Applications of Furfural

Of the many actual and potential applications of furfural, the treatment is limited to a few fields where furfural is used as it is. Cases where furfural is employed as an input material for the synthesis of other chemicals are not discussed in this chapter. It is merely noted that 65 percent of all furfural produced is converted to furfuryl alcohol. 

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From the treatment of seeds, the application of furfural as a fungicide was extended to growing plants and to wood. 

One such application of furfural is the extraction of vegetable oils such as soybean oil to get an extract rich in double bonds, and a raffinate depleted of double bonds. The extract rich in double bonds can be used as a drying oil for paints and varnishes, where the double bonds react with oxygen of the ambient air to form cross-linked polymers. On the other hand, the raffinate depleted of double bonds is a more desirable product for the food industry than the nonextracted soybean oil. Thus, two advantages are obtained in a single operation. 

Numerous applications of furfural as starting material for the production of bulk products have been reported (Scheme 21) [113]. Generally, two approaches can be distinguished. Products from biomass can be used to produce already existing... 

The chemistry of furfural is mainly determined by the aldehyde function and the heteroaromatic furan ring. Many chemical transformations are therefore similar to those of aromatic aldehydes. However, the aromatic character of the heterocycle is low when compared to isocyclic compounds such as benzene derivatives or other related heterocycles such as pyrroles and pyridines. Therefore, the furan ring also resembles to a diene which significantly enriches the chemistry of furfural [112]. Many applications of furfural to organic synthesis are reported in the literature... 

Therapeutics. Compounds containing the furan or tetrahydrofuran ring are biologically active and are present in a number of pharmaceutical products. Eurfurjdamine [617-89-0] is an intermediate in the diuretic, furosemide. Tetrahydrofurfurylamine [4795-29-3] may also have pharmaceutical applications. 5-(E)imethyiaininomethyi)furfuryi alcohol [15433-79-17 is an intermediate in the preparation of ranitidine, which is used for treating ulcers. 2-Acet5dfuran [1192-62-7] prepared from acetic anhydride and furan is an intermediate in the synthesis of cefuroxime, a penicillin derivative. 2-Euroic acid is prepared by the oxidation of furfural. Both furoic acid [88-14-2] and furoyl chloride [527-69-5] are used as pharmaceutical intermediates. 

Pure xylan is not employed in industry. but crude xylan or pentosans are of industrial importance. Xylan has been proposed as a textile size but is not employed as yet for this purpose.130 Perhaps the largest use of pentosans is in their conversion to furfural, which has many applications and serves as the source of other furan derivatives. At the present time, large quantities of furfural are used in the extractive purification of petroleum products, and recently a large plant has been constructed to convert furfural by a series of reactions to adipic acid and hexamethylene-diamine, basic ingredients in the synthesis of nylon. In commercial furfural manufacture, rough ground corn cobs are subjected to steam distillation in the presence of hydrochloric acid. As mentioned above, direct preferential hydrolysis of the pentosan in cobs or other pentosan-bearing products could be used for the commercial manufacture of D-xylose. 

Development of solvent extraction processes in the petroleum industry and theoretical aspects of solvent extraction are reviewed. Six extraction processes which have received industrial acceptance are described and performance characteristics of furfural, phenol, and Duosol processes are compared. Data are presented to demonstrate the applicability of adsorption analyses for stock evaluation and prediction of commercial extraction yields. Correlations for predicting solvent requirements and layer compositions and process design and engineering considerations are included. The desirability of further fundamental work to facilitate design calculations from physical data is suggested. 

Furfural Process. A patent involving furfural for solvent extraction of lubricating oils was issued to Eichwald of the Royal Dutch Shell Co. in 1925 (10). The first commercial application of the furfural process was at the Lawrenceville, 111., refinery of the Indian Refining Co. in December 1933. 

