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Environmental fate & pathways

Phototransformation in air

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Description of key information

Calculation with AOPWIN v1.92 (EPIWIN software by US-EPA): 
Cis-isomer: overall gas-phase reaction constant: 5.27E-13 cm³/molecules-sec, with an half-life of 2.44 days by assuming a 12 h light day with an OH concentration of 1.5E6 OH/cm³ and 25 °C.
Trans-isomer: overall gas-phase reaction constant: 59.5352E-12 cm³/molecules-sec, with an half-life of 2.16 days by assuming a 12 h day with an OH concentration of 1.5E6 OH/cm³ and 25 °C.

Key value for chemical safety assessment

Additional information

The phototransformation in air of the test substance was determined by the computer program AOPWIN v1.92 (EPIWIN software) by US-EPA (Chemservice S.A., 2012). This tool estimates the gas-phase reaction rate for the reaction between the most prevalent atmospheric oxidant (hydroxyl radicals) and a substance. For olefins and acetylenes the gas-phase ozone radical reaction rates are estimated as well. Additional information is given by the program if nitrate radical reaction will be important. The assumed average hydroxyl radical and ozone concentration are automatically used to calculate the atmospheric half-life for the chemical of interest. For 4-phenylbutenone the results differ to a certain extend in some reaction classes depending which isomer is considered (cis- or trans-isomer). The reaction with hydroxyl radicals is splitted into three classes: “Hydrogen Abstraction”, which gives an OH rate constant of 1.01E-11 cm³/molecule-sec, “Addition to Aromatic Rings”, with an OH rate constant of 1.83E-12 cm³/molecule-sec and “Addition to Olefinic Bonds” – resulting in different overall rate constants, depending which isomer is taken into account: for the cis-isomer the OH rate constant is defined as 5.08E-13 cm³/molecule-sec, whereas the trans-isomer gives a value of 5.76E-13 cm³/molecule-sec. The OVERALL OH rate constant for the cis-isomer is predicted as 5.27E-13 cm³/molecule-sec and 5.95E-13 cm³/molecule-sec for the trans-isomer. The half-lives are predicted as 2.44 hours for the cis-isomer and 2.16 hours for the trans-isomer, assuming a 12 hour light day and an OH rate of 1.5E6/cm³. Furthermore, 4-phenylbutenone will be able to undergo ozone reactions. The cis-isomer possesses an overall ozone rate constant of 2.83E-17 cm³/molecules-sec and a half-life at 7.0E11 mol/cm³ of 9.70 hours, whereby the prediction of the trans-isomer results in an overall ozone rate constant of 5.67E-17 cm³/molecules-sec and a half-life of 4.85 hours. All calculations were performed supposing a surrounding temperature of 25 °C.