Sugars furfural

Furanose rings 161,175. See also Sugars Furfural 251,167s... 

Organic reactions, mainly those that require free water, can also be controlled by the ratio of free and bound water in the microreactor of the reaction (the core of the microemulsion). Maillard reactions between amino acids (cysteine) and sugars (furfural) can be manipulated by the core water to improve the selectivity of products and the rates of reactions [92]. 

Molisch s test A general test for carbohydrates. The carbohydrate is dissolved in water, alcoholic 1-naphthol added, and concentrated sulphuric acid poured down the side of the tube. A deep violet ring is formed at the junction of the liquids. A modification, the rapid furfural test , is used to distinguish between glucose and fructose. A mixture of the sugar, 1-naphthol, and concentrated hydrochloric acid is boiled. With fructose and saccharides containing fructose a violet colour is produced immediately the solution boils. With glucose the appearance of the colour is slower. 

Furfural is derived from biomass by a process in which the hemiceUulose fraction is broken down into monomeric 5-carbon sugar units which then are dehydrated to form furfural. 

Sugar is destroyed by pH extremes, and inadequate pH control can cause significant sucrose losses in sugar mills. Sucrose is one of the most acid-labile disaccharides known (27), and its hydrolysis to invert is readily catalyzed by heat and low pH prolonged exposure converts the monosaccharides to hydroxymethyl furfural, which has appHcations for synthesis of glycols, ethers, polymers, and pharmaceuticals (16,30). The molecular mechanism that occurs during acid hydrolysis operates, albeit slowly, as high as pH 8.5 (18). 

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. 

In the acid hydrolysis process (79—81), wood is treated with concentrated or dilute acid solution to produce a lignin-rich residue and a Hquor containing sugars, organic acids, furfural, and other chemicals. The process is adaptable to all species and all forms of wood waste. The Hquor can be concentrated to a molasses for animal feed (82), used as a substrate for fermentation to ethanol or yeast (82), or dehydrated to furfural and levulinic acid (83—86). Attempts have been made to obtain marketable products from the lignin residue (87) rather than using it as a fuel, but currently only carbohydrate-derived products appear practical. 

Although the hydrolysis of wood to produce simple sugars has not proved to be economically feasible, by-product sugars from sulfite pulping are used to produce ethanol and to feed yeast (107). Furthermore, a hemiceUulose molasses, obtained as a by-product in hardboard manufacture, can be used in catde feeds instead of blackstrap molasses (108). Furfural can be produced from a variety of wood processing byproducts, such as spent sulfite Hquor, bquors from the prehydrolysis of wood for kraft pulping, hardboard plants, and hardwood wastes (109). 

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 injected fluids include the effluent from a sugar mill and the waste from the production of furfural, an aldehyde processed from the residues of processed sugar cane. The waste is hot (about 75°C to 93°C), acidic (pH 2.6 to 4.5), and has high concentrations of organics, nitrogen, and phosphorus.173 The waste is not classified as hazardous under 40 CFR 261, and the well is currently regulated by the State of Florida as a nonhazardous injection well. The organic carbon concentration exceeds 5000 mg/L. 

Hydrolysis products of neomycin may be an amino-sugar, a pentose or furfural depending on the reaction conditions chosen. Each of these entities has been utilised for indirect spectrophotometric determination of neomycin. 

In some cases, the hydrolysis reaction liberates the sugars from the biomass and converts them directly into derivatives such as furfural, hydroxymethyl furfural and/or levulinic acid. These derivatives can be further converted into various chemical intermediates. We will not discuss these further conversions as they are extensively reported in the literature, e.g., for furfural [15, 44], hydroxymethyl furfural [15, 44, 50] and levulinic acid [15, 44-47]. 

Like D-glucose and D-fructose, however, D-xylose can be utilized chemic ly or microbially—to generate a variety of interesting five-ca n c emica s o er than furfural (vide supra) or xylitol, a noncaloric sweetener, both being duectly produced from xylan hydrolysates, that is, without the actual isolation of the sugar. Other readily accessible intermediate products of high preparative utiUty (Scheme 2.14) are the open-chain fixed dithioacetal, the D-xylal, and D-hydroxy-xylal esters, or pyrazol or imidazol A -heterocycles with a hydrophilic trihydroxypropyl side chain. 

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