Furfural derivatives

Heating the sugar with strong acid yields furfural derivatives. Aldohexoses can eliminate water and formaldehyde under these conditions yielding furfural. This adehyde reacts with amines according to I to yield colored Schiff s bases. Ketohex-oses condense with diphenylamine in acid medium with simultaneous oxidation according to II to yield the condensation product shown. 

Heating the sugars with strong add yields furfural derivatives. Under these conditions aldohexoses can eliminate formaldehyde and water to yield furfural. This aldehyde reacts with amines to yield colored Schiff s bases. 

Furfural derivatives are produced when sugars are heated with acids (see Aniline —... 

The hexoses that are the initial products of acid hydrolysis of sucrose (1) react at el vated temperature under the influence of acids to yield furfural derivatives (2). Thed condense, for example, with the phenols to yield triarylmethanes (3), these react furthei by oxidizing to yield colored quinoid derivatives (2, 4). Polyhydric phenols, e. g. resorj cinol, on the other hand, yield condensation products of Types 5 and 6 [2],... 

Although highly reactive, 2/7-azirines are of considerable synthetic interest and serve as a source of the 3-fluoro-4//-l, 3-diazepines 86. Reaction of 80 with difluorocarbene in the presence of furfural gave 86, rather than the expected furfural-derived products 83. Rearrangement of the initial 1,3-dipolar intermediate 81 to 84 and then cycloaddition of 84 with 80 are proposed as key steps in the reaction the intermediate cycloadduct 85 gave 86 on base-induced elimination of HF. Nucleophilic displacement of the fluoro group in 86 provided access to further substituted 1,3-diazepines <06TL639>. 

Es-Safi, N.E., Cheynier, V., and Moutounet, M., Study of the reactions between (+)-catechin and furfural derivatives in the presence or absence of anthocyanins and their implication in food color change. J. Agric. Food Chem. 48, 5946, 2000. 

Methylfuran-3-thiol is responsible for a boiled note in milk, chicken and beef flavours and this chemical as well as its disulfide are widely used in flavours. Both molecules can be prepared by heating xylose and hydrogen sulfide in an autoclave (Scheme 13.13). Alternatively, these sulfur compounds can also be synthesised from 2-methylfuran made from furfural derived from oat hulls. 

Colour forming reactions also take place, in a variety of ways, between the photolysis products of haloalkanes and styryl dye bases such as the quinoline (153), a cyanine dye such as (154), or a furfural derivative such as (155). 

Many other odorous or volatile compounds, particularly furfural derivatives, nitrogenous compounds, and other phenols, have been identified in distilled beverages after barrel aging and not before (23), but their role is not yet clear. So far it appears that the components contributed by oak to wine and brandy probably are common to most mildly pleasant but not distinctively odorous hardwoods. They appear to be agreeably combined with a moderate tannin level and generally unaccompanied by any unpleasant tastes and odors in cooperage oak. 

Caramelization can occur under both acidic and basic conditions. Acids promote dehydration reactions resulting in the formation of furfural derivatives while alkalies favor isomerization and fragmentation reactions (6). 

This process was developed for cellulose-rich raw materials since high concentration of the acid may cause degradation of the pentoses in hemicellulose to furfural derivatives. The ethanol yield is usually about 35%. However, corrosion problems and the need for higher capital investment and dangers associated with the recovery of the concentrated acid make this method less attractive. Furthermore, during combustion of lignin that is contaminated with hydrochloric acid there is some risk of dioxin emissions. 

Diels-Alder reaction of furfural derivatives with 1,4-phthalazinedione followed by rearrangement and oxidation with Pb(OAc)4 provided [5,6]benza-3a,7a-diazaindane derivatives in moderate to good yields <02OL773>. 

From the molecular beam MS of the pyrolysis products of the P/N fractions, a number of phenolic compounds were detected guaiacol (2-methoxyphenol) (m/z 124), catechols (m/z 110), isomers of substituted 2-methoxyphenols with alkyl groups such as methyl (m/z 138), vinyl (m/z 150), 3-hydroxy-propen(l)-yl (m/z 180), allyl (m/z 164), hydroxyethyl (m/z 168), and ethyl (152), most likely in the para position. In addition, a few carbohydrate-derived components are also present in this fraction such as furfuryl alcohol and other furfural derivatives. 

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 proof for the formula XII is as follows. The full methylation of difructose anhydride III yielded a hexamethyl derivative, non-crystalline but readily distillable at 161-165° in a vacuum of 0.42 mm. The hydrolysis of hexamethyl-difructose anhydride III in 0.8 N aqueous hydrochloric acid at 95° appeared to reach half completion in about ninety-one minutes it is evident that the substance is rather difficult to hydrolyze. There i.s some destruction of the hydrolytic products in the acid solution with the formation of furfural derivatives, and it was found best to stop the hydrolysis at the half stage and separate the trimethyl-D-fructose fraction from the unhydrolyzed material by distillation in vacuo, the hydrolyzed products being more volatile the still residue was again hydrolyzed to the half stage and the separation repeated. In this manner there was obtained a yield of about 58% redistilled trimethyl-D-fructose, the specific rotation of which in chloroform is in the range = + 25-30°. Although this value is near that of pure 3,4,6-trimethyl-D-fructose, which is - - 26.6°, the agreement proved to be fortuitous because the sirup was not solely 3,4,6-trimethyl-D-fructose. It contained 3,4,6-trimethyl-D-fructose (readily identified by oxidation to... 

Assembly of Diels-Mder reaction components using a Ugi reaction Furfural and related compounds (293) can serve as diene building blocks in intramolecular and intermolecular cycloadditions, as they can be attached to resin-bound amines by reductive amination [306]. Particularly versatile is the use of furfural derivatives in 4-component Ugi reactions, where the diene and the dienophile component can be present. However, in the reaction set-up the electronic characteristics of the building blocks such as HOMO/LUMO energy or electron demand have to be considered to receive high yields. In the study presented by Schreiber et al., an acrylic acid served as dienophile (Scheme 64) [307]. 

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