Furfural reactions

This reaction is extremely sensitive, freshly distilled pure aniline should be used and the acetic acid should be pure and should not give the furfural reaction Spirits which have been stored in wooden casks give with aniline acetate a yellow coloration which disturbs the reaction, in such cases the spirit should be distilled before testing... 

Pekala, R.W., Alviso, C.T., Lu, X., Gross, J. and Fricke, J., New Organic Aerogels Based Upon a Phenolic-Furfural Reaction. Journal of Non-Crystalline Solids, 1995.188(1-2) p. 34—40. 

Pekala RW, Alviso CT, Lu X, Gross J, Fricke J (1995) New organic aerogels based upon a phenoUc-furfural reaction. J Non-Cryst Solids 188 34-40. 

RW Pekala, CT Alviso, X Lu, J Gross, J Fricke, New organic aerogels based upon a phenolic-furfural reaction J Non-Cryst Sohds 188 (1995) 34-40 US Pat Nos. 6,090,861 and 6,077,876... 

A red colored pyrroline dye (IV, Formula 4.92) could be identified in a model reaction of furfural and alanine. This dye is formed from 4 molecules of furfural and 1 molecule of alanine. Labehng experiments with showed that one open-chain molecule of furfural is inserted into the pyrrohnone structure. The prohne/furfural reaction system indicated further that ring opening proceeds via a cyanine dye with the structure illustrated in V, Formula 4.93. Other colored compounds could be obtained by the condensation of 3,5-dihydroxy-2-methyl-5,6-dihydropyran-4-one with furfural (VI, Formula 4.94) and of 3-hy-droxy-4-methy 1-3-cy clopenten-1,2-dione (met-... 

C. Fumaric acid from furfural. Place in a 1-litre three-necked flask, fitted with a reflux condenser, a mechanical stirrer and a thermometer, 112 5 g. of sodium chlorate, 250 ml. of water and 0 -5 g. of vanadium pentoxide catalyst (1), Set the stirrer in motion, heat the flask on an asbestos-centred wire gauze to 70-75°, and add 4 ml. of 50 g. (43 ml.) of technical furfural. As soon as the vigorous reaction commences (2) bvi not before, add the remainder of the furfural through a dropping funnel, inserted into the top of the condenser by means of a grooved cork, at such a rate that the vigorous reaction is maintained (25-30 minutes). Then heat the reaction mixture at 70-75° for 5-6 hours (3) and allow to stand overnight at the laboratory temperature. Filter the crystalline fumaric acid with suction, and wash it with a little cold water (4). Recrystallise the crude fumaric acid from about 300 ml. of iif-hydrochloric acid, and dry the crystals (26 g.) at 100°. The m.p. in a sealed capillary tube is 282-284°. A further recrystaUisation raises the m.p. to 286-287°. 

When the vigorous reaction commences, the temperature rises to about 105° and remains at this temp>erature for some time. The main quantity of furfural should not be added until the vigorous reaction has started if this precaution is ignored, an explosion may result. 

The analogous dismutation of furfural is described in Section V,8. For crossed Cannizzaro reaction , see discussion following Section IV,199. 

Furfural undergoes the Cannizzaro reaction (compare Benzaldehyde Section IV,123) when treated with sodium hydroxide solution ... 

Place 200 g. (172 -5 ml.) of redistilled furfural (1) in a 1 litre beaker, provided with a mechanical stirrer and surrounded by an ice bath. Start the stirrer and, when the temperature has fallen to 5-8°, add a solution of 50 g. of sodium hydroxide in 100 ml. of water from a separatory funnel at such a rate that the temperature of the reaction mixture does not rise above 20° (20-25 minutes) continue the stirring for a further 1 hour. Much sodium furoate separates during the reaction. Allow to cool to room temperature, and add just enough water to dissolve the precipitate (about 65 ml.). Extract the solution at least five times with 60 ml. portions of ether in order to remove the furfuryl alcohol the best results are obtained by the use of the continuous extraction apparatus (charged with 350 ml. of ether) depicted in Fig. //, 44, 2. Keep the aqueous layer. Dry the ethereal extract with a httle anhydrous... 

Furfural condenses with acetic anhydride and potassiuiu acetate to give furylacrylic acid (compare Perkin reaction, Cinnamic Acid, Section IV, 124) ... 

