Sulfur dioxide (chemical formula SO2) is the most common, simplest, and irritating sulfur oxide. One of the major air pollutants. The gas is ejected during volcanic eruptions, and sulfur dioxide is also produced in many industrial processes. Since coal and oil usually contain elemental sulfur, sulfur dioxide is formed when burned. When sulfur dioxide dissolves in water, sulfurous acid is formed. If sulfurous acid is further oxidized in the presence of PM2.5, sulfuric acid (the main component of acid rain) will be formed quickly and efficiently. This is one reason for concern about the environmental effects of using these fuels as energy sources.
On October 27, 2017, the list of carcinogens published by the World Health Organization's International Agency for Research on Cancer was preliminarily sorted for reference, and sulfur dioxide was included in the list of three types of carcinogens.
SO2 specification
Chinese name: sulfur dioxide
Alias: Sulfurous Anhydride
English name: Sulfur dioxide
Chemical formula: SO2
CAS number: 7446-09-5
RTECS: WS4550000
Molar mass: 64.054 g mol?1
Appearance: colorless gas
Density: 0.002551 g/L
Melting point: -72.4℃
Boiling point: -10℃
Solubility (water): 9.4 g/100 mL (25 °C)
Warning term: R: 23-34
Safety Terms: S: 1/2-9-26-36/37/39-45
Main hazards: one of the main pollutants in the atmosphere
Application：
In addition to being mainly used for the production of sulfuric acid, other important uses of sulfur dioxide include: production of sulfite pulp in the paper industry; manufacture of various sulfites, bisulfites, thiosulfates; production of nylon (nylon 6) monomers, Organic compounds such as synthetic detergents and rubber accelerators; also used in the pharmaceutical industry. Sulfur dioxide can also be used as a bleaching agent for fabrics and leather; as a fumigant in agriculture; as a preservative and disinfectant in the food industry. Liquid sulfur dioxide is a good solvent for some organic substances and is used in the refining of mineral oils.
Sulfur dioxide has bleaching and antiseptic effects on food. The use of sulfur dioxide can achieve the effect of brightening and whitening the appearance of products. It is a commonly used bleaching agent and preservative in food processing, but it must be used in strict accordance with the relevant national scope and standards. Otherwise, it will affect the human body. healthy.
Winemaking
Sulfur dioxide is a very useful compound in winemaking, its E code is E220. It's even found in so-called "sulfur-free" wines in concentrations of up to 10 mg per liter. It acts as an antibiotic and antioxidant, preventing the wine from being damaged and oxidized by bacteria. It also helps keep volatile acidity at the desired level. The reason why wine labels have words such as "contains sulfites" is because of sulfur dioxide. Under US and EU law, a wine does not need to be labeled "contains sulfites" if its SO2 concentration is less than 10ppm. The upper limit of SO2 concentration allowed in wine is 350ppm in the US, while in the EU it is 160ppm for red wine and 210ppm for white wine. If the concentration of SO2 is very low, it is difficult to detect, but when the concentration is greater than 50ppm, the smell of SO2 can be smelled with the nose and tasted with the tongue.
Reducing bleach
SO2 is also a good reducing agent. In the presence of water, sulfur dioxide can discolor substances. In particular, it is a useful bleach for paper and clothing. This bleaching effect usually does not last long. Oxygen in the air re-oxidizes the reduced dye, restoring the color.
Sulfuric acid precursor
Sulfur dioxide is also used to prepare sulfuric acid, which is first converted into sulfur trioxide, then into oleum, and finally into sulfuric acid. Sulfur dioxide in this process is produced by the reaction of sulfur-containing minerals with oxygen. The process of converting sulfur dioxide into sulfuric acid is called the contact method.
Refrigerant
SO2 is easily liquefied and has a large heat of vaporization, it is suitable as a refrigerant. Before the development of Freon, sulfur dioxide was used as a refrigerant in household refrigerators.
Reagents and Solvents
Liquid sulfur dioxide is a versatile inert solvent widely used to dissolve strong oxidizing salts. It undergoes auto-ionization to generate SO2+ and SO32-.2SO2→SO2+ +SO32- It is also sometimes used as the source of sulfonyl in organic synthesis. The corresponding arylsulfonyl chloride can be obtained by treating the aryldiazonium salt with sulfur dioxide.
Dechlorination
In urban sewage treatment, sulfur dioxide is used to treat chlorinated sewage before discharge. Sulfur dioxide reacts with chlorine gas, and chlorine gas is reduced to generate Cl-.
