INDUSTRIAL USES OF FURANS FREDUS N. PETERS,JR. The Quaker Oats Company, Chicago, Ill.
N D U S T R I A L progress seldom proceeds in a straight line and many times apparently radical developments are merely the result of the application of some idea advanced many years before and forgotten. The development of the industrial uses of furfural and derivatives is no exception. These products are moderately young, but it is surprising how many applications haye been proposed, ut&ed for a short time, abandoned, and now almost forgotten. This paper is a brief and incomplete survey of the industrial uses of the furans, with emphasis placed on the little-known applications suggested in the literature. It is believed that by recalling these, along with some of the new developments, fresh viewpoints may be obtained.
by the screwworm fly. As a wash in poultry houses to kill lice and other parasites, it is as effective as formaldehyde and is easier to handle. Even embalming fluids for both human beings and biological specimens have been made with furfural. Other uses in these fields have been proposed, but the applications mentioned are enough to warrant the statement that further research in the field of the biological application of the furans is sure to be fruitful. At present probably less than a ton of this aldehyde is used annually for such purposes, and although this quantity is only a fraction of the present market, its importance should not be minimized.
Chemical Uses The uses of furfural involving its chemical properties are more promising, as far as large outlets are concerned. Its aldehydic nature suggested its use in phenolic resins, and for many Years synthetic resin manufacture consumed more than 50 Per Cent Of the furfural Produced. Phenol-furfural resins are superior to the formaldehyde analogs in Some respects; they are Particularly good from the standpoint of heat, acid, and alkali resistance, mechanical strength, and electrical properties. From the yield standpoint furfural also offers advantages. When 96 pounds of furfural and 94 pounds of phenol react, only 18 pounds of water are lost, whereas about 80 pounds of formaldehyde and 94 pounds of phenol liberate 68 pounds of water. At present furfural resins can be made more cheaply than formaldehyde resins. It is probably true also that if furfural resins were to receive one tenth the research effort expended on formaldehyde resins, tremendous and rapid advances in this field would be made. I n a t least one case furfural-phenol resins enjoy a practical monopoly-as a cement to seal electric light bulbs to the brass bases. Most of the light bulbs in the world today are made in this manner. Numerous other resins have been made from furfural and its derivatives. Thus furfural and furfuryl alcohol resinify with acids to form insoluble products, and this reaction affords an excellent means of impregnating porous materials with subsequent formation of a resin in situ. There is a patent suggesting the use of furfural with seaweed to form resins (1). Another describes the use of the resin obtained on evaporation of furfural as a coating composition for copper wire. Still others mention the applications of furfuryl methacrylate resins. Furfural may be oxidized to maleic acid which is used in the manufacture of alkyd resins. Lignin-furfural resins are also being investigated as a source of low-cost prefabricated building materials, and, as the cost of furfural decreases, the uses in these fields will become increasingly attractive. Recent literature describes ice colors ( I $ ) , cyanine (6), and alizarin (7) type dyes from furfural as well as the furan analogs (8) of malachite green, benzoflavine, and rosamine. Years ago the lead and zinc salts of dithiofuroic acid were used as vulcanization accelerators. This market disappeared, but within the past few years the number of patents describing accelerators made from furfuryl amines, tetrahydrofurfuryl amines, mercaptobenzothiazole derivatives of fur-
Biological Uses The biological classification includes preservatives, fungicides, herbicides, disinfectants, and therapeutic agents. Furfural is effective in preventing the growth of mold and bacteria in aqueous suspensions of starch, glue, and similar products. Generally it is a better fungicide than formaldehyde. Mercury hydrofuramide gives excellent control of Diplodia and other dry rot diseases which attack corn. Publications from the University of California indicate that many mercury derivatives of furfural are powerful germicides (9). When sprayed on sand beaches, furfural destroys fungi such as the organism which causes “swimmer’s itch.” A one per cent aqueous solution is said to clear up infection by the parasite causing athlete’s foot, and a mixture of talc, boric acid, and hydrofuramide not only prevents this infection but is frequently effective in the treatment of advanced cases of this as well as other similar skin troubles. Mixed with kerosene or light fuel oil, furfural is an excellent herbicide; very small amounts are effective in killing dandelions, and larger quantities are equally good for fairly large vegetation. Furan, tetrahydrofuran, and the corresponding methyl derivatives produce anesthesia when inhaled but are too toxic for general use (4, 11). Hydrofuramide has been proposed as a rat poison and is claimed to be nontoxic to domestic animals. Barbituric acid and hydantoin derivatives of furfural are the subject of a number of foreign patents issued within the past four years. In very recent literature some attention has been given to furyl-substituted cinchonic acids, such as the fury1 analog of atophan (6). Furfural is said to be a good bait for the Oriental fruit moth, and it has been used to prevent infection of dehorned cattle 178
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fural, and similar materials indicate renewed interest in this field. Furfural, hydrofuramide, and furil have been used as antioxidants in the rubber industry.