It was not until the twentieth century that furfural became important commercially. The Quaker Oats Company, in the process of looking for new and better uses for oat hulls found that acid hydrolysis resulted in the formation of furfural, and was able to develop an economical process for isolation and purification. In 1922 Quaker announced the availability of several tons per month. The first large-scale application was as a solvent for the purification of wood rosin. Since then, a number of furfural plants have been built world-wide for the production of furfural and downstream products. Some plants produce as litde as a few metric tons per year, the larger ones manufacture in excess of 20,000 metric tons. 

Furfural has been used as a component in many resin applications, most of them thermosetting. A comprehensive review of the patent literature describing these uses is beyond the scope of this review. A few, selected recent patents and journal articles have been referenced. Resins prepared from the condensation products of furfural with urea (47), formaldehyde (48), phenols (49,50), etc, modified by appropriate binders and fillers are described in the technical literature for earlier applications, see reference 1, which contains many references in an appendix. 

Other furan compounds, best derived from furfural, are of interest although commercial volumes are considerably less than those of furfural, furfuryl alcohol, furan, or tetrahydrofurfuryl alcohol. Some of these compounds are still in developmental stages. Applications include solvents, resin intermediates, synthetic mbber modifiers, therapeutic uses, as well as general chemical intermediates. 

The oxidation of furans has often been used to express the latent functionality present within this heterocyclic framework, and it results particularly attractive for the synthesis of the widespread butenolides [8c,56]. Dye-sensitized photo-oxygenation of furfural, furoic acid and a- or a,a -unsubstituted furans leads directly to butenolides [8c,56,60d,63]. The presence of a silyl group in a-position enhances the rate of endoperoxide formation and controls the regiochemical outcome of the second-step leading to the related butenolide via a rapid intramolecular silatropic shift [64]. An application of this reaction is shown in Sch. 39 as a step in the synthesis of spongianolide A, an antitumoral natural sestertepenoid [65],... 

Most furfural is produced from corncobs and oat and rice hulls, primarily by the Quaker Oats Company. The product is used in the chemical industry as a solvent and in wood rosin refining. A large amount of furfural is treated further to give furfuryl alcohol. The furfuryl alcohol is added to urea-formaldehyde resins in applications for adhesives and foundry core binders. 

Many industrial applications utilize the solvent properties of furfural and fur-furyl alcohol however, both chemicals also display unique features as monomers for condensation polymerization. Most of the furfuryl alcohol sold is used as monomer in the manufacture of resins for industrial application. 

Copolymers of furfural with phenol or phenol-formaldehyde polymers have been available commercially for many years. Since the acid-catalyzed reaction of furfural and phenol has been difficult to control, most industrial applications involve the use of alkaline catalysts. Furfural-phenol resins are used for their alkali resistance, enhanced thermal stability, and good electrical properties compared to phenol-formaldehyde resins. 

Such oxidants cause the syn hydroxylation of double bonds [310, 714, 715, 716] and convert triple bonds into vicinal carbonyls [717]. Other applications, such as the conversion of furfural into fumaric acid [716, 718] or the oxidation of hydroquinone to quinone [719], are rare. 

Application of this process to furfural waste water was studied in detail by Wirtz and Dague [44]. Contrary to widespread erroneous belief, these authors established beyond any doubt that at the concentrations occurring in furfural waste water, the toxicity of furfural for some microorganisms does not apply to methane bacteria. They not only thrive on acetic acid but eat up furfural as well. For the low concentrations of acetic acid in furfural waste water, these bacteria, known to decompose acetic acid to methane and carbon dioxide according to the reaction... 

The initiation of the reactions between phenol and furfural to form the resin can be catalyzed by both acid or alkali. As these reactions are exothermic, heat must be withdrawn at this stage. The final curing of the resin is universally triggered by the application of heat. 

While at present the principal applications of fiirfiiral are seen to be as an extractant for lubricating oils, vegetable oils, and diesel fuel, as a fungicide, as a nematocide, and as the raw material for furfuryl alcohol to make foundry resins, other uses have been proven successfully on a multitude of fronts, and it is only a lack of research which prevents furfural and its derivatives from flooding the world in a sturming variety of different applications. 

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