A substance that promotes oxidation is called a pro-oxidant, and a substance that prevents oxidation is called an antioxidant or an antioxidant. The most easily encountered co-oxidants in most fats or plastics are trace amounts of metal ions, such as copper, manganese, iron, chromium, nickel and vanadium. Antioxidants, which act as reducing agents, can also play the role of pro-oxidants. For example, vitamin C plays an antioxidant role by reducing oxidizing hydrogen peroxide. However, vitamin C can also reduce high-valent transition metal ions through the Fenton reaction, and then the reduced metal ions pass through the reaction. Generate free radicals.
Figure 1. Structure of vitamin C.
In a redox reaction, a substance that acquires electrons is called an oxidant, and a substance that loses electrons is called a reducing agent. In a narrow sense, an oxidant can refer to a substance that can obtain oxygen from another substance, and so on. A fluorinating agent can be a substance that can obtain fluorine from a substance, as well as a chlorinating agent and a brominating agent. Oxidizing agents are commonly used for substances containing easily available electronic elements, that is, substances with strong oxidizing properties. In a word, the oxidant has oxidizing property, the electron valence obtained is reduced, and a reduction reaction occurs to obtain a reduced product. In solution, according to the theory of electric double layer, the size of oxidizing power is reflected by the standard hydrogen electrode potential of oxidizing agent: the higher the potential, the stronger the oxidizing power; the lower the potential, the weaker the oxidizing power, correspondingly, its reduced state The stronger the reducibility. Strong oxidants are oxidizing substances with high potential.
The oxidants are divided into inorganic oxidants and organic oxidants according to their chemical composition. It can also be divided into the following 3 categories according to the media required for the oxidation reaction:
(1) Acidic medium oxidant (example: hydrogen peroxide, peroxyacetic acid, sodium dichromate, chromic acid, nitric acid, potassium permanganate, ammonium persulfate).
(2) An alkaline medium oxidant (example: sodium hypochlorite, sodium percarbonate, sodium perborate, potassium perborate).
(3) Neutral oxidant (example: bromine, iodine).
(1) In the chemical industry, it is widely used in the production of a variety of raw materials and finished products. Pro-oxidant is commonly used in metallurgy to remove impurities and purify the smelted metal. For example, the oxidant used in the steelmaking process is iron ore, iron phosphorus, air or industrial pure oxygen. In chemical batteries, oxidants are commonly used to remove the oxygen released from the positive electrode, which is called "removing agent", such as manganese dioxide used in dry batteries.
(2) The pro-oxidant decomposes when exposed to heat, which can easily cause combustion and explosion, so it must not be heated.
(3) Many pro-oxidant are explosive, such as chlorates, nitrates, and especially organic peroxides. After friction, impact, vibration, etc., they can easily cause explosions, so they must be handled lightly.
(4) It will react strongly with organic matter, flammable materials, combustible materials, etc., and even cause combustion and explosion. Therefore, packaging materials for oxidants, warehouses, and transportation vehicles must be thoroughly cleaned to prevent contamination with impurities and danger.
(5) Most pro-oxidant react violently with acid and even explode, such as potassium chlorate, benzoyl peroxide, etc., and explode when they encounter sulfuric acid. Therefore, these oxidants must not be in contact with acids or alkaline substances; in case of fire, they cannot be extinguished with acid-base fire extinguishers.