D-Glucose production

A solution of the starting 2,4-bis-thionocarbonate [Eq. (15)] 37 (174 mg, 0.40 mmol), chlorotrimethylsilane (0.31 mL, 2.4 mmol), and triethylamine (0.5 mL, 3.6 mmol) in benzene (3 mL) was stirred for 1 h at room temperature. After filtration, the solvent was evaporated. The residue was dissolved in toluene (1 mL) and diphenylsilane (294 p,L, 1.6 mmol) was added. The reaction mixture was heated to reflux and treated under argon with 150 mL portions of an AIBN solution (262 mg of AIBN in 3 mL of dioxane) five times (at 20 min intervals) under reflux. After evaporation of the solvent under reduced pressure, the residue was analyzed by H NMR to give 85% of the 2,4-dideoxy-3-trimethylsilyl-l,6-anhydro-D-glucose product 38. 

As crystalline D-glucose products are now manufactured almost exclusively from starch hydrolyzates made by enzymically catalyzed hydrolysis instead of by acid-catalyzed hydrolysis, discussion of crystalline D-glucose technology is presented under the part of this Chapter dealing with enzyme-based technologies. 

The main raw material required for the production of viscose is ceUulose (qv), a natural polymer of D-glucose (Fig. 1). The repeating monomer unit is a pair of anhydroglucose units (AGU). CeUulose and starch (qv) are identical but for the way in which the ring oxygen atoms alternate from side to side of the polymer chain (beta linkages) in ceUulose, but remain on the same side (alpha linkages) in starch. 

Depolymerization of starch in alkaline solution proceeds more slowly than in acid and produces isosaccharinic acid derivatives rather than D-glucose as a major product. The mechanism involves a -elimination-type reaction (48). 

Commercial starch is mainly com starch, but smaller amounts of sorghum, wheat, and potato starch are also produced. In 1992, 1303 million bushels (45.8 X 10 m ) of com were ground for starch and other products (120) 1 m com weighs - 721 kg and yields 438 kg starch, 26 kg oil, and 142 kg combined gluten and hulls. In the United States in 1994—1995, 462 million bushels were used to produce high fmctose com symp, 231 million bushels went to produce D-glucose, 533 million bushels were used for alcohol production, and 247 million bushels were converted to starch (121). 

Commercial dextrose products are produced in both dry and symp forms. Dry products are prepared by crysta11i2ation (qv) to either an anhydrous, DHnO, or hydrated, H20, form. These include dextrose hydrate [16824-90-17, anhydrous a-D-glucose [26655-34-5] (1), and anhydrous... 

P-D-glucose [28905-12-6] (2). Symp products are produced that contain from 95 to over 99% dextrose. 

Fig. 2. Production of crystalline dextrose (7), where ds is dry substance db, dry basis Dg, D-glucose and CPY, crystal-phase yield.

Most current industrial vitamin C production is based on the efficient second synthesis developed by Reichstein and Grbssner in 1934 (15). Various attempts to develop a superior, more economical L-ascorbic acid process have been reported since 1934. These approaches, which have met with htde success, ate summarized in Crawford s comprehensive review (46). Currently, all chemical syntheses of vitamin C involve modifications of the Reichstein and Grbssner approach (Fig. 5). In the first step, D-glucose (4) is catalytically (Ni-catalyst) hydrogenated to D-sorbitol (20). Oxidation to L-sotbose (21) occurs microhiologicaRy with The isolated L-sotbose is reacted with acetone and sulfuric acid to yield 2,3 4,6 diacetone-L-sorbose,... 

The catalytic hydrogenation of D-glucose to D-sorbitol is carried out at elevated temperature and pressure with hydrogen ia the preseace of nickel catalysts, in both batch and continuous operations, with >97% yield (56,57). The cathodic reduction of D-glucose to L-sorbitol has been practiced (58). D-Mannitol is a by-product (59). 

Oligo- and higher saccharides are produced extensively by acid-and/or enzyme-catalyzed hydrolysis of starch, generally in the form of symps of mixtures (12). These products are classified by thek dextrose equivalency (DE), which is an indication of thek molecular size and is a measure of thek reducing power with the DE value of anhydrous D-glucose defined as 100. 

The total yield amounts to 260-266 g. (48.5-49.5 per cent of the theoretical amount). The product is contaminated by slight traces of d-glucose and possesses a very faint reducing power towards Fehling s solution. For complete purification it is recrystallized (with practically no loss and practically no change in melting point) from five parts of methyl alcohol with the use, if necessary, of decolorizing carbon. 

As a final example we consider noncovalent molecular complex formation with the macrocyclic ligand a-cyclodextrin, a natural product consisting of six a-D-glucose units linked 1-4 to form a torus whose cavity is capable of including molecules the size of an aromatic ring. Table 4-3 gives some rate constants for this reaction, where L represents the cyclodextrin and S is the substrate ... 

Liver contains an enzyme called glucokinase, which also carries out the reaction in Figure 19.4 but is highly specific for D-glucose, has a much higher for glucose (approximately 10.0 mAf), and is not product-inhibited. With such... 

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