The six chemical elements found in group 17 (VIIA) of the periodic table are called halogens. They exhibit similar chemical behaviors, such as forming very similar sodium (Na) salts. Hence their name, which comes from the Greek words hals- (“salts”) and genes (“origin”).
Halogens are highly reactive, so they are never found in their monoatomic form, but as part of other compounds. At most they can be found forming diatomic molecules of the same element. For example: F2, Cl2, Br2 and I2.
Halogens are used on numerous occasions, such as in the form of edible salts or tinctures for medical use. They are used in the manufacture of lamps, bleaches and detergents. They are used in the treatment of drinking water and swimming pool water (especially chlorine).
Iodine is fixed in the tissues of shellfish and fish. Astatine, being a short-lived radioactive material, is rarely found. Tenesium exists only in laboratories, as it is a synthetic element.
Halogenation of benzene
Halogenation is the chemical process by which one or more atoms of elements of the halogen group (group 17 of the periodic table) are added or substituted to an organic molecule. One of the simplest halogenations is the halogenation of alkanes. In these reactions the hydrogen atoms of the alkanes are always fully or partially replaced by atoms of the halogen group. The reaction that takes place is as follows:
A wide variety of chemical products are possible. The composition of the product mixture will be given by the concentration of the reactants and other conditions of the reaction medium, e.g. temperature.
In a Markovnikov addition reaction, a halogen such as bromine is reacted with an alkene which causes the π-bond of the double bond to be broken to give the formation of a single bonded haloalkane. This makes the hydrocarbon more reactive, and bromine, as a result, is a good leaving group in various chemical reactions such as aliphatic nucleophilic substitution reactions and elimination reactions.
These are organic chemicals containing one or more atoms of a halogen element (usually chlorine, although there are compounds formed with bromine and iodine). They can be simple and volatile substances such as trichloromethane (chloroform), or complex organic molecules such as dioxins and furans, which can have a wide variety of physical properties.
The main source of contamination of these compounds originates in the paper industry, where chlorine is used to bleach cellulose fibers. Other minor sources of emissions are generated during the disinfection with chlorine of drinking water in swimming pools and process water in laundries.
Excessive exposure to these chemical substances can generate adverse effects on human health, although the symptoms and alterations produced will depend on the type of substance and the duration of exposure.
Most of these compounds are toxic to aquatic organisms at low concentrations, as they are very persistent in the environment and tend to bioaccumulate, even being transmitted to humans through the food chain.
Alkane halogenation pdf
Organic Synthesis is a field of work that allows access to an infinite number of molecules of great relevance, such as the drugs we use to fight diseases. This area of work could be likened to a workshop in which mechanical components are manufactured and, as in any workshop, it is essential to have the most complete toolbox possible to carry out the work efficiently. In the case of Organic Synthesis, this toolbox would be the Synthetic Methodology that provides the necessary synthetic methods to prepare complex molecules.
One such synthetic methodology is the halogenation of double bonds to generate alkyl halides. This method is doubly important since, on the one hand, it is a very recurrent transformation in synthesis, and on the other hand, alkyl halides are compounds of great relevance since they are reaction intermediates widely used in the synthesis of complex products. There are several methods to carry out this halogenation reaction and in all of them the key lies in being able to control the position in which the halogen atom is incorporated.