Hydroxymethylfuran-2-aldehyde

In strongly acidic media, saccharides produce furan derivatives in a sequence of reactions that are rearrangements and dehydrations followed by cyclization. Similar products are available thermally. Pentoses and hexoses give furan-2-aldehyde and 5-hydroxymethylfuran-2-aldehyde, respectively. Both of these products are responsible for the specific aroma of caramel and burnt sugar. 

If not utilized in the pulp industry, hemicelluloses are hydrolyzed in the acid-catalyzed process, mainly to monosaccharides and to furan-2-aldehyde (pen-tosanes) and 5-hydroxymethylfuran-2-aldehyde (5.62) (hexosanes). Monosaccharide-containing syrups, after purification, are either fermented or utilized as wood molasses for feeding ruminants. In another approach, xylose, the least soluble component of syrup, is allowed to crystallize. Separated xylose is then hydrogenated over an Ni/Al catalyst at 120°C under 6 x 106 Pa into xylitol. Hemicelluloses, together with proteins, are capable of the Maillard reaction and may contribute to the overall secondary aroma of processed foodstuffs (Tomasik and Zawadzki, 1998). 

There are general reviews on heterocyclic syntheses by cycloaddition reactions of isocyanates and on the use of heterocyclic cations in preparative organic chemistry. More specific topics are 5-hydroxymethylfuran-2-carb-aldehyde, isobenzofurans and related ort/io-quinonoid systems, the conversion of 2//-cyclohepta[Zj] furan-2-one (1) into derivatives of azulene, the synthesis of indoles from o-alkylphenyl isocyanides, and abnormal Fischer indolization reactions of o-methoxyphenylhydrazones. Two reviews on isoindoles have appeared and a lecture on highly conducting charge-transfer complexes that are based on heterocyclic selenium and tellurium donors has been reprinted.Recent advances in the chemistry of imidazole and in the use of nitro-imidazoles as radiosensitizers have been summarized. There have been reviews on benzimidazole A -oxides and on dihydrobenzimidazoles, benzimidazolones, benzimidazolethiones, and related compounds. Other topics are synthetic applications of 1,3-dithiolium and 1,3-oxathiolium salts and of isoxazoles, the chemistry of benzisoxazoles, 2-amino-oxazoles, 5-oxazolones (2), furoxans, benzofuroxans, and related systems, the synthesis of five-membered meso-ionic compounds, and tetrazoles. ... 

A special case of an oxidation-reduction (redox) reaction catalysed typically by alkahs (in some cases the reaction also takes place in acidic solutions) is a Cannizzaro reaction. It occurs in aldehydes that do not have a hydrogen atom on the carbon, which means that the usual aldol condensation cannot take place. One molecule of aldehyde is oxidised with the simultaneous reduction of the second molecule and the reaction product is a mixture of acid and primary alcohol (Figure 4.68). A Cannizzaro reaction of formaldehyde yields formic acid and methanol furan-2-carbaldehyde gives rise to furan-2-carboxyHc acid (also known as 2-furoic acid or pyromucic acid) and 2-furfuryl alcohol (2-furyhnethanol or 2-hydroxymethylfuran). 

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