REACTION OF 1,1,1-TRICHLOROETHANE WITH ZERO-VALENT METALS AND BIMETALLIC REDUCTANTS

Information concerning the pathways and products of reaction of 1,1,1 -trichloroethane (1,1,1-TCA) with zero-valent metals may be critical t o the success of in situ treatment techniques. Many researchers assume that alkyl polyhalides undergo reduction via stepwise hydrogenolysis (replacement of halogen by hydrogen). Accordingly, 1,1,1-TCA should re act to 1,l-dichloroethane (1,1-DCA), to chloroethane, and finally to e thane. Experiments conducted in laboratory-scale batch reactors indica te, however, that with zinc, iron, and two bimetallic reductants (nick el-plated iron and copper-plated iron) this simplistic stepwise scheme cannot explain observed results. 1,1,1-TCA was found to react rapidly with zinc to form ethane and 1,1-DCA. Independent experiments confirm ed that 1,1-DCA reacts too slowly to represent an intermediate in the formation of ethane. in reactions with iron, nickel/iron, and copper/i ron, cis-2-butene, ethylene, and 2-butyne were also observed as minor products. Product ratios were dependent on the identity of the metal o r bimetallic reductant, with zinc resulting in the lowest yield of chl orinated product. For reactions with iron and bimetallic reductants, a scheme involving successive one-electron reduction steps to form radi cals and carbenoids can be invoked to explain the absence of observabl e intermediates, as well as the formation of products originating from radical or possibly from carbenoid coupling.