FURFURANE, or Furane, C4H4O, a colourless liquid boiling at 32° C., found in the distillation products of pine wood. It was first synthetically prepared by H. Limpricht (Ann., 1873, 165, p. 281) by distilling barium mucate with soda lime, pyromucic acid C4H3O·CO2H being formed, which, on further loss of carbon dioxide, yielded furfurane. A. Henniger (Ann. chim. phys., 1886 [2], 7, p. 220), by distilling erthyrite with formic acid, obtained a dihydrofurfurane
which, on treatment with phosphorus pentachloride, yielded furfurane. Furfurane is insoluble in water and possesses a characteristic smell. It does not react with sodium or with phenylhydrazine, but yields dye-stuffs with isatin and phenanthrenequinone. It reacts violently with hydrochloric acid, producing a brown amorphous substance. Methyl and phenyl derivatives have been prepared by C. Paal (Ber., 1884, 17, p. 915). Paal prepared acetonyl acetophenone by condensing sodium acetoacetate with phenacylbromide, and this substance on dehydration yields αα′-phenylmethylfurfurane, the acetonyl acetophenone probably reacting in the tautomeric “enolic” form,
| CH3·CO·CHNa·COOR + C6H5·CO·CH2Br = CH3·CO·CH(CH2COC6H5)·COOR. |
This ester readily hydrolyses, and the acid formed yields acetonyl acetophenone (by loss of carbon dioxide), which then on dehydration yields the furfurane derivative, thus
CH3·C |
CH—CH |  C·C6H5 = H2O+CH3·C |
CH—CH | C·C6H5,
|
| OH HO | ___O___ |
L. Knorr (Ber., 1889, 22, p. 158) obtained diacetosuccinic ester by condensing sodium acetoacetate with iodine, and by dehydrating the ester he prepared αα′-dimethylfurfurane ββ′-dicarboxylic acid (carbopyrotritaric acid), which on distillation yields αα′-dimethylfurfurane as a liquid boiling at 94° C. Paal also obtained this compound by using monochloracetone in the place of phenacylbromide. By the distillation of mucic acid or isosaccharic acid, furfurane-α-carboxylic acid (pyromucic acid), C4H3O·CO2H, is obtained; it crystallizes in needles or leaflets, and melts at 134° C.
Furfurol (furol), C4H3O·CHO, is the aldehyde of pyromucic acid, and is formed on distilling bran, sugar, wood and most carbohydrates with dilute sulphuric acid, or by distilling the pentoses with hydrochloric acid. It is a colourless liquid which boils at 162° C., and is moderately soluble in water; it turns brown on exposure to air and has a characteristic aromatic smell. It shows all the usual properties of an aldehyde, forming a bisulphite compound, an oxime and a hydrazone; whilst it can be reduced to the corresponding furfuryl alcohol by means of sodium amalgam, and oxidized to pyromucic acid by means of silver oxide. It also shows all the condensation reactions of benzaldehyde (q.v.); condensing with aldehydes and ketones in the presence of caustic soda to form more complex aldehydes and ketones with unsaturated side chains, such as furfuracrolein, C4H3O·CH:CH·CHO, and furfuracetone, C4H3O·CH:CH·CO·CH3. With alcoholic potassium cyanide It changes to furoin, C4H3O·CHOH·CO·C4H3O, which can be oxidized to furil, C4H3O·CO·CO·C4H3O, whilst alcoholic potash converts it into furfuryl alcohol. With fatty acids and acid anhydrides it gives the “Perkin” reaction (see Cinnamic Acid). Furfurol is shown to have its aldehydic group in the a position, by conversion into furfurpropionic acid, C4H3O·CH2·CH2·CO2H, which on oxidation by bromine water and subsequent reduction of the oxidized product is converted into n-pimelic acid, HO2C(CH2)5CO2H. Furfurol in minute quantities can be detected by the red colour it forms with a solution of aniline acetate.
Furfurane-αα′-dicarboxylic acid or dehydromucic acid, C4H2O(CO2H)2, is formed when mucic acid is heated with hydrochloric acid at 100° C. On being heated, it loses carbon dioxide and gives pyromucic acid. By digesting acetoacetic ester with sodium succinate and acetic anhydride, methronic acid, C8H8O5, is obtained; for the constitution of this acid, see L. Knorr, Ber., 1889, 22, p. 152, and R. Fittig, Ann., 1889, 259, p. 166.
Di- and tetrahydrofurfurane compounds are also known (see A. Lipp, Ber., 1889, 22, p. 1196; W. H. Perkin, junr. Journ. Chem. Soc., 1899, 57, p. 944; and S. Ruhemann, ibid., 1896, 69, p. 1383).