Photochemistry of halogenated benzene derivatives. Part IX.environmental aquatic phototransformation of bromoxynil (3,5‐dibromo‐4‐hydroxybenzonitrile)

摘要

AbstractPhotochemistry of the herbicide 3,5‐dibromo‐4‐hydroxybenzonitrile (bromoxynil) (I) was investigated by irradiating at approximately 313 nm. Aqueous phase photoreactions of 0.078–7.800 × 10−5m solutions of I were carried out at different pH values. Quantum yields for the loss of I in buffered solutions were 0.008 (±0.0004), 0.048 (±0.0024), and 0.044 (±0.0022) at pH 2.6, 7.0, and 11.0, respectively. In neutral and basic conditions, I absorbed more strongly at wavelengths>290 nm, an environmentally significant region. Phototransformation of I was monitored by HPLC and UV‐VIS spectrometry. All photoreactions of I gave rise to the generation of two products, 3‐bromo‐4‐hydroxybenzonitrile and 4‐hydroxybenzonitrile. The former photoproduct was tentatively identified from its mass spectral data. The photoproducts can be accounted for with a proposed mechanism