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Environmental fate & pathways

Phototransformation in air

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Description of key information

Based on the experimentally determined reaction rate constant a half-life of 7.27 h can be estimated for alpha-methylstyrene. Acetophenone and formaldehyde were observed as main breakdown products which underwent further decomposition. A half-life t1/2=7.2 h was calculated using EPIWIN v3.11, AOPWIN v1.91. In addition, alpha-methylstyrene present in air will be degraded by reaction with ozone (t1/2=2 h, calculated via EPIWIN). Due to the spectral properties of alpha-methylstyrene (absorption of  light in the environmental UV spectrum) direct photolysis is to be expected.

Key value for chemical safety assessment

Half-life in air:
7.27 h

Additional information

The rates of the reactions of OH radicals with styrene, alpha-methylstyrene, and beta-methylstyrene were measured by irradiating mixtures of these aromatic olefins and NO in an environmental chamber at 298K. Based on the experimentally determined reaction rate constant k(OH)=5.3 +/- 0.6 x 10E-11 cm³/molecule x sec (25°C) and assuming a tropospheric OH radical concentration of 5 x 10E5 radicals/cm³ (24 h day) a half-life of 7.27 h can be estimated for alpha-methylstyrene. Based on the results, alpha-methylstyrene present in air is expected to be rapidly photodegraded by reaction with OH radicals. Acetophenone and formaldehyde were observed as main breakdown products which underwent further decomposition. Similar results were obtained using the generally accepted calculation model EPIWIN v3.11, AOPWIN v1.91 (t1/2=7.2 h). The reaction of alpha-methylstyrene with ozone is a further elimination path (t1/2=2 h, calculated via EPIWIN). Due to the spectral properties of alpha-methylstyrene (absorption of light in the environmental UV spectrum) direct photolysis is to be expected.