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(3-chloropropyl)diethoxymethylsilane and its hydrolysis product (3-chloropropyl) methylsilanediol contain no chromophores that would absorb visible or UV radiation so direct photolysis is not likely to be significant. Indirect photolysis resulting from gas-phase reaction with photo chemically-produced hydroxyl radicals may occur.

The SRC AOPWIN program(v1.92)has been used to obtain values of the rate constantkOHfor reaction of (3-chloropropyl)diethoxymethylsilaneand (3-chloropropyl)methylsilanediolwith hydroxyl radicals. This prediction method has not been validated to assess applicability to silanes and silanols; therefore, there is uncertainty associated with the calculated values obtained.

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 given in table 4.1.2.

 

Table4.1.1Results of photodegradation in air calculations

Parameter

Result, (3-chloropropyl)diethoxymethylsilane

Result, (3-chloropropyl)methylsilanediol

kOH (cm3 / molecule.sec)

14.6 x 10-12

6.1 x 10-12

kdegair (d-1)

0.63

0.26

DT50 (days)

1.1

2.7