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Environmental fate & pathways

Phototransformation in air

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Description of key information

The rate constant for the reaction of 2-methylpropane-2-thiol with OH radicals is 34.2 to 35.7 E-12 cm3 molecule-1 s-1. Using the equation: Ln2 / (OH concentration * rate constant * 60 * 60 * daylight length), with OH concentration being 1.56 E6 and a daylight length of 12 hours, this gives an atmospheric half-life of 0.288 to 0.301 days.

Key value for chemical safety assessment

Half-life in air:
0.301 d

Additional information

Atkinson (1989) is a review paper that includes and extends previous review articles by the author. Some general information is given about experimental methods and conditions. The paper can be considered reliable and suitable for use as the key study for this endpoint.

A QSAR has been used to support this result. The use of a QSAR to predict the rate constant for the reaction of 2 -methylpropane-2 -thiol with OH radicals is an appropriate technique and is suitable for use for this endpoint. The Aopwin model divides the substance by structure into 'fragments' of atoms or functional groups and uses the total of the coefficients assigned to each of these ‘fragments’ within the substance to estimate the rate constant. Though there is no applicability domain for this model, the substance falls within the molecular weight and other substances with an -SH functional group are included in the training set. The estimated value is in good agreement with the experimental value for 2 -methylpropane-2 -thiol used in the database.

The experimental and estimated results are in agreement with other literature values: Barnes (1987), Barnes (1986) and Atkinson (1987).