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Key value for chemical safety assessment

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The SRC AOPWIN program (v1.92) has been used to obtain values of the rate constant kOH for the reaction of dimethoxymethylsilane and methylsilanetriol with hydroxyl radicals. This prediction method has not been validated to assess applicability to silanes and silanols; therefore, the results should be treated with caution.

The overall half-life in air under default conditions of hydroxyl radical concentration was calculated using the following expressions:

kdegair(d-1) = kOH(cm3/molecule.sec) x OH Concair(molecules/cm3) x 24 x 3600

DT50(d) = ln 2/ kdegair(d-1)

Where:

kdegair= total rate constant for degradation in air

kOH= rate constant for reaction with hydroxyl radicals

OH Concair= concentration of hydroxyl radicals in air =5 x 105OH molecules/ cm3

DT50= half-life

The results are presented in Table 4.1.2.

Table 4.1.2: Calculated photodegradation in air.

Parameter

Result: Dimethoxymethylsilane

Result: Methylsilanetriol

kOH(cm3/ molecule.sec)

1.808 x 10-12

10.5 x10-12

kdegair (d-1)

0.07

0.5

DT50(days)

8.8

1.5