1,1,1-trichloroethane photochemical chlorination

Acetylene and hydrogen chloride historically were used to make chloroprene [126-99-8]. The olefin reaction is used to make ethyl chloride from ethylene and to make 1,1-dichloroethane from vinyl chloride. 1,1-Dichloroethane is an intermediate to produce 1,1,1-trichloroethane by thermal (26) or photochemical chlorination (27) routes. 

Trichloroethane is also a coproduct in the thermal and photochemical chlorination of 1,1-dichloroethane to produce 1,1,1-trichloroethane. Vapor chlorination favors the 1,1,1-isomer, whereas reaction in the Hquid phase may give much higher ratios of 1,1,2-trichloroethane. V-type 2eohtes have been used in vapor-phase chlorination of 1,1-dichloroethane to produce 1,1,2-trichloroethane in high selectivity (100). 

The most common method for industrial preparation of 1,1,1-trichloroethane is the reaction of hydrochloric acid with vinyl chloride (obtained from 1,2-dichloroethane) to obtain 1,1-dichloroethane, followed by either thermal or photochemical chlorination. Other methods include the catalyzed addition of hydrogen chloride to 1.1-dichloroethylene, and the direct chlorination of ethane itself, followed by separation from the other products produced (Archer 1979). Commercial grades of... 

Detailed studies of the chlorine-atom-sensitized oxidation of chloromethane, dichloromethane, 1,1,2-trichloroethane, CH2CC12, and C2C14148 have been reported. Reports on the photolysis of Freons of interest to upper-atmosphere chemistry are discussed in the last section of this Report, and laser enhancement of some halogen-containing molecular reactions is discussed in Section 11. A paper concerned with the mechanism of photodissociation of alkyl and aryl halides was discussed earlier.38 The photochemical chlorination of 1,2-dichloroethane149 and fluorination of carbonyl fluoride,150 reactions of 2 radicals,151 and the photochemical decomposition of FaO at elevated temperatures152 have been reported. 

Trichloroethane is produced by photochemical chlorination of 1,1-dichloroe-thane, which is obtaind by the addition of HCl to vinylchloride in presence of a catalyst... 

Methane, chlorine, and recycled chloromethanes are fed to a tubular reactor at a reactor temperature of 490—530°C to yield all four chlorinated methane derivatives (14). Similarly, chlorination of ethane produces ethyl chloride and higher chlorinated ethanes. The process is employed commercially to produce l,l,l-trichloroethane. l,l,l-Trichloroethane is also produced via chlorination of 1,1-dichloroethane with l,l,2-trichloroethane as a coproduct (15). Hexachlorocyclopentadiene is formed by a complex series of chlorination, cyclization, and dechlorination reactions. First, substitutive chlorination of pentanes is carried out by either photochemical or thermal methods to give a product with 6—7 atoms of chlorine per mole of pentane. The polychloropentane product mixed with excess chlorine is then passed through a porous bed of Fuller s earth or silica at 350—500°C to give hexachlorocyclopentadiene. Cyclopentadiene is another possible feedstock for the production of hexachlorocyclopentadiene. 

Addition Chlorination. Chlorination of olefins such as ethylene, by the addition of chlorine, is a commercially important process and can be carried out either as a catalytic vapor- or Hquid-phase process (16). The reaction is influenced by light, the walls of the reactor vessel, and inhibitors such as oxygen, and proceeds by a radical-chain mechanism. Ionic addition mechanisms can be maximized and accelerated by the use of a Lewis acid such as ferric chloride, aluminum chloride, antimony pentachloride, or cupric chloride. A typical commercial process for the preparation of 1,2-dichloroethane is the chlorination of ethylene at 40—50°C in the presence of ferric chloride (17). The introduction of 5% air to the chlorine feed prevents unwanted substitution chlorination of the 1,2-dichloroethane to generate by-product l,l,2-trichloroethane. The addition of chlorine to tetrachloroethylene using photochemical conditions has been investigated (18). This chlorination, which is strongly inhibited by oxygen, probably proceeds by a radical-chain mechanism as shown in equations 9—13. 

Addition. Chlorine adds to vinyl chloride to form 1,1,2-trichloroethane [79-00-5] (44—46). Chlorination can proceed by either an ionic or a radical path. In the liquid phase and in the dark, 1,1,2-trichloroethane forms by an ionic path when a transition-metal catalyst such as ferric chloride [7705-08-0], FeCl3, is used. The same product forms in radical reactions up to 250°C. Photochemically initiated chlorination also produces... 

Under laboratory conditions thought to mimic atmospheric smog conditions, direct photochemical irradiation of 1,1,1-trichloroethane in the presence of elemental chlorine was performed. 1,1,1-Trichloroethane was the least reactive and thus the most stable of all chloroethanes under these conditions (Spence and Hanst 1978). 

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