5- Hydroxymethyl-2-furaldehyde

Functional tests, for enzyme purity, 286 Fungi, polysaccharides of, 367—417 2-Furaldehyde, 5-(hydroxymethyl)-, from cellulose on pyrolysis, 432 Furan, tetrahydro-, as solvent in lithium... 

Pentoses have frequently been determined in soils by the furfural-phloro-glucinol method.But phloroglucinol also gives precipitates with a variety of other aldehydes, such as 5-methyl-2-furaldehyde, 5-(hydroxymethyl)-2-furaldehyde, and formaldehyde. Orcinol and aniline acetate are much more specific reagents, and no aldehyde present in the hydrochloric acid distillate from soils has been found to interfere in the furfural determination by the orcinol method. The orcinol and aniline acetate methods give, for various Swiss and Norwegian soils, a pentose anhydride content of 0.5 to 8.5 % of the soil organic matter (see Table III) no corrections were made for the furfural derived from uronic acids. 

The chemical composition of caramel color is not yet fully understood but some compounds identified in the low weight fraction are considered caramel markers. All caramel classes contain 5-hydroxymethyl)-2-furaldehyde (5-HMF). In caramel classes in and TV, 4-methyUmidazole (4-MeI) has been detected, while 2-acetyl-4(5)-tetrahydroxybutylimidazole (THI) was found only in class HI caramel colors. The analysis of five caramel III samples by SPE/HPLC-MS revealed concentrations between 28.3 and 46.8 iglg THI and 73.3 to 187.8 for 4-MeP (see Figure 5.2.3). 

Jaganathan, J. and Dugar, S.M., Authentication of straight whiskey by determination of the ratio of furfural to 5-hydroxymethyl-2-furaldehyde, JAOC Int., 82, 997, 1999. Wang, R. and Schroeder, S.R., The effect of caramel coloring on the multiple degradation pathways of aspartame, J. Food Sci. 65, 1100, 2000. 

Vinas, P., CampiUo, N., Hernandez Cordoba, M., and Candela, M. E. (1992). Simultaneous liquid chromatographic analysis of 5-hydroxymethyl-2-furaldehyde and methyl anthra-nilate in honey. Food Chem. 44, 67-72. 

AW, Acid-washed Choi, Cholesterol DMAP, 4-(Dimethylamino)pyridine DMF, N,/V-Dimethylformamide DMTr, Di(p-niethoxyphenyl)phenyl methyl GalNAc, N-Acetylgalactosamine, 2-acetamido-2-deoxy-D-galactose HMF, 5-Hydroxymethylfur-fural, 5-(hydroxymethyl)-2-furaldehyde INOC, Intramolecular nitrile oxide-alkene cycloaddition Lea, Lewisa Lex, Lewisx MOM, Methoxymethyl MP, p-Methoxyphe-nyl MS, Molecular sieves NIS, N-Iodosuccinimide PCC, Pyridinium chlorochromate PDC, Pyridinium dichromate PMA, Phosphomolybdic acid PMB, p-Methoxybenzyl ... 

The reaction mechanism postulated by Wolfrom, Schuetz and Cavalieri87 for the formation of 5-(hydroxymethyl)-2-furaldehyde from D-glucose involves the enol (XXXV) of 3-deoxy-D-glucosone as an intermediate an alternative pathway proposed by these same workers included the enol... 

With regard to the formation of levulinic acid by acid treatment of 5-(hydroxymethyl)-2-furaldehyde, Pummerer, Guyot and Birkofer92 pro-... 

Neher and Lewis177 obtained 2-furaldehyde from 2,3,4-tri-O-methyl-L-arabinose by heating with dilute acid after preliminary enolization with alkali. Isbell83 proposed a mechanism for this conversion similar to that for the conversion of tetra-0-methyl-(2-hydroxy-D-glucal) into 5-(hydroxymethyl)-2-furaldehyde XLIV was suggested as an intermediate. In Hurd and Isenhour s178 scheme for the formation of 2-furaldehyde from free pentose, the enol (XLV) of a 3-deoxypentosone was regarded as an inter-... 

