Sulfur dioxide

Sulfur dioxide is the most common and simplest sulfur oxide, with the chemical formula SO2. It is a colorless, transparent gas with a pungent odor. It is soluble in water, ethanol and ether. Sulfur dioxide is one of the main pollutants in the atmosphere. The gas is ejected during volcanic eruptions and is also produced in many industrial processes. Since coal and oil usually contain sulfur, sulfur dioxide is produced when they are burned. When sulfur dioxide is dissolved in water, sulfurous acid is formed. If sulfurous acid is further oxidized in the presence of PM2.5, sulfuric acid (one of the main components of acid rain) is quickly and efficiently generated. This is one of the reasons for concerns about the environmental effects of using these fuels as energy sources.

Liquid sulfur dioxide has a stable specific price and is inactive. Gaseous sulfur dioxide does not decompose when heated to 2000℃. It does not burn and does not form an explosive mixture with air.

Chemical properties

At room temperature, moist sulfur dioxide reacts with sulfides to precipitate sulfur. Under high temperature and the presence of a catalyst, it can be reduced to hydrogen sulfide by hydrogen and to sulfur by carbon monoxide. Strong oxidants can convert sulfur dioxide into sulfur trichloride. Only in the presence of a catalyst can oxygen oxidize sulfur dioxide into sulfur trioxide. It is self-igniting and non-combustible. Liquid sulfur dioxide can dissolve amines, ethers, and alcohols. Organic compounds such as phenol, organic acids, and aromatic hydrocarbons cannot be dissolved in most saturated hydrocarbons. It has a certain water solubility and reacts with water and water vapor to generate toxic and corrosive vapors.

The chemical properties of sulfur dioxide are extremely complex. It can act as a non-protonic solvent, Lewis acid, reducing agent, oxidizing agent, redox reagent, etc. at different temperatures. Liquid sulfur dioxide can also react with acetylene compounds in the presence of a free radical initiator to obtain polysulfone. Liquid sulfur dioxide can react with chlorine and alkanes under light for chlorosulfonation, and generate sulfonic acid in the presence of oxygen. Liquid sulfur dioxide exhibits reducing effects at low temperatures, but exhibits oxidizing effects above 300°C.

Sulfur dioxide can make the fuchsin solution fade, and the color will be restored after heating, because the bleaching principle of sulfur dioxide is that sulfur dioxide reacts with the bleached material to generate colorless unstable compounds, which destroys the quinone formula that plays a coloring role in fuchsin. When heated, the compound decomposes and restores the original color, so sulfur dioxide bleaching is also called temporary bleaching. It can fade the acidic potassium permanganate solution.

Sulfur dioxide has bleaching properties. It is often used in industry to bleach pulp, wool, silk, straw hats, etc. The bleaching effect of sulfur dioxide is due to its (sulfurous acid) ability to generate unstable colorless substances with certain colored substances. This colorless substance is easy to decompose and restore the original color of the colored substance, so the straw hat bleached by sulfur dioxide will turn yellow again after a long time. The bleaching effect of sulfur dioxide and certain sulfur-containing compounds is also illegally used by some illegal manufacturers to process food to whiten the food, etc. Eating such food will cause serious damage to the liver, kidneys, etc. of the human body and have carcinogenic effects.

In addition, sulfur dioxide can inhibit the growth of mold and bacteria and can be used as a preservative for food and dried fruits. However, it must be used strictly in accordance with relevant national scopes and standards.