Dehydration of sugar

The odor of isomaltol is described as sweet, but with a burnt sugar and fruity character (H) 2-Acetylfuran and 2-hydroxyacetylfuran impart burnt sweetish flavors. Furfuryl alcohol and 5-methyl-2-furaldehyde have sweet caramellic flavors (31). The major formation route to most furans in heated-abused citrus products has been postulated as acid-catalyzed enolizations and dehydrations of sugars (38). Furans, such as 2-hydroxyacetylfuran and isomaltol... 

Acid-catalyzed reversion presents a complicated process. D-Glucose gives rise to oligosaccharides, whereas o-fructose only dimerizes. " Both reactions are reversible, but seem to contribute to the complexity of carameliza-tion in an acidic medium. Reversion products, as well as D- ucose and D-fructose themselves, react with 5-(hydroxymethyl)-2-furaldehyde, and these reactions seem to be the source of the high-molecular-weight fraction of caramel. The process is sensitive to the nature of the acid by virtue of its effect upon the competing dehydration of sugars, namely, the rehydration of... 

Metal salts [among them, chlorides of aluminum, chromium(III), and lanthanum] accelerate both the dehydration of sugars and the rehydration of... 

Lignins Aromatic polymers formed by the irreversible dehydration of sugars. Because of their structure, they cannot be broken down by the digestive enzymes and make up part of the stool bulk. 

Lignins are formed by the irreversible dehydration of sugars that result in aromatic structures. The remaining alcohol or phenol OH groups can react with each other and with aldehyde and ketone groups to form polymers. An example... 

Figure 25-2. A lignin molecule in an early stage of condensation. The aromatic rings are a result of irreversible dehydration of sugar residues.

Kinetics is the study of fhe rate of chemical reacfions, such as the acid dehydration of sugar, shown in this photograph. 

Figure 4.5 Acid-catalysed dehydration of sugars to furans.

Iodomethyl)furfural (IMF) has been prepared as an intermediate by Finkelstein reaction of CMF with Nal in acetone, although attempts to isolate it have not been successful [114]. In 2012, Sen et al. reported the hydroiodic acid-catalyzed dehydration of sugars during which in situ generated IMF was reduced to 5-methylfurfural... 

Fig. 11 Side products in the sucrose-to-lactate (green) convta ion in MeOH and their raigin blue retro-aldol of glucose (see Sect. 7) red methanolysis of sucrose ot acetalizatirai of glucose black dehydration of sugars to HMF, furan ethers and humins. MMHB methyl methoxy-2-hydroxybutanoate, MVG methyl vinyl glycolate, MHB methyl-2-hydroxybutanoate, GADMA glycolaldehyde dimethyl acetal. HG = hydrogenation...

Tang, Z., Cenkowsld, S., Muir, W. E., 2000. Dehydration of sugar-beet pulp in superheated steam and hot air. Trans. ASAE 43 685-689. 

The world s 140 million metric tons of annual ethylene capacity almost exclusively employs steam cracking of hydrocarbon feedstocks [5]. The majority of the feedstocks come from petroleum refining, such as by cracking of naphtha, but some producers use liquefied natural gas as a feedstock. In Brazil, where sugar cane is plentiful, Braskem has built a 200,000 metric ton per year ethylene plant based upon the dehydration of sugar-derived ethanol [6]. In the United States, natural gas liquids, a mixture of ethane, propane, butane, and other hydrocarbons, are available from shale deposits. The ethane is separated and cracked to make ethylene. Depending on the cost of oil and natural gas, this can be an economic advantage. In 2012, about 70% of United States ethylene production was from ethane [7]. 

Sugars (hexoses) yield formic acid as a product of the Cannizzaro reaction of formaldehyde and as one of the final products of the dehydration of sugars in addic media and their degradation in neutral and alkaHne media. At high concentrations (in quantities of up to 2%), formic add therefore occurs in acid protein hydrolysates, where it is formed by 5-hydroxymethyl-2-furancarbaldehyde degradation. In randd fats, formic acid arises by oxidative decomposition of aldehydes. Formic acid is sometimes used as a preservative. 

Other amorphous carbons include carbon fibers such as M-46, which are manufactured by heat-treatment at low temperature, carbon materials made by dehydration of sugar with concentrated sulfuric acid, ribbon-like carbon... 

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