halogenation

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halogenation

[‚hal·ə·jə′nā·shən]
(organic chemistry)
A chemical process or reaction in which a halogen element is introduced into a substance, generally by the use of the element itself.

Halogenation

A chemical reaction or process which results in the formation of a chemical bond between a halogen atom and another atom. Reactions resulting in the formation of halogen-carbon bonds are especially important. The halogenated compounds produced are employed in many ways, for example, as solvents, intermediates for numerous chemicals, plastic and polymer intermediates, insecticides, fumigants, sterilants, refrigerants, additives for gasoline, and materials used in fire extinguishers.

Halogenation reactions can be subdivided in several ways, for example, according to the type of halogen (fluorine, chlorine, bromine, or iodine), type of material to be halogenated (paraffin, olefin, aromatic, hydrogen, and so on), and operating conditions and methods of catalyzing or initiating the reaction.

Halogenation reactions with elemental chlorine, bromine, and iodine are of considerable importance. Because of high exothermocities, fluorinations with elemental fluorine tend to have high levels of side reactions. Consequently, elemental fluorine is generally not suitable for direct fluorination. Two types of reactions are possible with these halogen elements, substitution and addition.

Substitution halogenation is characterized by the substitution of a halogen atom for another atom (often a hydrogen atom) or group of atoms (or functional group) on paraffinic, olefinic, aromatic, and other hydrocarbons. A chlorination reaction of importance that involves substitution is that between methane and chlorine.

Addition halogenation involves a halogen reacting with an unsaturated hydrocarbon. Chlorine, bromine, and iodine react readily with most olefins; the reaction between ethylene and chlorine to form 1,2-dichloroethane is of considerable commercial importance, since it is used in the manufacture of vinyl chloride.

Addition reactions with bromine or iodine are frequently used to measure quantitatively the number of —CH═CH— (or ethylenic-type) bonds in organic compounds. Bromine numbers or iodine values are measures of the degree of unsaturation of the hydrocarbons.

Substitution halogenation on the aromatic ring can be made to occur via ionic reactions. The chlorination reactions with elemental chlorine are similar to those used for addition chlorination of olefins.

References in periodicals archive ?
FIGURE: 05 VALUE FORECAST: GLOBAL MARKET FOR HALOGENATED FLAME RETARDANT CHEMICALS BY INTERMEDIATE APPLICATIONS, 2015 AND 2020 (%)
To examine DNA damage induced by BT, we used an immuno-cytometric method to evaluate halogenated DNA, and we determined 8-oxo-deoxy-guanosine (8-oxo-dG) levels using high-performance liquid chromatography (HPLC) coupled with electrochemical detection (ECD).
Based on comparable calculations from halogenated gas emissions in the atmosphere from present-day salt seas in the south of Russia, the scientists calculated that from the Zechstein Sea alone an annual VHC emissions rate of at least 1.
Halogenated fire retardants are used primarily in the foam of upholstered furniture.
Here's one of the exceptions I mentioned: Non-ionic halogenated compounds can also be used as raw materials in soldering fluxes to help keep activators working as process temperatures increase, but they are used in far smaller quantities than in boards or components, and their inclusion is not an absolute necessity.
In the past decade, routine analyses of animal and food samples, including marine mammals, human breast milk, and commercially available fish, have begun to uncover halogenated organic compounds that could not be easily traced to known industrial or natural sources.
Because halogenated compounds break down extremely slowly, they persist in soil and water and accumulate in animal flesh.
25th International Symposium on Halogenated Environmental Organic Pollutants and POPs (Dioxin 2005), National Water Research Institute, Toronto, ON.
NIST scientists, in collaboration with researchers from the Institute of Energy Problems of Chemical Physics, Russian Academy of Sciences, have developed a simplified method of calculating global warming potentials (GWPs) of halogenated compounds.
For example, in 2006 the European Union banned the use of certain halogenated flame retardants due to environmental and health concerns.
Key statement: A thermoplastic elastomer composition having a continuous phase and a dispersed phase, wherein the continuous phase comprising an epoxy-modified polyamide resin and the dispersed phase comprising a halogenated isoolefin-paraalkylstyrene copolymer rubber, wherein the thermoplastic elastomer composition is obtained by melt-kneading halogenated isoolefm-paraalkylstyrene copolymer rubber, a polyamide resin, and a polyfiinctionai epoxy compound having two or more epoxy groups per molecule in an amount of 0.
It is comprised of at least one surfactant selected from the group consisting of anionic, nonionic, cationic, zwitterionic, amphoteric surfactants, and mixtures thereof; benzyl alcohol; ethanol; at least one hydrotrope; a single antibacterial active selected from the group consisting of halogenated benzyl alcohol derivatives, halogenated hydroxydiphenylethers, quaternary ammonium salts, a peroxide bleach system; and at least one sequestering agent.