Mechanism of aqueous decomposition of trichloroethylene oxide

The aqueous decomposition of trichloroethylene (TCE) oxide is shown to invo lve both pH-independent and hydronium ion-dependent regions. C-C bond sciss ion is a major reaction at all pH values. Disappearance of TCE oxide is the rate-determining step fur the formation of CO under the conditions studied . The product distribution of CO and three carboxylic acids (HCO2H, Cl2CHCO 2H, and glyoxylic acid) did not change considerably over the pH range of -1 .5-14, in general, even though the hydrolysis mechanism changes from hydron ium ion-dependent to pH-independent. Mechanisms for the hydronium ion-depen dent and pH-independent hydrolysis of TCE oxide were elucidated on the basi s of the results of (H2O)-O-18 and H incorporation and identification of pr oducts of the reaction of TCE oxide with lysine in both (H2O)-O-16 and (H2O )-O-18. In the pH-independent hydrolysis, a zwitterionic intermediate could be formed and undergo an intramolecular rearrangement (Cl- shift) to gener ate dichloroacetyl chloride, which would subsequently decompose to Cl2CHCO2 H. The zwitterionic intermediate could also hydrolyze at the less stericall y hindered methylene to give a glycol anion, which would dehydrohalogenate to form an oxoacetyl chloride intermediate. The oxoacetyl chloride could hy drolyze to generate either glyoxylic acid, as a final product, or an anioni c intermediate, which could, go through a concerted mechanism to generate C O, HCO2H, and chloride. A mechanism proposed for the hydronium ion-dependen t hydrolysis is very similar to that for the pH-independent hydrolysis exce pt for the first step, which involves hydronium ion attack on TCE oxide to form a TCE-oxide cation intermediate. The lysine amide adducts were charact erized by HPLC and mass spectrometry as those resulting from reaction with the postulated acyl chlorides.