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A radical abstracts a hydrogen atom from methane, leaving a primary methyl radical. The methyl radical then abstracts Cl • from Cl 2 to give the desired product and another chlorine radical. Methane chlorination: propagation The radical will then participate in another propagation reaction: the radical chain. Other products such as CH 2 Cl 2 ...
A good example of a substitution reaction is halogenation. When chlorine gas (Cl 2) is irradiated, some of the molecules are split into two chlorine radicals (Cl•), whose free electrons are strongly nucleophilic. One of them breaks a C–H covalent bond in CH 4 and grabs the hydrogen atom to form the electrically neutral HCl.
Alkanes and aryl alkanes may be chlorinated under free radical conditions, with UV light. However, the extent of chlorination is difficult to control. Aryl chlorides may be prepared by the Friedel-Crafts halogenation, using chlorine and a Lewis acid catalyst. [2]
A free-radical reaction is any chemical reaction involving free radicals. This reaction type is abundant in organic reactions . Two pioneering studies into free radical reactions have been the discovery of the triphenylmethyl radical by Moses Gomberg (1900) and the lead-mirror experiment [ 1 ] described by Friedrich Paneth in 1927.
Halogenation of saturated hydrocarbons is a substitution reaction. The reaction typically involves free radical pathways. The regiochemistry of the halogenation of alkanes is largely determined by the relative weakness of the C–H bonds. This trend is reflected by the faster reaction at tertiary and secondary positions.
In organic chemistry, a radical-substitution reaction is a substitution reaction involving free radicals as a reactive intermediate. [1] The reaction always involves at least two steps, and possibly a third. In the first step called initiation (2,3), a free radical is created by homolysis.
The selectivity of photochlorination (with regard to substitution of primary, secondary or tertiary hydrogens) can be controlled by the interaction of the chlorine radical with the solvent, such as benzene, tert-butylbenzene or carbon disulfide. [12] Selectivity increases in aromatic solvents. [13]
Free radical chlorination of methane (under ultraviolet light): CH 4 + Cl 2 → CH 3 Cl + HCl. This method is useful for the production of CH 4−n Cl n (n = 1, 2, 3, or 4). The main problems with this method are that it cogenerates HCl and it produces mixtures of different products.