Reduction of D-fructose

Another name for glucitol obtained by reduction of d glucose is sorbitol it is used as a sweetener especially in special diets required to be low in sugar Reduction of D fructose yields a mixture of glucitol and mannitol corresponding to the two possi ble configurations at the newly generated chirality center at C 2... 

Reduction. Mono- and oligosaccharides can be reduced to polyols (polyhydroxy alcohols) termed alditols (glycitols) (1) (see Sugaralcohols). Common examples of compounds in this class are D-glucitol (sorbitol) [50-70-4] made by reduction of D-glucose and xyhtol [87-99-0] made from D-xylose. Glycerol [56-87-5] is also an alditol. Reduction of D-fructose produces a mixture of D-glucitol and D-mannitol [69-65-8]. 

First, it is important to stress that asymmetric chemical transformations are not a recent invention on the contrary, we are now well past the 100th anniversary of tlie first reported case in the literature by Emil Fischer who in 1889-1890 found that HCN addition to r-arabinose produced two epimeric carbohydrate acids after hydrolysis [1]. Soon after, a second example [2] - NaHg [sodium amalgam] reduction of D-fructose - was published, together with some thoughts on the fundamental importance of these observations for the future. In the first decade of the new century McKenzie et al. published a series of papers titled Studies in Asymmetric Synthesis , a phrase which, thus, was by no means created only in the re-... 

Problem 18.19. The carbonyl group of a monosaccharide can be reduced to an alcohol group by various reducing agents, e.g., H2 in the presence of a metal catalyst or NaBH4 (Sec. 14.6). Show the product(s) of the reduction of D-fructose by NaBH4. 

The reduction of D-fructose by NaBH4 gives two alditols, one of which is D-sorbitol. Name and draw a structural formula for the other alditol. (See Example 17.6)... 

Reduction of D-fructose with NaBH4 gives a mixture of o-glucitol and o-mannitol. What does this result prove about the configurations of D-fructose, D-mannose, and D-glucose ... 

Name the two alditols formed by NaBH reduction of D-fructose. 

The reduction of ketoses yields both C-2 komers. For example, the reduction of D-g/ycero-tetrulose creates erythritol and d-threitol. Reduction of D-fructose yields D-glucitol and D-mannitol. 

Reduction of D-fructose with sodium borohydride yields a mixture of two alditols. Explain why. Name the two alditols. 

Fischer1-2 decided that the mode of formation, the reactions with hydrazines, aromatic diamines, and oxidizing agents, and the reduction to D-fructose could be explained by attributing to the open-chain form of D-glucosone the a-ketoaldehyde structure L. 

The separation of mixtures of hexitols has long been a difficult problem. The removal of sorbitol from L-iditol by bacterial action is a classical example. Destruction of one component as a means of separation is drastic and is applicable to only a few mixtures. Even from an analytical point of view, separation has been difficult. The proportions of D-mannitol and sorbitol in the reduction products of D-fructose may be determined approximately by crystallizing and weighing the D-mannitol, but the amount of D-mannitol still in solution remains an unknown quantity. 

D,L-Mannitol has been obtained by sodium amalgam reduction of D,L-mannose. The identical hexitol is formed from the formaldehyde polymer, acrose, by conversion through its osazone and osone to D,L-fructose (a-acrose) followed by reduction (83). 

Note that the configurations are identical at C-3, C-4, and C-5. The fact that D-fructose gives both of these polyols on reduction tells us that it must also have the same configuration as they do at C-3, C-4, and C-5. Thus, the keto group of D-fructose must be at C-2. 

Attempts by Smith and ToUens " to oxidize n-fructose with bromine by the method of Clowes and Tollens were unsuccessful a double compound of D-fructose and calcium bromide was obtained. No yield of this product was given. The reaction mixture of D-fructose, calcium carbonate, water and bromine was shaken until all the bromine had dissolved, after which the double compound was separated from the concentrated solution. The calcium bromide was formed from the interaction of calcium carbonate with hydrogen bromide in the reaction solution. The hydrogen bromide could be formed in two ways by the hydrolysis of bromine in water (reaction 1, page 134) or by the reduction of bromine during the oxidation of D-fructose. The former is the more probable explanation, but a blank run without the ketose was not attempted. 

General directions for reduction of D-glucose, D-mannose, D-galactose, L-arabinose, D-xylose, and D-fructose ... 

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