Sucrose (also called saccharose) is a disaccharide, a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula C12H22O11. For human consumption, sucrose is extracted and refined from either sugarcane or sugar beet. Sugar mills – typically located in tropical regions near where sugarcane is grown – crush the cane and produce raw sugar which is shipped to other factories for refining into pure sucrose. Sugar beet factories are located in temperate climates where the beet is grown, and process the beets directly into refined sugar. The sugar-refining process involves washing the raw sugar crystals before dissolving them into a sugar syrup which is filtered and then passed over carbon to remove any residual colour. The sugar syrup is then concentrated by boiling under a vacuum and crystallized as the final purification process to produce crystals of pure sucrose that are clear, odorless, and sweet. Sugar is often an added ingredient in food production and recipes. About 185 million tonnes of sugar were produced worldwide in 2017.
Etymology The word sucrose was coined in 1857, by the English chemist William Miller from the French sucre ("sugar") and the generic chemical suffix for sugars -ose. The abbreviated term Suc is often used for sucrose in scientific literature. The name saccharose was coined in 1860 by the French chemist Marcellin Berthelot. Saccharose is an obsolete name for sugars in general, especially sucrose.
Physical and chemical properties
Structure Sucrose's IUPAC name is β-D-fructofuranosyl-(2→1)-α-D-glucopyranoside. In this disaccharide, glucose and fructose are linked via a glycosidic linkage, i.e. an ether bond between C1 on the glucosyl subunit and C2 on the fructosyl unit. Glucose exists predominantly as a mixture of α and β "pyranose" anomers, but sucrose has only the α form. Fructose exists as a mixture of five tautomers but sucrose has only the β-D-fructofuranose form. Unlike most disaccharides, the glycosidic bond in sucrose is formed between the reducing ends of both glucose and fructose, and not between the reducing end of one and the non-reducing end of the other. This linkage inhibits further bonding to other saccharide units, and prevents sucrose from spontaneously reacting with cellular and circulatory macromolecules in the manner that glucose and other reducing sugars do. Since sucrose contains no anomeric hydroxyl groups, it is classified as a non-reducing sugar. Sucrose crystallizes in the monoclinic space group P21 with room-temperature lattice parameters a = 1.08631 nm, b = 0.87044 nm, c = 0.77624 nm, β = 102.938°.
Thermal and oxidative degradation Pure crystalline sucrose melts at approximately 189 °C (372 °F). However, the melting point is highly sensitive to the presence of water and impurities such as mineral salts, and sucrose also begins to decompose at a lower temperature than its melting point. The decomposition of sucrose is exploited in cookery to form caramel. Like other carbohydrates, sucrose combusts to carbon dioxide and water by the simplified equation:
C12H22O11 + 12 O2 → 12 CO2 + 11 H2O Mixing sucrose with the oxidizer potassium nitrate produces a fuel called rocket candy that is often used to propel amateur rocket motors. C12H22O11 + 6 KNO3 → 9 CO + 3 N2 + 11 H2O + 3 K2CO3 This reaction is somewhat simplified though. Some of the carbon does get fully oxidized to carbon dioxide, and other reactions, such as the water-gas shift reaction also take place. A more accurate theoretical equation is: C12H22O11 + 6.288 KNO3 → 3.796 CO2 + 5.205 CO + 7.794 H2O + 3.065 H2 + 3.143 N2 + 2.988 K2CO3 + 0.274 KOH Sucrose burns with chloric acid, formed by the reaction of hydrochloric acid and potassium chlorate: 8 HClO3 + C12H22O11 → 11 H2O + 12 CO2 + 8 HCl Sucrose can be dehydrated with concentrated sulfuric acid to form a black, carbon-rich solid, as indicated in the following idealized equation: H2SO4 (catalyst) + C12H22O11 → 12 C + 11 H2O + heat (and some H2O + SO3 as a result of the heat). The formula for sucrose's decomposition can be represented as a two-step reaction: the first simplified reaction is dehydration of sucrose to pure carbon and water, and then carbon is oxidised to CO2 by O2 from air. C12H22O11 + heat → 12 C + 11 H2O 12 C + 12 O2 → 12 CO2
Hydrolysis Hydrolysis breaks the glycosidic bond converting sucrose into glucose and fructose. Hydrolysis is, however, so slow that solutions of sucrose can sit for years with negligible change. If the enzyme sucrase is added, however, the reaction will proceed rapidly. Hydrolysis can also be accelerated with acids, such as cream of tartar or lemon juice, both weak acids. Likewise, gastric acidity converts sucrose to glucose and fructose during digestion, the bond between them being an acetal bond which can be broken by an acid. Given (higher) heats of combustion of 1349.6 kcal/mol for sucrose, 673.0 for glucose, and 675.6 for fructose, hydrolysis releases about 1.0 kcal (4.2 kJ) per mole of sucrose, or about 3 small calories per gram of product.
Synthesis and biosynthesis of sucrose The biosynthesis of sucrose proceeds via the precursors UDP-glucose and fructose 6-phosphate, catalyzed by the enzyme sucrose-6-phosphate synthase. The energy for the reaction is gained by the cleavage of uridine diphosphate (UDP). Sucrose is formed by plants, algae and cyanobacteria but not by other organisms. Sucrose is the end product of photosynthesis and is found naturally in many food plants along with the monosaccharide fructose. In many fruits, such as pineapple and apricot, sucrose is the main sugar. In others, such as grapes and pears, fructose is the main sugar.
Chemical synthesis After numerous unsuccessful attempts by others, Raymond Lemieux and George Huber succeeded in synthesizing sucrose from acetylated glucose and fructose in 1953.
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