page_title: Photochlorination
section_title: Chloromethanes
hierarchical_section_title: Photochlorination / Products / Chloromethanes
caption_attribution_description: Deutsch: Photochlorierung von Methan
context_page_description: Photochlorination is a chemical reaction which is initiated by light, in which either hydrogen is replaced by chlorine in a hydrocarbon compound or chlorine is reacted via an addition reaction to an aromatic or olefinic hydrocarbon. Photochlorination is carried out in addition to thermal and catalytic chlorination on an industrial scale, usually in the liquid phase, sometimes in the presence of inert solvents. The process is exothermic and proceeds as a chain reaction initiated by the homolytic cleavage of molecular chlorine into chlorine radicals by ultraviolet radiation.
  The chlorinated hydrocarbons produced via photochlorination are often only industrial intermediates and react with a large number of basic chemicals to secondary products such as alcohols, mercaptans, amines and carboxylic acids. The chemical industry uses low molecular weight chlorinated compounds, such as tetrachloromethane, as solvents. Higher molecular-weight chloroalkanes serve as insecticides, as flame retardants or as plasticizers in plastics and coatings. Chlorinated hydrocarbons are also used as intermediates in the chemical industry for the production of silicones or detergents.
context_section_description: An example of photochlorination at low temperatures and under ambient pressure is the chlorination of chloromethane to dichloromethane. The liquefied chloromethane (boiling point -24 °C) is mixed with chlorine in the dark and then irradiated with a mercury-vapor lamp. The resulting dichloromethane has a boiling point of 41 °C and is later separated by distillation from methyl chloride.
  The photochlorination of methane has a lower quantum yield than the chlorination of dichloromethane. Due to the high light intensity required, the intermediate products are directly chlorinated, so that mainly tetrachloromethane is formed.
caption: Subsequent products of photochlorination of methane (schematic representation without consideration of stoichiometry).
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