Method 2. Place 48 g. (41 -5 ml.) of freshly-distilled furfural, 52 g. of dry malonic acid (1), and 24 ml. of dry pyridine (2) in a 500 ml. round-bottomed flask, fitted with a reflux condenser. Heat the flask on a boiling water bath for 2 hours, cool the reaction mixture and dilute with 50 ml. of water. Dissolve the acid by the addition of concentrated ammonia solution, filter the solution and wash the filter paper with a... 

Furfural can be classified as a reactive solvent. It resiniftes in the presence of strong acid the reaction is accelerated by heat. Furfural is an excellent solvent for many organic materials, especially resins and polymers. On catalyzation and curing of such a solution, a hard rigid matrix results, which does not soften on heating and is not affected by most solvents and corrosive chemicals. 

Furfural can be oxidized to 2-furoic acid [88-14-2] reduced to 2-furanmethanol [98-00-0] referred to herein as furfuryl alcohol, or converted to furan by decarbonylation over selected catalysts. With concentrated sodium hydroxide, furfural undergoes the Cannizzaro reaction yielding both 2-furfuryl alcohol and sodium 2-furoate [57273-36-6]. 

Acetals are readily formed with alcohols and cycHc acetals with 1,2 and 1,3-diols (19). Furfural reacts with poly(vinyl alcohol) under acid catalysis to effect acetalization of the hydroxyl groups (20,21). Reaction with acetic anhydride under appropriate conditions gives the acylal, furfuryUdene diacetate... 

Nitration and halogenation of furfural occurs under carehiUy controlled conditions with introduction of the substituent at the open 5-position (24,25). Nitration of furfural is usually carried out in the presence of acetic anhydride, resulting in the stable compound, 5-nitrofurfuryhdene diacetate (26,27). The free aldehyde is isolated by hydrolysis and must be used immediately in a reaction because it is not very stable. 

Several early interpretations of the polymerization mechanism have been proposed (1,17,29—31). Because of the complexity of this polymerization and insoluble character of the products, key intermediates have not ordinarily been isolated, nor have the products been characterized. Later work, however, on the resinification of furfural (32,33) has provided a new insight on the polymerization mechanism, particularly with respect to thermal reaction at 100—250°C in the absence of air. Based on the isolation and characterization of two intermediate products (9) and (10), stmcture (11) was proposed for the final resin. This work also explains the color produced during resinification, which always is a characteristic of the final polymer (33). The resinification chemistry is discussed in a recent review (5). 

Strong inorganic acid can be used as a reaction catalyst, or if the temperature is raised high enough, sufficient acetic acid is produced by the heat to cataly2e formation of furfural. 

Uses. Furfural is primarily a chemical feedstock for a number of monomeric compounds and resins. One route produces furan by decarbonylation. Tetrahydrofuran is derived from furan by hydrogenation. Polytetramethylene ether glycol [25190-06-1] is manufactured from tetrahydrofuran by a ring opening polymeri2ation reaction. Another route (hydrogenation) produces furfuryl alcohol, tetrahydrofurfuryl alcohol, 2-methylfuran, and 2-methyltetrahydrofuran. A variety of proprietary synthetic resins are manufactured from furfural and/or furfuryl alcohol. Other... 

Useful thermosetting resins are obtained by interaction of furfural with phenol. The reaction occurs under both acidic and basic catalysis. Other large uses of furfural together with phenol are in the manufacture of resin-bonded grinding wheels and coated abrasives (5). 

Resins. As mentioned above, both furfural and furfuryl alcohol are widely used in resin apphcations. Another resin former, 2,5-furandimethanol [1883-75-6] (BHME), is prepared from furfuryl alcohol by reaction with formaldehyde. It is usually not isolated because oligomerization occurs simultaneously with formation (competing reaction). Both the monomer and oligomers are very reactive owing to difuntionahty, and are used primarily as binders for foundry sand (72) and fiberglass insulation (147,148). 

In the now-obsolete furfural process, furfural was decarboxylated to furan which was then hydrogenated to tetrahydrofuran (THF). Reaction of THF with hydrogen chloride produced dichlorobutene. Adiponitrile was produced by the reaction of sodium cyanide with the dichlorobutene. The overall yield from furfural to adiponitrile was around 75%. 

Schiff s bases of etbyleneimine dimer are obtained from the reaction of aromatic aldehydes, eg, ben2aldehyde [100-52-7] or furfural [98-01-00] and ethyleneimine (228). 

