The Aqueous Photolysis of TFM and Related Trifluoromethylphenols. An Alternate Source of Trifluoroacetic Acid in the Environment

The lampricide 3-trifluoromethyl-4-nitrophenol (TFM) is added annually to the Great Lakes (approximately 50 000 kg/y), with treatment concentrations varying from 1 to 14 mg/L at source. TFM was shown to undergo photohydrolytic degradation, at 365 nm and under actinic radiation, to produce trifluoroacetic acid (TFA). A mechanistic study for the production of TFA from TFM was conducted, and the structural parameters associated with the production of TFA from trifluoromethylated phenols were investigated. It was found that the yield of TFA is clearly dependent on the nature of the trifluoromethylated phenol. The nature of the substituents, the substitution pattern, and the pH strongly effected the photolytic half-life of the parent compound and the yield of TFA. The half-life of TFM at 365 nm was found to be 22 h (pH 9) and yielded 5.1% TFA, and 91.7 h at pH 7, yielding 17.8% TFA. Converting the nitro substituent of TFM to an amino group caused a decrease in the half-life to 2.3 min and yielded 11% TFA. The mechanism for the production of TFA from TFM was deduced from the pH dependence and the effect of altering substituents on the trifluoromethylphenol. Ultimately, the formation of trifluoromethylquinone led to the quantitative production of TFA.