4H4O and molecular weight is 68g/mol.
Hybridization of furan
The atoms in the pyrrole ring are four carbon atom and one oxygen atom. The oxygen atom consists of three sp3 hybrid orbitals out of which two are used to make bond with carbon by sp2-sp2 hybridization. While the third remains unshared and don’t form any bonding, this orbital remains in the plant of ring but extends away from the main ring.
A pair of electrons is present in the P-orbital, while there is one electron present each in the pz orbital of the carbon atom. The aromaticity of the ring is due to the completion of aromatic sextet. This sextet is completed by 5 p-orbital of oxygen & carbon(4) atoms present in same plane. This causes their overlapping to yield six electrons.
Physical properties of furan
1. It is a colourless liquid.
2. It is only slightly soluble in water.
3. It has a chloroform like smell.
4. Boiling point is 32°C
Synthesis of furan
1. Paal Knorr synthesis (from 1,4-diketo compounds)
In this reaction, acetonylacetone (Hexane-2,5-dione) convert into an end form, which further on dehydration give 2,5-dimethyl furan.
2. From furfural
In this reaction, furfural undergoes decarboxylation (remove co) by heating in a steam at 673K in the presence of silver oxide.
3. Feist binary synthesis
In this reaction, bita-ketoester react with alpha-haloketones in the presence of pyridine to gives derivatives of furan.
4. From furoic acid
Decarboxylation of furoic acid yield furan.
5. From pentose sugar
In this reaction, pentose sugar compound is dehydrated and formed furfural. Which further undergoes decarboxylation and formed furan.
Chemical reactions of furan
In this reaction, furan is treated with mixture of acetic anhydride and nitric acid to give 2-nitrofuran.
In this reaction, furan is treated with pyridine -SO3 complex to give 2-furan sulphonic acid.
3. Friedel craft acylation
Furan on reaction with acetic anhydride in the presence of boron trifluoride gives 2-acetyl furan.
4. Oxidation reaction
In the oxidation reaction, furan gives succinaldehyde via formation of 1,4-peroxide.
Medicinal uses of furan
1. It is used as a solvent for resins.
2. It is used in the production of agricultural chemicals stabilizers & pharmaceuticals.
3. Ascorbic acid is formally a 1,2,3-trihydroxyfuran but assumes a tautomeric lactone form.
4. Drugs are: Ranitidine, Prazosin, Pilocarpine etc.