General reactions of the sugars

10 drops of water, and add 2 drops of a 10 per cent solution of a-naphthol in chloroform. Allow 1 cc. of pure concentrated sulphuric acid to flow, from a pipette, down the side of the inclined tube so that two layers are formed. A pipette for this purpose may be made by drawing out a piece of glass tubing to a fine opening at one end. Observe what happens in a few seconds. Shake and allow the mixture to stand 2 minutes note the color, Dilute with water, note the change, add an excess of ammonia, and note the color. 

Properties of Sucrose (SECTIONS 366, 368).—(a) Preparation of caramel.—Place about 2 grams of sucrose in a test-tube and heat it for 15 minutes in an oil-bath at 210°. Taste the product and determine if it is soluble in water. 

—The procedure adopted in this experiment is designed to bring about the precipitation of the proteins the milk contains. The solution is heated with calcium carbonate before evaporation in order to neutralise the fine acid present, and thus largely prevent the hydrolysis of lactose which takes place when the sugar is heated with water in the presence of acids. 

Oxidation of Lactose (see galactose, SECTIONS 359 and 319).—Heat 10 grams of lactose on the water-bath with about four times its weight of concentrated nitric acid (28 cc.) until the brown oxide of nitrogen is formed. Keep the mixture at 70°-80° until the evolution of gas ceases. Dilute the solution with one-half its bulk of water and let it stand until cold, mucic and oxalic acids crystallize out. Filter, save the filtrate, and wash the crystals with warm alcohol to dissolve the oxalic acid, and then twice with a small amount of cold water. Recrystallize the residue, mucic acid, from a small amount of boiling water. 

Neutralize the filtrate obtained above with solid potassium carbonate, strongly acidify with glacial acetic acid, and let stand until crystals of potassium hydrogen saccharate are formed. Filter these off and recrystallize them from the smallest possible amount of boiling water. 

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Occurrence and General Reactions of the Sugars of the Cardiac Glycosides. 148... 

Reactions of the sugar with the alcohol group of the solvent are confined to glycoside formation, a reaction catalyzed by acids ranging from mineral acids to insoluble ion-exchangers.114-116 A general review by Shafizadeh117 describes the earlier work. Bishop and cowork-... 

The mildest type of reaction of the sugars induced by acids is the interconversion between a- and /3-isomers or between ring isomers. This type of change has been discussed above under the general subject of mutarotation. Dilute acids at room temperatures have little or no additional action on the sugars, but hot concentrated acids produce profound changes. 

The nitromethane synthesis of higher-carbon aldose sugars utilizes two well-known general reactions of the nitroparaflBns. These are the base-catalyzed condensation of nitromethane with an aldehyde to produce a C-ni-troalcohol (146), and the decomposition of the sodium salt of the latter with cold, moderately concentrated mineral acid to produce an aldehyde (147) containing one more carbon atom than the original aldehyde. 

In carbohydrate chemistry, the preparation of ethers that are stable in the presence of acids, bases, and aqueous alkali is an important analytical and synthetic tool. The methods used for the etherification of hydroxyl groups51 generally employ reactions of unprotected sugars and glycosides with methyl, allyl, benzyl, triphenylmethyl, and alkylsilyl halides in the presence of a variety of aqueous and nonaqueous bases. 

Sugars are reactive molecules. Their reaction with amines, R—NH2, is of particular importance to us. Proteins possess a number of amino groups, one at the N-terminus of the protein and one for each lysine residue in the protein. There is a lot of sugar floating around in the human body. So it should not surprise us that there is nonspecific reaction of these sugars with proteins. These reactions are generally slow but they do occur sufficiently fast to be important. 

The general usefulness of the developed methodology can be verified also in different areas. Thus chemoselec-tive reactions could be also carried out with p-unsubsti-tuted a-phenylthio substituted a, p-unsaturated carbonyl compounds and enol ethers as outlined in Scheme 6 (21). Naturally occuring 2,3,6-trideoxy and 4-amino-2,3,4,6-tetradeoxy sugars are obtained quite readily from this methodology. 

The C-glycosylation procedures generally exploit the electrophilic character of the anomeric carbon of the sugar. The new C-C bond can be formed by reaction of the aldehydic function of the sugar with an organometallic or a Wittig... 

FIGURE 20-11 Transketolase-catalyzed reactions of the Calvin cycle, (a) General reaction catalyzed by transketolase the transfer of a two-carbon group, carried temporarily on enzyme-bound TPP, from a ketose donor to an aldose acceptor, (b) Conversion of a hexose and a triose to a four-carbon and a five-carbon sugar (step of Fig. 20-10). (c) Conversion of seven-carbon and three-carbon sugars to two pentoses (step of Fig. 20-10). 

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