D-Erythrose has also been exposed to a boiling solution in pH 4.5 buffer. Low yields (<0.2%) of a number of products were obtained, as shown in Scheme 3. These included 5-(hydroxymethyl)-2-furaldehyde (11), 2-acetyl-5-(hydroxymethyl)furan (12), 3,4-dihydroxyacetophenone (13), 3,4-dihydroxy be nzaldehyde (14), 3,4-dihydroxybenzoic acid (15), 2,3-dihydroxytoluene (16), and 1,2-benzenediol (pyrocatechol) (17). Also detected were formic, hydroxyacetic, and 3-hydroxypropanoic acids. Pyrocatechol seems to be a product formed from all carbohydrates boiled in aqueous solutions at pH 4-10 it may constitute a statistical product arising from retro-aldol and re-aldol reactions. It has been shown that the aldol reaction may operate at a pH as low as 4. An aldol reaction... 

Scheme 7.—Formation of 5-(Hydroxymethyl)-2-furaldehyde from o-Glucose.

D-glucose and D-fructose in acidified deuterium oxide, and acid conversion of D-[2- H]glucose were conducted, in order to determine the importance of 39 as an intermediate from the proportion of deuterium incorporated at C-3 of 5-(hydroxymethyl)-2-furaldehyde. However, the 2-furaldehyde formed in the reactions contained no deuterium. Thus, an essentially irreversible sequence that involves hexose, 36, 38, 40, and 11 best explains the acid-catalyzed, dehydration reaction. 

Thermolysis of D-fructose in acid solution provides 11 and 2-(2-hydrox-yacetyl)furan (44) as major products. Earlier work had established the presence of 44 in the product mixtures obtained after acid-catalyzed dehydrations of D-glucose and sucrose. Eleven other products were identified in the D-fructose reaction-mixture, including formic acid, acetic acid, 2-furaldehyde, levulinic acid, 2-acetyl-3-hydroxyfuran (isomaltol), and 4-hydroxy-2-(hydroxymethyl)-5-methyl-3(2//)-furanone (59). Acetic acid and formic acid can be formed by an acid-catalyzed decomposition of 2-acetyl-3-hydroxyfuran, whereas levulinic acid is a degradation prod-uct of 11. 2,3-Dihydro-3,5-dihydroxy-6-methyl-4//-pyran-4-one has also been isolated after acid treatment of D-fructose.The pyranone is a dehydration product of the pyranose form of l-deoxy-D-eo f o-2,3-hexodiulose. In aqueous acid seems to be the major reaction product of the pyranone. 

The acyclic, enolic compounds 7 and 9 may exist in either cis or trans forms. Methyl ethers of 7 have been isolated in the cis form,8 but it is not known whether the trans forms, which must be acyclic, exist. The relative proportion of isomers is controlled by the geometry of the parent sugar enediol. Although the acyclic forms are readily interconvertible tautomers, it appears that, in acidic medium, further reaction occurs much more rapidly than any equilibrating reactions. Compound 7 undergoes rapid elimination of a second hydroxyl group to give 11. This acyclic product, also, may exist as either a cis or a trans isomer, both forms of which have been isolated.8 The loss of a third molecule of water per molecule occurs after, or simultaneously with, the cyclization of 11 (see Section II, 3 p. 171), and results in formation of 5-(hydroxymethyl)-2-furaldehyde (5). 

The major products formed from hexoses that react in aqueous acidic solution are 5-(hydroxymethyl)-2-furaldehyde, levulinic acid, and polymeric materials. In addition, many minor dehydration products are found. In a study41 of D-fructose, 2-(2-hydroxyacetyl)furan (13), 2-acetyl-3-hydroxyfuran (isomaltol 16), 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one, and 3,4,5-trihydroxy-3,5-hexadien-2-one (acetylformoin) were identified. Products not formed solely by dehydration mechanisms include acetone,56 formaldehyde, acetalde-... 

