1,1,2,2-tetrachloroethane, dehydrochlorination

Pyrolysis Thermal decomposition of 1,1,1,2-tetrachloroethane produces tetrachloroethylene (by disproportionation), hydrogen chloride, and trichloroethylene via dehydrochlorination (111). The yield of the latter is increased in the presence of ferric chloride (112). Other catalytic materials include FeCl —KCl mixture (113), AlCl (6), the complex of AlCl with nitrobenzene (114), activated alumina (3), Ca(OH)2 (115,116), and NaCl (94). 

Dehydrochlorination and Chlorination. The simultaneous chlorination and dehydrochlorination of 1,1,2,2-tetrachloroethane proceeds via formation of labile intermediate, CI2CCHCI2 (123). Chlorination of tetrachloroethane to hexachloroethane is accelerated by 315—354 nm light (124). 

Many processes have been used to produce tetrachloroethylene. One of the first was chlorination of acetylene (C2H2) to form tetrachloroethane, followed by dehydrochlorination to trichloroethylene. If tetrachloroethylene was desired, the trichloroethylene was further chlorinated to pentachloroethane and dehydrochlorinated. This process is no longer used in the United States Hooker Chemical closed down the last plant in 1978. 

In Japan, Toagosei is reported to produce trichloroethylene and tetrachloroethylene by chlorination of ethylene followed by dehydrochlorination. In this process the intermediate tetrachloroethane is either dehydrochlorinated to trichloroethylene or further chlorinated to pentachloroethane [76-01-7] followed by dehydrochlorination to tetrachloroethylene. Partially chlorinated by-products are recycled and by-product HCl is available for other processes. 

More general cases are encountered in the metabolism of a variety of ha-log enated hydrocarbon solvents and insecticides [58]. Examples include the dehydrochlorination of 1,1,2,2-tetrachloroethane to trichloroethylene in the mouse, and of DDT (l,l,l-trichloro-2,2-bis(4-chlorophenyl)ethane) to DDE (l,l-dichloro-2,2-bis(4-chlorophenyl)ethene) [58][77]. Glutathione transferases may be involved in some of these reactions. 

Dicofol (4) is prepared by the chlorination of chlorfenethol (2), or by the partial hydrolysis of l,l-bis(4H hlorophenyl)-l,2,2,2-tetrachloroethane (5), obtained from DDT by dehydrochlorination and subsequent chlorination (Reuter and Ascher, 1956 Wilson et al., 1955 Wilson and Wolffe, 1955). 

Trichloroethylene. Tetrachloroethane from the previous operations is fed with 90 per cent of the required lime slurry to the lower section of a conversion tower, the remainder of the lime slurry being delivered to the head of the middle section. Live steam is blown into the liquid at the base of the tower to maintain a temperature of 103 C. Dehydrochlorination takes place, and the trichloroethylene vapor rising in the tower is scrubbed... 

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