ABSTRACT
Furans are volatile, fairly stable compounds with pleasant odours. Furan itself is slightly soluble in water. It is readily available, and its commercial importance is mainly due to its role as the precursor of the very widely used solvent tetrahydrofuran. The aromatic furan ring system, though not found in animal metabolism, occurs widely in secondary plant metabolites, especially in terpenoids: perillene is a simple. Vitamin C, ascorbic acid, is at the oxidation level of a trihydroxyfuran, though it assumes an unsaturated lactone tautomeric form. Furan and its simple alkyl derivatives are decomposed by the usual strong acid reagents, but the pyridine–sulfur trioxide complex can be used, disubstitution of furan being observed even at room temperature. Furan reacts vigorously with chlorine and bromine at room temperature to give polyhalogenated products, but does not react at all with iodine. Carboxylic acid anhydrides or halides normally require the presence of Lewis acid for Friedel-Crafts acylation of furans, though trifluoroacetic anhydride will react alone.