Examples include acetaldehyde, CH CHO paraldehyde, (CH CHO) glyoxal, OCH—CHO and furfural. The reaction is usually kept on the acid side to minimize aldol formation. Furfural resins, however, are prepared with alkaline catalysts because furfural self-condenses under acid conditions to form a gel. 

The versatility of this reaction is extended to a variety of aldehydes. The bisphenol derived from 2,6-di-/ f2 -butylphenol and furfural, (25) where R = furfuryl (13), is also used as an antioxidant. The utility of the 3,5-di-/ f2 -butyl-4-hydroxyben2yl moiety is evident in stabili2ets of all types (14), and its effectiveness has spurred investigations of derivatives of hindered alkylphenols to achieve better stahi1i2ing quaUties. Another example is the Michael addition of 2,6-di-/ f2 -butyl phenol to methyl acrylate. This reaction is carried out under basic conditions and yields methyl... 

These precursors are prepared by reaction of fuming nitric acid in excess acetic anhydride at low temperatures with 2-furancarboxaldehyde [98-01-1] (furfural) or its diacetate (16) followed by treatment of an intermediate 2-acetoxy-2,5-dihydrofuran [63848-92-0] with pyridine (17). This process has been improved by the use of concentrated nitric acid (18,19), as well as catalytic amounts of phosphoms pentoxide, trichloride, and oxychloride (20), and sulfuric acid (21). Orthophosphoric acid, -toluenesulfonic acid, arsenic acid, boric acid, and stibonic acid, among others are useful additives for the nitration of furfural with acetyl nitrate. Hydrolysis of 5-nitro-2-furancarboxyaldehyde diacetate [92-55-7] with aqueous mineral acids provides the aldehyde which is suitable for use without additional purification. 

In acidic solution, the degradation results in the formation of furfural, furfuryl alcohol, 2-furoic acid, 3-hydroxyfurfural, furoin, 2-methyl-3,8-dihydroxychroman, ethylglyoxal, and several condensation products (36). Many metals, especially copper, cataly2e the oxidation of L-ascorbic acid. Oxalic acid and copper form a chelate complex which prevents the ascorbic acid-copper-complex formation and therefore oxalic acid inhibits effectively the oxidation of L-ascorbic acid. L-Ascorbic acid can also be stabilized with metaphosphoric acid, amino acids, 8-hydroxyquinoline, glycols, sugars, and trichloracetic acid (38). Another catalytic reaction which accounts for loss of L-ascorbic acid occurs with enzymes, eg, L-ascorbic acid oxidase, a copper protein-containing enzyme. 

Maltol. Otsuka Chemical Co. in Japan has operated several electroorganic processes on a small commercial scale. It has used plate and frame and aimular cells at currents in the range of 4500—6000 A (133). The process for the synthesis of maltol [118-71 -8], a food additive and flavor enhancer, starts from furfural [98-01-1] (see Food additives Flavors and spices). The electrochemical step is the oxidation of a-methylfurfural to give a cycHc acetal. The remaining reaction sequence is acid-catalyzed ring expansion, epoxidation with hydrogen peroxide, and then acid-catalyzed rearrangement to yield maltol, ie ... 

Furfural — see Furan-2-oarbaldehyde, 532 Furfuryl acetate, o -(butoxycarbonyl)-anodic oxidation, 1, 424 Furfuryi acrylate polymerization, 1, 279 Furfuryl alcohol configuration, 4, 544 2-Furfuryl alcohol polyoondensation, 1, 278 reactions, 4, 70-71 Furfuryl alcohol, dihydro-pyran-4-one synthesis from, 3, 815 Furfuryl alcohol, tetrahydro-polymers, 1, 276 rearrangement, 3, 773 Furfuryl chloride reactions... 

Dehydrogenation processes in particular have been studied, with conversions in most cases well beyond thermodynamic equihbrium Ethane to ethylene, propane to propylene, water-gas shirt reaction CO -I- H9O CO9 + H9, ethylbenzene to styrene, cyclohexane to benzene, and others. Some hydrogenations and oxidations also show improvement in yields in the presence of catalytic membranes, although it is not obvious why the yields should be better since no separation is involved hydrogenation of nitrobenzene to aniline, of cyclopentadiene to cyclopentene, of furfural to furfuryl alcohol, and so on oxidation of ethylene to acetaldehyde, of methanol to formaldehyde, and so on. 

---