Decarbonylation of furfural

Manufacture. Furan is produced commercially by decarbonylation of furfural in the presence of a noble metal catalyst (97—100). Nickel or cobalt catalysts have also been reported (101—103) as weU as noncatalytic pyrolysis at high temperature. Furan can also be prepared by decarboxylation of 2-furoic acid this method is usually considered a laboratory procedure. 

Furan is synthesized by decarbonylation of furfural (furfuraldehyde), which itself can be prepared by acidic dehydration of the pentose sugars found in oat hulls, corncobs and rice hulls. 

Furan carboxylic acids usually decarboxylate readily, and this method is often used in the laboratory for the preparation of furans. Furan itself can be obtained in good yield from 2-furoic acid in quinoline, with a copper catalyst, while industrial methods employ the catalytic decarbonylation of furfural. Copper powder, copper oxide or copper bronze, or heavy metal oxides,22 are the best catalysts, in combination with quinoline as solvent and weak base.23-28 Dann et al,2fl decarboxylated 2,5-dimethyl-3-furoic acid in 50% yield using barium hydroxide. 3-Furoic acid, which is difficult to obtain in large quantities, is best prepared by controlled decarboxylation of the easily prepared furan tetracarboxylic acid. 

The decarbonylation of furfural to give furan is best carried out at rather high temperatures. The following catalysts have been described Pd or Pd on charcoal,30 calcium oxide,31 32 zinc and iron chromite,33 or zinc, chromium, and manganese oxide (from ammonium chromate and manganese nitrate).34 The optimum reaction temperature with... 

Furfural 69 has been used as a chemical feedstock for the production of furan via two production methods involving the decarbonylation of furfural <2005MI7>. Processes in both the liquid and gas phases were described for the preparation of furan through the decarbonylation of furfural using noble metal and metal oxide catalysts. The results of the study led the authors to state that the research trends for preparing furan based on the decarbonylation of furfural should mainly be concentrated on more effective catalysts and environmentally friendly processes. 

Furan has also been labeled with heavy water on supported catalysts (chromium, zinc, and manganese oxides promoted with K2C03) at a temperature of 350°.117 Deuterated furan has also been obtained from the vapor phase decarbonylation of furfural over mixed oxide catalysts in the presence of heavy water. Both of these systems utilize extreme experimental conditions and the methods outlined in Table XII are to be preferred for preparative labeling. 

Furans are volatile, fairly stable compounds with pleasant odours. Furan itself is slightly soluble in water. It is readily available, and its commercial importance is mainly due to its role as the precursor of the very widely used solvent tetrahydrofuran (THF). Furan is produced by the gas-phase decarbonylation of furfural (2-formylfuran, furan-2-carboxaldehyde), which in turn is prepared in very large quantities by the action of acids on vegetable residues mainly from the manufacture of porridge oats and cornflakes. Furfural was first prepared in this way as far back as 1831 and its name is derived from furfur which is the latin word for bran in due course, in 1870, the word furan was coined from the same root. 

Tetrahydrofuran (THF) is produced by decarbonylation of furfural to furan followed by catalytic hydrogenation. THF is applied as a solvent for resins and plastics, film castings and adhesives. THF also acts as a solvent in different fine organic syntheses on a commercial scale and as a chemical intermediate. Environmental demands increase the THF application cost because THF users must install solvent recovery systems. A high price and environmental considerations will limit the future growth of THF market. 

At one time, a raw material for the production of hexamethylenediamine was the pentose-based polysaccharides of agricultural wastes such as oat hulls. Treatment of these wastes with sulfuric acid or hydrochloric acid gives furfural. Decarbonylation of furfural over a zinc-chromium-molybdenum catalyst gives furan. Propose reagents and experimental conditions for the conversion of furan to hexamethylenediamine. 

Decarbonylation. Furfural is easily obtained from biomass waste such as oat and rice hulls that are rich in pentosans. Further valorisation of furfural can be done by decarbonylation to produce furan, which can be further converted into tetrahydrofuran by catalytic hydrogenation. 

Pure decarbonylation typically employs noble metal catalysts. Carbon supported palladium, in particular, is highly elfective for furan and CO formation.Typically, alkali carbonates are added as promoters for the palladium catalyst.The decarbonylation reaction can be carried out at reflux conditions in pure furfural (165 °C), which achieves continuous removal of CO and furan from the reactor. However, a continuous flow system at 159-162 °C gave the highest activity of 36 kg furan per gram of palladium with potassium carbonate added as promoter. In oxidative decarbonylation, gaseous furfural and steam is passed over a catalyst at high temperatures (300 00 °C). Typical catalysts are zinc-iron chromite or zinc-manganese chromite catalyst and furfural can be obtained in yields of... 

Furan is most readily prepared by decarbonylation (elimination of carbon monoxide) of furfural (furfuraldehyde), which in turn is made by the treatment of oat hulls, corncobs, or rice hulls with hot hydrochloric acid. In the latter reaction pentosans (polypentosides) are hydrolyzed to pentoses, which then undergo dehydration and cyclization to form furfural. 

The direct conversion into furfuryl alcohol, methylfuran and furan via metal-catalyzed hydrogenation, reduction and decarbonylation positions furfural as a strategic and ultimate industrial source for the production of a wide range of derivatives. Furfuryl amine, furoic acid, alpha-methylfurfuryl alcohol can be produced in one step from furfural. Other important fine chemicals are 2-acetylfuran, 2,5-dimethoxydihydrofuran, 5-dimethylaminomethylfurfuryI alcohol, and others. 

Finally, tetrahydrofuran (THF) can be obtained by decarbonylation of the carbonyl group of furfural under reductive conditions using Pd-based catalysts followed by hydrogenation of furan formed in the presence of a variety of metal catalysts (Sitthisa and Resasco, 2011). 

Furan is produced from furfural commercially by decarbonylation loss of carbon monoxide from furfural gives furan direcdy. Tetrahydrofuran (3) is the saturated analogue containing no double bonds. 

Tetrahydrofuran (3) is produced commercially from furfural by decarbonylation followed by hydrogenation it is also produced by several different methods from other raw materials. A complete discussion of tetrahydrofuran is found under Ethers. Polymers of tetrahydrofuran are covered under the general topic. Polyethers. Several other compounds containing the tetrahydrofuran ring, which are most readily produced from furfural, are discussed here. 

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... 

As can be seen, most of the furfural produced in this country is consumed as an intermediate for other chemicals. Hydrogenation to furfuryl alcohol is the largest use. Some of the furfuryl alcohol is further hydrogenated to produce tetrahydrofurfuryl alcohol. The next major product is furan, produced by decarbonylation. Furan is a chemical intermediate, most of it is hydrogenated to tetrahydrofuran, which in turn is polymerized to produce polytetramethylene ether glycol (PTMEG). 

On a commercial scale, furan is obtained from 2-formylfuran (furfural, furan-2-carbaldehyde) (see Section 6.2.7) by gas-phase decarbonylation, but in the laboratory, furans can be formed by the cyclodehydration of 1,4-dicarbonyl compounds. Heating in boiling benzene with a trace of /7-toluenesulfonic acid as a catalyst in a Dean-Stark apparatus is often effective (Scheme 6.30a). 

The preceding sections described the newer methods for the synthesis of furan and its derivatives. This section snmmariy.es the best practical methods for the synthesis of the parent furan and benzofuran ring structures and their substituted derivatives. It is from furfural that furan itself is prepared industrially by the catalytic decarbonylation in steam. 

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