Sucrose reaction with sulfuric

Figure 14 shows another example of an elimination reaction one whose results can be seen easily. When sucrose reacts with concentrated sulfuric acid, water is eliminated, which leaves behind mostly carbon. Carbon is the black substance you can see forming in the photos and rising out of the beaker on the far right. 

The word carbohydrate hteraUy means hydrate of carbon. Carbohydrates have the general formula G (H20), in which x and y are whole numbers. However, even though the reaction of the carbohydrate sucrose with sulfuric acid produces carbon (Figure 15.4), this does not mean that sucrose is a... 

Sulfur functionalities can be also introduced on the sucrose skeleton. Activation of both terminal hydrojgil groups in 22 as mesylates and further reaction with sodium sulfide affords di-mercaptane 35 (Scheme 8). 

More drastic conditions were used with iodic acid, high temperatures and strongly acid solutions being employed. The oxidation products w ere not isolated. Williams and Woodsused 35% sulfuric acid containing 1% potassium iodate, the sugar being heated for ninety minutes at 100° with this oxidant. Ketoses, sucrose and pentoses were attacked, but L-rhamnose was oxidized more slowly. It was remarkable that none of the aldohexoses or lactose vere detectably oxidized. The reactions of cellobiose and trehalose were ascribed to impurities. 

For ethyl D-fructofuranoside, both anomers are formed in small proportion during the hydrogenolysis of sucrose in ethanol. When the reaction was performed at 100° in an atmosphere of argon, considerable quantities were obtained. Ethyl S-D-fructofuranoside, [ ]d —36° (in water), is readily hydrolyzed to D-fructose by invertase (and also by 0.1 N sulfuric acid) at room temperature. The same behavior was observed for a substance isolated from wheat germ. Acetylation yielded a sirupy product, but treatment with trityl chloride gave crystalline methyl 1,6-di-O-trityl-D-fructoside (m.p. 180-183°). With p-toluenesulfonyl chloride, a crystalline product is obtained, with m.p. 125-127°. Ethyl a-D-fructofuranoside ([ ]d +65°, in water) is not attacked by invertase. Tritylation, followed by acetylation, gives ethyl 3,4-di-O-acetyl-l, 6-di-O-trityl-ai-D-fructofuran-oside m.p., 142-144° and [q ]d +44.5° (in chloroform). 

Another example of an elimination reaction is the dehydration of sucrose with concentrated sulfuric acid, shown in Figure 4.2. 

Sodium iV-cyclohexyl sulfamate (cycliunate, 141 R = cyclohexyl) was introduced as a non-nutritive artificial sweetener in 1939. It is 30 times sweeter than sucrose, but was banned in the USA and Canada in 1970 because rats fed with large doses developed bladder cancer, although it is permitted in many other countries. Cyclohexylammonium sulfamate, an intermediate in the manufacture of non-nutritive sweeteners, may be prepared by reaction of cyclohexylamine (two to three equivalents) with chlorosulfonic acid in trichloroethene at 60-75 C the presence of the excess amine avoids an acidic medium and side reactions. A-Cyclohexylsulfamic acid has been obtained by treatment of cyclohexylamine with a mixture of sulfur trioxide and chlorosulfonic acid in trichloroethene at < 60 Cyclamate can also be manufactured by heating cyclohexylamine with sulfamic acid in xylene at 132-139 Benson and Spillane discussed the... 

The degradation of carbohydrates by strong acids has been recognized for many years. It was a common elementary school demonstration to add sulfuric acid to sugar (sucrose) to produce carbon. Under more controlled conditions, the reaction of all carbohydrates in aqueous solution with strong acid has been shown to produce the formation of a derivative of furfural as the major product [7]. 

Concentrated sulfuric acid has some distinctive properties. It has a very strong affinity for water, strong enough that it will even remove H and O atoms (in the proportion H2O) from some compounds. In the reaction of concentrated sulfuric acid with a carbohydrate such as sucrose, all the H and O atoms are removed and a residue of pure carbon is left, as shown in the photo on the next page. The chemical equation for the reaction that occurs is given below ... 

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