D-glucose or D-fructose into 5-(hydroxymethyl)-2-furaldehyde in solution in acidified deuterium oxide.17 The 2-furaldehyde was isolated as 5-(hydroxymethyl)-2-furoic acid, and thus this experiment did not permit an evaluation of reversible equilibration of 1,2-enediols with the parent sugars. However, the 2-furoic acid was devoid of measurable carbon-bound deuterium, which indicated the absence of 3-deoxyglycosulose intermediates. It is also noteworthy that 3-deoxy-D-en/fhro-hexosulose is converted, in acidified deuterium oxide, into 5-(hydroxymethyl)-2-furaldehyde with no solvent exchange84 this result lends further support to the conclusion that 45 does not participate in the reaction as an intermediate. 

The formation both of 5-formyl-2-furoic acid (74) and 2-furaldehyde could result by way of the formation of the 2,5-dihydrofuran 73. Elimination of the C-5 proton and the 2-hydroxyl group by a reaction analogous to that for the formation of 5-(hydroxymethyl)-2-furalde-hyde yields 74, whereas decarboxylation, as shown, results in 2-furaldehyde. Once formed, 73 would be expected to give higher yields of 74 than of 27 this implies that decarboxylation occurs prior to ring formation. 

Obviously, a similar mechanism can be presented for the formation of carbocyclic compounds from the hexoses, but less is known about the products and the variation in their distribution within the group. Most of the work with the hexoses has been conducted with D-glucose and D-fructose. It is known that D-mannose and D-galactose give significantly lower yields of 5-(hydroxymethyl)-2-furaldehyde than either D-glucose or D-fructose when treated in concentrated sulfuric acid,52 but no homolog of 75 has been reported. 

When heated in aqueous acidic medium, D-glucose, 2-deoxy-D-erythro-pentose, furfuryl alcohol, 5-(hydroxymethyl)-2-furaldehyde, and five-carbon glycals yield levulinic acid. Because of the importance of developing tests for 2-deoxy-D-en/ihro-pentose, the reactions have been extensively studied, and several mechanisms have been suggested.3,198-208 For converting furfuryl alcohol (101) into levulinic... 

In the 78-92% range of concentration of sulfuric acid, the molar absorptivity of 5-(hydroxymethyl)-2-furaldehyde increases at an average rate of 4% per 1% change in the concentration of the acid the wavelength of the absorption maximum changes from 290 to 320 nm. 

D-Xylose was found to yield 2-furaldehyde almost exclusively, but D-lyxose, D-ribose, and L-arabinose produce another, as yet unidentified, compound absorbing at 289 nm, which is the maximum absorption wavelength for reductic acid. D-Glucose, D-fructose, and sucrose give almost identical yields (—85%) of 5-(hydroxymethyl)-2-fural-dehyde, but D-galactose and D-mannose give much lower yields thereof. 

Because, on treatment with the anthrone reagents,224,225 hexoses and 5-(hydroxymethyl)-2-furaldehyde give solutions having identical spectral characteristics, dehydration is indicated to be the important reaction in this analysis. This conclusion is further supported by the reported isolation228 of 10-furfurylidene-9,10-dihydro-9-oxoanthra-cene (121) after reaction of 2-furaldehyde with anthrone, and by the fact that 121 has an absorption maximum of 600 nm, a value close to that used for pentose estimations. In similar studies,227 9,10-dihydro-10-(5-methylfurfurylidene)-9-oxoanthracene (122) was reported to have been isolated after the reaction of either L-rhamnose or 5-methyl-... 

D-glucose, and 5-(hydroxymethyl)-2-furaldehyde with anthrone lends support to these conclusions, and further indicates the complexity of the overall reaction. In the reaction of either D-fructose or 5-(hy-droxymethyl)-2-furaldehyde with anthrone, at least nine compounds were observed, three of which were condensation products of anthrone itself. The other products had absorption maxima ranging from 490 to 770 nm (in sulfuric acid solution and under the conditions of the anthrone reaction). One of the prominent pigments, having a blue color ( max 620 nm) and a postulated structure corresponding to compound 123, was isolated and characterized by its nuclear magnetic... 

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