The Reactions of Carbohydrates

Polysaccharides are the most abundant constituents of living matter. They are in principle built up in the same manner as oligosaccharides. The chain molecules can be either linear or branched, a fact that markedly affects the physical properties of the polysaccharides. The carbohydrate material in plants is largely composed of cellulose and hemicelluloses. Chapter 3 deals with their structure and properties. 

Many reactions of wood polysaccharides (cellulose and hemicelluloses) are described in connection with pulping chemistry (Chapters 7 and 8). The following is therefore restricted to the most important and typical reactions. 

Uloses are derivatives of carbohydrates, which contain a further keto group. Aldosuloses are obtained from aldoses and diuloses from ketoses. They are important intermediates in the synthesis of carbohydrates. Uloses can be prepared by oxidation of derivatives in which all the hydroxyls except that one subjected to oxidation are blocked. Uloses are formed as intermediates during pulp bleaching (see Section 8.1.3). 

Periodic acid is a specific oxidant for any combination of hydroxyl, car- 

Aldoses and ketoses can be reduced to alditols by various agents for which purpose sodium borohydride is very useful. For industrial production of alditols, however, catalytic hydrogenation is applied. Only one product is formed from aldoses, whereas ketoses give rise to two diastereoisomers because of the generation of a new asymmetric center (Fig. 2-26). Sodium borohydride can also be used for reduction of carbonyl groups in polysaccharides. 

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Electron-transfer reactions occur all around us. Objects made of iron become coated with mst when they are exposed to moist air. Animals obtain energy from the reaction of carbohydrates with oxygen to form carbon dioxide and water. Turning on a flashlight generates a current of electricity from a chemical reaction in the batteries. In an aluminum refinery, huge quantities of electricity drive the conversion of aluminum oxide into aluminum metal. These different chemical processes share one common feature Each is an oxidation-reduction reaction, commonly called a redox reaction, in which electrons are transferred from one chemical species to another. 

The reaction of carbohydrates with sulfuryl chloride was first studied by Helferich and coworkers,68 70 and the work was extended by J. 

Cyclic thionocarbonates are formed under soliddiquid phase-transfer catalysed conditions from the reaction of diols with carbon disulphide [63]. The reaction has been specifically described for the reaction of carbohydrates, but should be generally applicable to all diols. 

Scheme 6 Mechanism of the reaction of carbohydrates with barbituric acids 30 or 31... 

Borrachero et al. (180) prepared a number of sugar isoxazolidines by the reaction of carbohydrate-functionalized nitrones with nitroalkenes (Scheme 1.33). They found a matched pair of chiral sugar cycloaddition reaction partners to be... 

The reaction of carbohydrate-derived imines with the Danishefsky diene, ( )-1 -methoxy-3-(trimethylsilyloxy)butadiene, to form heterocycles via the open-chain adducts (for assignment, see pp 456 and 478)130. 

The reaction of carbohydrates in alkaline or acidic aqueous solutions results in a myriad of products, many of which have been recognized for well over a century. The number of identified products has greatly increased in recent years, owing to the development of sophisticated techniques for separation and identification. With the exception of anhydro sugars and oligosaccharides, found as concentration-dependent, equilibrium constituents (reversion products) in acidic solutions, all of the products result from reactions of intermediates present in the Lobry de Bruyn-Alberda van Ekenstein transformation. 

There are many examples of the reaction of carbohydrates with Rydon reagents [16] the reaction is controlled by steric factors. Thus, no reaction occurred between 1,2-0-isopropylidene-5,6-di-0-methyl-a-D-glucofuranose and either 6 or bromotriphenoxyphos-phonium bromide, presumably because of the steric hindrance caused by the trioxabicyclo [3.3.0]octane ring-system, whereas methyl 2,5,6-tri-O-methyl-p-D-glucofuranoside reacted with 6 to give a 3-deoxy-3-iodo derivative in 31% yield. 

N. K. Kochetkov and A. I. Usov, The reaction of carbohydrates with triphenyl phosphite methiodide and related compounds. A new synthesis of deoxy sugars, Tetrahedron 79 973... 

The reactions of carbohydrate derivatives with certain organometallic reagents (Grignard and Friedel-Crafts processes) have been reviewed in this Series and elsewhere.87 The attempted application of a Chugaev reaction to sugar xanthates was reported by Wolfram and Foster.88 It was found,... 

The author hopes that the concepts presented here will stimulate further research and lead to a better understanding of the reactions of carbohydrates in alkaline solution. 

