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.

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In the presence of an exogenous two-electron donor, the enzyme is largely protected from hydrogen peroxide because the halogenation cycle is favored.
However, functionalization of porphyrin derivatives had been limited to electrophilic substitution such as halogenation, nitration and formylation, which proceed selectively at the meso-positions in the case of meso-unsubstituted porphyrins such as 15 (Scheme 9).
Halogenation does not reduce Cryptosporidiurn below the microbiological hazard of 99.9%, but it is generally accepted to effectively treat viruses, bacteria, and other protozoa after filtering through a cloth to remove large particles.
The increased effect could be due to the increasing degree of halogenation.
halogenation. When carried out using chlorine as the active element--as
Technologies at the plant include nitration, hydrogenation, halogenation, phosgenation and oxidation.
The list of successful reactions completed in the new liquids rings familiar to any college organic chemistry student: hydrogenation, nitration, halogenation, Diels-Alder, Friedel-Crafts, and on and on.
178 HOFFMANN P,B S CHIM FR,vol 0129,page 0085,1992,cites= 13,PREPARATION AND CATALYTIC ACTIVITIES OF THE MANGANESE AND IRON DERIVATIVES OF BR8TMP AND CL12TMP, 2 ROBUST PORPHYRIN LIGANDS OBTAINED BY HALOGENATION OF TETRAMESITYLPORPHYRIN
Two of these general reactions are oxidation-reduction (redox) and halogenation.
In order to achieve this objective the proposal brings together 3 partners with complementary skills:university of naples (unina): expertise in medicinal chemistry and drug discovery.kelada pharmachem: expertise in green chemistry, chemical batch process development and scale-up.uco: expertise in process engineering of continuous flow processes.we have broken this proposal into the following separate technical work packages:wp1: preparation of new catalysts for efficient desymmetrization wp leader: unina .wp2: development of enantiospecific halogenation including fluorination.
On commercial scale bromocyclopentane is formulated through numerous methods such as free radical halogenation reaction between alkanes & bromine, from alkene & alkynes, nucleophilic substitution of alcohol, and from carboxylic acids.
Various factors and physicochemical properties have been shown to influence partitioning between maternal serum and breast milk including molecular weight, molecular size, steric hindrance, lipophilicity, and halogenation (Needham et al.