Oxygen-containing furan-ring derivatives

Furfural (1), derived from annually renewable agricultural byproducts, is an important industrial chemical manufactured and used throughout the world. It is the feedstock for a number of derivative chemicals generically known as furans -the structural characteristic of which is the five-membered oxygen-containing heterocyclic ring. Furfuryl alcohol (2) is the most important derivative of commerce, where it is used primarily in synthesis of adhesive polymers. 

A,B-Diheteropentalenes have only limited solubility in water. The hydrogen donor properties of the NH site of pyrrole and the hydrogen acceptor property of the oxygen atom of the furan ring can increase the solubility of the compounds containing these heteroatoms relative to the systems with only sulfur or selenium atoms in their structure. Alkylation at the nitrogen of furo[3,2-6]pyrrole derivatives increases the solubility in ethanol and other organic solvents. 

Furopyridine derivatives contain a nitrogen atom in a six-membered pyridine ring and an oxygen atom in a five-membered furan ring. Table 2 lists the six parent furopyridine isomers, (14)-(19), with their registry numbers. In this series, compounds (14)- 17) are the most widely investigated isomers. 

The IR data, as discussed above, and the molecular formulas for the first homologs in at least the less-negative Z(O) series in Table IV, indicate that furans dominate the oxygen-containing compounds in both the oil and asphaltene neutral fractions. Furthermore, comparison of the Z(H) and Z(O) values in Tables III and IV, respectively, suggests that the furans are phenomenologically derived from the aromatic hydrocarbons by replacement of ring CH2 by O. 

Furan is the five-membered ring heterocycle containing one oxygen. Thiophene is the five-membered ring heterocycle containing one sulfur. Pyran and thiopyran are the six-membered ring derivatives. 

Figure 9.7 Six- and five-membered cyclic ethers. The stable ring structures which are adopted by hexoses and pentoses are five- or six-membered and contain an oxygen atom. They are named as derivatives of furan or pyran, which are the simplest organic compounds with similar ring structures, e.g. glucofuranose or glucopyranose for five-or six-membered ring structures of glucose respectively.

The common anomers have either a five- or a six-membered ring that contains an oxygen atom. A six-membered ring is a derivative of pyran therefore, the monosaccharide is a pyranose. A five-membered ring is a derivative of furan. 

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