Method 2 (phenol-sulfuric acid reaction). The reaction of carbohydrates with phenol in the presence of sulfuric acid produces a UV-absorbing chromophore which is sufficiently sensitive to be used as a means of detecting less than 1-pg amounts of carbohydrates... 

The reaction of carbohydrates with ethylenediamine sulfate produces a stable fluorescence with excitation at 394 nm and emission at 470 nm. The reaction is specific for aldehydes and aliphatic polyhydroxyl compounds. It is used for the spray detection of carbohydrates separated by paper chromatography [109]. 

Methyl 4-0-(4-methoxybenzyl)2,3-di-0-methyl-oc-D-glucopyranoside has been prepared [371] by Liptak s procedure (see Sect. 2.6). This lithium aluminium hydride — aluminium trichloride method was also used in the synthesis of 4-hydroxy-3-methoxy-benzyl [372], 4-hydroxy-3,5-dimethoxybenzyl [372], and 1-phenylethyl [373] ethers from the 4,6-acetals derived from vanillin, syringealdehyde, and acetophenone. Various vinylbenzyl ethers were prepared by the reaction of carbohydrates with vinylbenzyl chloride, and copolymerized with styrene [374]. 

Predict the reactions of carbohydrates in acidic and basic solutions, and with oxidizing and reducing agents. 

Predict the reactions of carbohydrates in acidic and basic solutions, and with oxidizing and reducing agents. Predict the reactions that convert their hydroxyl groups to ethers or esters, and their carbonyl groups to acetals. Problems 23-56,57,58, G3, G4, G5, and 66... 

Malinen, R., and Sjostrom, E. (1972). Studies on the reactions of carbohydrates during oxygen bleaching. Part I. Oxidative alkaline degradation of cellobiose. Pap. Puu 54, 451 -468. 

The reaction of carbohydrates in acid or alkaline solution results in a number of products, many of which have been identified over the past century (L/i). With the exception of anhydrosugars (e.g., l,6-anhydro-/ -D-glucopyranose) and oligosaccharides, which are concentration-dependent and equilibrium components (reversion products) formed in acid solution, all of these products result from reactions associated with the Lobry de Bryn-Alberda Van Ekenstein transformation or intermediates formed from this transformation. 

An oxidation where this system is superior is in the reaction of carbohydrate derivatives where it is notably better than the acetic anhydride method, mainly due to the shorter reaction times, e.g. the preparation of the ketone (14 equation 7) ... 

Copper and rhodium complexes catalyze the reaction of alkenes with diazoacetate to give alkyl cyclopropanecarboxylates [13]. In the presence of Cu(acac)2, the reaction of carbohydrate enol ether 20 with methyl diazoacetate afforded a 1 4 mixture of cis- and frani-cyclopropanes 21 and 22 (c -product 21 was obtained with 95% de). When the reaction was catalyzed by CuOTf in the presence of hgand 23, the tranj -product 22 was obtained with 60% de (Scheme 10.4). The absolute configuration of the major diastereomer was not given [19]. 

As shown above, many of the methods that are available to form carbon-carbon bonds rely on the reaction of a carbanion with a suitable electrophile. Keto-sugars are readily available by simple oxidation of hydroxyl groups. Thus, the reaction of carbohydrate-derived ketones or aldehydes with carbanions has been extensively explored. However, keto groups are suitable substrates in olefinations, such as Wittig reactions, leading to versatile intermediates for the construction of complex structures. This section will detail some application of keto-sugars in total syntheses along these two main lines. 

Structure of Wood Components. As described in Chapter 2, wood consists of cellulose, hemicelluloses, lignin, and extractives. The first three are polymeric and are intimately associated with each other at the molecular level to form the cell wall. Carbohydrate content (cellulose and hemicelluloses) may reach 75% of the wood substance, so the reactions of carbohydrates are especially important. Although the extractives are extraneous materials, their presence can often influence reactions with the cell wall materials, and some wood properties also may be affected by reactions involving extractives. 

The reaction of carbohydrates with sulfuryl chloride can form chlorosulfate groups initially, followed by Sn2 displacement of the liberated chloride ion. This provides another effective method for the preparation of chlorodeoxy sugars [34,53]. Those positions, where the steric and polar factors are favorable for a Sn2 reaction, are more susceptible to displacement. The chlorosulfates that have been substituted with a chloride can easily be cleaved by treatment with sodium iodide. 

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