REACTION OF THE OH RADICAL WITH TETRACHLOROETHENE AND TRICHLOROACETALDEHYDE (HYDRATE) IN OXYGEN-FREE AQUEOUS-SOLUTION

Hydroxyl radicals are generated radiolytically in N2O-saturated aqueous solutions and are reacted with either tetrachloroethene or trichloroacetaldehyde hydrate. The primary products after irradiation are tetrachlorosuccinic acid (G = 2.3 x 10(-7) mol J(-1) and 2.7 x 10(-7) mol J(-1), respectively) and chloride ions (G = 11.6 x 10(-7) mol J(-1) and 7.3 x 10(-7) mol J(-1), respectively). The former decomposes into trichloroacrylic acid and carbon dioxide (E(a) = 115 kJ mol(-1)). From tetrachloroethene -some dichloroacetic acid is also formed (G = 0.2 x 10(-7) mol J(-1)). Trichloroacetic acid is not among the products. Kinetic studies were carried out by pulse radiolysis. In the case of trichloroacetaldehyde hydrate there is a jump in conductivity increase of G(H+) approximate to 2 x G((OH)-O-.) within less than or equal to 5 mu s and no further increase in conductivity at later times. It is concluded that the OH-radicals abstract the carborn-bound H-atom and the resulting CCl3C(OH)(2)(.) radicals rapidly eliminate HCl forming (CCl2CO2H)-C-. radicals which dissociate and dimerize yielding tetrachlorosuccinic acid. In the case of the reaction of the OH-radical with tetrachloroethene the conductivity build-up is biphasic. In the first step one equivalent H+ is formed when the primary (CCl2CCl2OH)-C-. radical eliminates HCl yielding the (CCl2C)-C-.(O)Cl radical (k > 7 x 10(5) s(-1)). Upon dimerization (2 k = 6.9 x 10(8) dm(3) mol(-1) s(-1)) Cl(O)CCCl2CCl2C(O)Cl is formed-which hydrolyses (k = 5 s(-1)). Only one conductivity equivalent is liberated, and it is concluded that the ensuing monoanion rapidly eliminates a chloride ion (no conductivity change) yielding tetrachlorosuccinic anhydride. It subsequently hydrolyses at a later stage, not resolved by pulse radiolysis, to tetrachlorosuccinic;acid.