Why is concentrated sulfuric acid syrupy

Cane sugar
Beet sugar
Sucrose occurs in many plants, but especially in fruits and plant juices. Sugar beet and sugar cane are the most important sources of raw materials.
Sucrose forms pure white, sweet-tasting crystals that are very soluble in water. The carbohydrate belongs to the family of disaccharides or disaccharides. White sucrose is also known in households as “cane sugar”. In the case of sugar production from sugar cane, this means the unpurified, still slightly yellowish sugar:

Above 160 ° C, sucrose decomposes with a brown color and forms caramel, which contains characteristic aromatic substances and decomposition products such as maltol. The aqueous solution of the caramel is called "sugar liqueur". It is used to color food, for example beer, rum, liqueur or candy. Concentrated sulfuric acid dehydrates sucrose and pure carbon is formed:

Sucrose does not have a reducing effect, the Fehling's test is negative. Acids such as dilute hydrochloric acid split the double sugar into the single sugars fructose and glucose. During digestion, this process takes place with the help of the enzyme invertase. A double sugar (disaccharide) is broken down into a single sugar (monosaccharide).


One double sugar molecule (left) and two single sugar molecules (right)

Frequent sugar consumption is responsible for tooth decay. Saliva and degradation products from food form a plaque, which provides an optimal breeding ground for oral bacteria. These convert the sugar into organic acids that attack the tooth enamel and, in an advanced stage, also the soft dentin underneath. After every sugar intake, the acid production of the plaque bacteria increases many times over. Frequent tooth brushing only removes plaque, but it doesn't address the real problem. Excessive carbohydrate consumption can also lead to obesity. Excess sugar is converted into fat in the body, which is stored as reserve material in the tissue.
The sugar beet grows in Central Europe. It is a biennial plant that builds up a supply of sugar in the first year, which is used as food in the second year of the flowering plant. The beet contains 17 to 20 percent sugar. Sugar is obtained from pulp of the sugar beet, which is extracted with water.

Sugar beet

Calcium oxide is then added to the extract in order to precipitate the vegetable acids such as oxalic acid or tartaric acid and the proteins. The excess lime is excreted through the introduction of carbon dioxide. The subsequent evaporation of the water from the sugar solution in vacuo gives a syrupy solution. The cane sugar that crystallizes out is separated from the brown syrup that remains by centrifugation. The residue, the molasses, is used as fodder or is used for alcoholic fermentation. The cane sugar is purified, or refined, by recrystallization, filtration and evaporation in vacuo. This is how you get the white fine sugar, which consists mainly of sucrose. Over 100 million tons of sucrose are produced worldwide every year, one third of which comes from sugar beet and two thirds from sugar cane.

Sugar cane
Sucrose is widely used in food preparation. Fine sugar is the white sugar that has been purified by refining. The brownish cane sugar still contains syrup residues. Caramel is a brownish decomposition product of sugar. Sucrose is used in the chemical industry for the synthesis of many other chemical compounds, for example for the production of ethanol, glycerine, detergents, plastics, explosives and alternative fuels.

Further information

Carbohydrates in the organic dictionary