Abstract
Aqueous solution phase photochemistry of the herbicide bromoxynil (3,5- dibromo-4-hydroxybenzonitrile) (1) in the presence of various concentrations of sodium chloride was extensively investigated with ultraviolet radiations near 313 nm. In the presence of 0.5 to 25.0 X 10-3 M NaC1, the quantum yields for the phototransformation of the herbicide bromoxynil (1) amounted to 0.045 ± 0.005 to 0.017 ± 0.007, whereas such data was 0.052 ± 0.004 in the absence of sodium chloride. These quantum yield data for the photolysis of 1 in the absence and presence of sodium chloride followed the Stern-Volmer equation, thereby indicating that NaC1 apparently exerted quenching effects on the photolysis of the compound 1. The rates of photodegradation of the herbicide 1 in water were slower with than without the presence of sodium chloride.
For instance, the photolysis of the 7.8 × 10-6 M aqueous solution of the herbicide 1 in the presence of NaC1 (10.0 X 10-3 M) resulted in the formation of 3-bromo-4-hydroxybenzonitrile (2), 3-bromo-5-chloro-4-hydroxybenzonitrile (3), 3-chloro-4-hydroxybenzonitrile (4), and 4-hydroxybenzonitrile (4A). In the case of this photoreaction of the chemical 1, the percentages of maximum concentrations of the photoproducts 3, 2, 4, and 4A were obtained after 10.5, 20.0, 30.0, and 44.0-min exposures to UV light, respectively, the percentage disappearance of the starting herbicide 1 being ca. 90% for 44-min photolysis. Photoproducts 2, 3, 4, and 4A were identified by interpreting the GC-MS data.
The formation of 4-hydroxybenzonitrile (4A) decreased with the rise in concentration of NaCl. For example, when a mixture of aqueous solutions of 3.0 mL bromoxynil (2.0 X 10-4 M) plus 0.5 mL NaC1 (0.5 M) was exposed to UV light for up to 3 h, the photoproduct 4A could not be observed; however, other products, namely, phenols 2-4 were produced.
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Kochany, J., Choudhry, G.G., Webster, G.R.B. (1991). Environmental Phototransformation of the Herbicide Bromoxynil (3,5-Dibromo-4-Hydroxybenzonitrile) in Aquatic Systems Containing Sodium Chloride. In: Pawlowski, L., Lacy, W.J., Dlugosz, J.J. (eds) Chemistry for the Protection of the Environment. Environmental Science Research, vol 42. Springer, Boston, MA. https://doi.org/10.1007/978-1-4615-3282-8_22
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DOI: https://doi.org/10.1007/978-1-4615-3282-8_22
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