Галогенирование: Химические реакции и применение.

Chemical reaction which adds one or more halogen elements to a compound

the addition of chlorine, hypochlorite, etc. to drinking water

In chemistry, halogenation is a chemical reaction which introduces of one or more halogens into a chemical compound. Halide containing compounds are pervasive, making this type of transformation important, e. g. in the production of polymers, drugs. This kind of conversion is in fact so common that a comprehensive overview is challenging. This article mainly deals with halogenation using elemental halogens (|F2, Cl2, Br2, I2). Halides are also commonly introduced using salts of the halides and halogen acids. Many specialized reagents exist for and introducing halogens into diverse substrates, e. g. thionyl chloride.

Several pathways exist for the halogenation of organic compounds, including free radical halogenation, ketone halogenation, electrophilic halogenation, and halogen addition reaction. The nature of the substrate determines the pathway. The facility of halogenation is influenced by the halogen. Fluorine and chlorine are more electrophilic and are more aggressive halogenating agents. Bromine is a weaker halogenating agent than both fluorine and chlorine, while iodine is the least reactive of them all. The facility of dehydrohalogenation follows the reverse trend: iodine is most easily removed from organic compounds, and organofluorine compounds are highly stable.

Because of its extreme reactivity, fluorine (|F2) represents a special category with respect to halogenation. Most organic compounds, saturated or otherwise, burn upon contact with |F2, ultimately yielding carbon tetrafluoride. By contrast, the heavier halogens are far less reactive toward saturated hydrocarbons. Highly specialised conditions and apparatus are required for fluorinations with elemental fluorine. Commonly, fluorination reagents are employed instead of |F2. Such reagents include cobalt trifluoride, chlorine trifluoride, and iodine pentafluoride. The method electrochemical fluorination is used commercially for the production of perfluorinated compounds. It generates small amounts of elemental fluorine in situ from hydrogen fluoride. The method avoids the hazards of handling fluorine gas. Many commercially important organic compounds are fluorinated using this technology.

All elements aside from argon, neon, and helium form fluorides by direct reaction with fluorine. Chlorine is slightly more selective, but still reacts with most metals and heavier nonmetals. Following the usual trend, bromine is less reactive and iodine least of all. Of the many reactions possible, illustrative is the formation of gold(III) chloride by the chlorination of gold. The chlorination of metals is usually not very important industrially since the chlorides are more easily made from the oxides and hydrogen chloride. Where chlorination of inorganic compounds is practiced on a relatively large scale is for the production of phosphorus trichloride and disulfur dichloride.