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( Sucrose)
186&_160;°C Pure sucrose is most often prepared as a fine, white, odorless crystalline powder with a pleasing, sweet taste; the common table sugar. Large crystals are sometimes grown from aqueous solutions of sucrose on a string (or other nucleation surface) to form rock candy, a confection. Like other carbohydrates, sucrose has a hydrogen to oxygen ratio of 21. It consists of two monosaccharides, a-glucose and fructose, joined by a glycosidic bond between carbon atom 1 of the glucose unit and carbon atom 2 of the fructose unit. What is notable about sucrose is that unlike most polysaccharides, the glycosidic bond is formed between the reducing ends of both glucose and fructose, and not between the reducing end of one and the nonreducing end of the other. The effect of this inhibits further bonding to other saccharide units. Since it contains no free anomeric carbon atom, it is classified as a nonreducing sugar. Sucrose melts and decomposes at 186 °C to form caramel, and when combusted produces carbon, carbon dioxide, and water. Water breaks down sucrose by hydrolysis, however the process is so gradual that it could sit in solution for years with negligible change. If the enzyme sucrase is added however, the reaction will proceed rapidly. Reacting sucrose with sulfuric acid dehydrates the sucrose and forms the element carbon, as demonstrated in the following equation
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