Trichloroacetaldehyde 2,2,2-trichloroethanal

Chlorinated by-products of ethylene oxychlorination typically include 1,1,2-trichloroethane chloral [75-87-6] (trichloroacetaldehyde) trichloroethylene [7901-6]-, 1,1-dichloroethane cis- and /n j -l,2-dichloroethylenes [156-59-2 and 156-60-5]-, 1,1-dichloroethylene [75-35-4] (vinyhdene chloride) 2-chloroethanol [107-07-3]-, ethyl chloride vinyl chloride mono-, di-, tri-, and tetrachloromethanes (methyl chloride [74-87-3], methylene chloride [75-09-2], chloroform, and carbon tetrachloride [56-23-5])-, and higher boiling compounds. The production of these compounds should be minimized to lower raw material costs, lessen the task of EDC purification, prevent fouling in the pyrolysis reactor, and minimize by-product handling and disposal. Of particular concern is chloral, because it polymerizes in the presence of strong acids. Chloral must be removed to prevent the formation of soflds which can foul and clog operating lines and controls (78). 

An overview of the reactions involving trihalomethanes (haloforms) CHXYZ, where X, Y, and Z are halogen atoms, has been given in the context of ozone depletion (Hayman and Derwent 1997). Interest in the formation of trichloroacetaldehyde formed from trichloroethane and tetrachloroethene is heightened by the phytotoxicity of trichloroacetic acid (Frank et al. 1994), and by its occurrence in rainwater that seems to be a major source of this contaminant (Muller et al. 1996). The situation in Japan seems, however, to underscore the possible significance of other sources including chlorinated wastewater (Hashimoto et al. 1998). Whereas there is no doubt about the occurrence of trichloroacetic acid in rainwater (Stidson et al. 2004), its major source is unresolved since questions remain on the rate of hydrolysis of trichloroacetaldehyde (Jordan et al. 1999). 

Hydrates cannot be isolated from the ketones and aldehydes seen most often in this book, but in a few special cases a hydrate is isolated. If the carbon attached to the carbonyl carbon (the a-carbon) has strong electron-withdrawing groups on it—and, particularly, if no hydrogens are on the a-carbon adjacent to the carbon bearing the two OH units—the hydrate may be isolated. Chloral (40) is a common name for trichloroethanal (trichloroacetaldehyde is also used as a common name) and it reacts with water to form a stable hydrate, 41. 

Finally, in this vein, and as noted earlier for electrophilic substitution in alkyl-substituted arenes, a variety of substitutions can be effected. Among these is the Friedel-Crafts-type acylation of chlorobenzene (CeHsCl) by 2,2,2-trichloroethanal (trichloroacetaldehyde, chloral [CCI3CHO]), which, as shown in Scheme 7.15, results in the formation of l,l,l-trichloro-2-[di(p-chlorophenyl)]ethane (dichlorodiphenyl-trichloroethane [DDT]). 

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