Solvent Uses The solvent uses of furfural may be divided into two fields(a) where simple solution is desired and (b) where selective solvent action is needed. Furfural, furfuryl alcohol, and tetrahydrofurfuryl alcohol are solvents for cellulose esters, vinyl compounds, many natural gums, phenolic resins, and in general for substances of an aromatic character. For years resin-bonded abrasive wheels have been made with furfural as the solvent, and lately furfuryl alcohol has come into the same field. Paint removers, lacquer solvents, and special high-boiling solvents have been formulated from furfural, furoic acid esters, and other derivatives. Esters and ethers of furfuryl and tetrahydrofurfuryl alcohols are said to be excellent plasticizers. A special case is terpene furoates which have been described within the past two years. Furfuryl alcohol was used as a carbon remover in internal
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combustion engines, but this use was discontinued, not because a better solvent was found, but because of the difficulty of storing the alcohol under the high-temperature conditions existing beneath the hood of an automobile. Many textile and industrial dyes are soluble in furfural. Certain arsenic compounds useful for preventing attack by termites and teredo may be carried into the wood with furfural as the solvent. Difficultly soluble compounds are frequently dispersed in tetrahydrofurfuryl alcohol, and the use of this solvent for therapeutic agents is awaiting more accurate data on the toxicity of the solvent. Another use based on the solvent properties of the furans is in the refrigerating industry. Dichlorofluoromethaneis soluble in tetrahydrofurfurylacetate from which it may be readily volatilized and reabsorbed time and time again. A number of years ago it was found that anthracene could be separated from phenanthrene and carbazole by the selective solvent action of furfural. The same solvent will remove the color bodies from crude wood rosin, and this process has revolutionized the wood rosin industry within the past ten years. Naphthenes, sulfur compounds, aromatics, and other undesirable constituents of oil are removed with furfural, and the national advertising cam-
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may be at least partially separated or refined with furfural or furfuryl alcohol. This field constitutes the largest outlet
for the furans today, and the end is not in sight.
Miscellaneous Uses The miscellaneous uses for furfural cover a multitude of industries. Textile wetting agents made from tetrahydrofurfuryl alcohol are common in Europe. Furfural may be employed as a pulping agent in the manufacture of paper. Patents have issued claiming it to be useful as a motor car and airplane fuel. Furfuryl alcohol (10) and tetrahydrofurfuryl alcohol (2) are mentioned in the patent literature as being excellent antifreezes. Furfuryl xanthate is a good flotation agent, and at one time it appeared likely that several tons per day of furfuryl alcohol would be used for making the xanthate. Furoic acid is said to be a good antiscorch in rubber manufacture, and furfural is applied in the preparation of certain anticreasing compositions. It is used as a demulsifying agent for oil mixtures, and its derivatives serve as emulsifying and degreasing agents in the textile field according to other patents. Improvement in “oiliness” of hydrocarbon lubricants (12) is claimed through addition of a furoic acid ester to the lubricant. One of the interesting and potentially large outlets for furfural is in the building of bituminous roads. Furfural alone, or a mixture of furfural and phenol or furfural and aniline, is added t o a mixture of bitumen and mineral aggregate. In the fimt place this addition results in better wetting action of the bitumen for the aggregate, and in the second place the adhesion is increased. It is also probable that subsequently a resinous film is formed which helps increase the weathering resistance of the bituminous surface. On an average it requires about one ton of furfural per mile of road. There is a real need for improvements in this field, and if future experiments check the results already obtained, furfural will be used in the construction of many miles of secondary roads. From lubricating oils to abrasive manufacture and from
anesthetics to road building there is practical and theoretical evidence of the value of the furans as industrial products. Two great factors militate against the fruition of many of these projects, price and lack of adequate research. Of these the economic factor is of least importance, for with sufficient volume furfural can be made a t an unbelievably low cost. Research is increasing. -4 prominent German chemist said recently that, if he had his way, he and his entire staff would spend all of their time in the field of furan chemistry. An equally prominent American chemist has predicted that within twenty-five years furan chemistry will be as well established industrially as benzene chemistry. -4lthough this may seem an exaggeration, it is perhaps closer than many of us realize.
Literature Cited (1) Aida, T., Japanese Patent 113,672 (Dec. 11, 1935). (2) Cairns, R. W. (to Firestone Tire and Rubber Co.),U. 8. Patent 1,992,469 (Feb. 26, 1935). (3) Feigin, Obleuckhova, and Prorokov, A’ejtganoe Khoz., 1936, NO. 3, 57-63. (4) Henderson, V. E., and Smith, A. H. R., J . Pharmcol., 57, 394 (1936). (5) I. G.Farbenindustrie A.-G., French Patent 777,034 (Feb. 9, 1935). (6) Mangini, A., Ann. chim. applicata, 27, 386 (1937). (7) Marschald, Ch., Koenig, F., and Ourousoff, N., Bull. SOC. chim., [5 ] 3, 1545-75 (1936). (8) Orlov, N. N., and Florova, T. I., J . Applied Chem. (U. S. S. R.), 9, 2039-49 (in German 2049) (1936). (9) Phatak, N. M., and Leake, C. D., J. Phannacol., 56, 266 and 58, 155 (1936). (10) Schenck, O., and Gellendien, W. (to Deutsche Hydrierwerke A.-G.), U. S. Patent 2,094,564 (8ept. 28, 1937). (11) Stoughton, R. W., and Robbins, E. J., J . Phannacol., 58, 171 (1936). (12) Zimmer, J. C., and Morway, A. J. (to Standard Oil Development Co.), U. s. Eatent 2,113,754 (April 12, 1938). (13) Zwilgmeyer, F. (to E. I. du Pont de Nemours & Co., Inc.), U. 8. Patent 2,064,332 (Dec. 15, 1936). RECEIVBDSeptember 12, 1938.
