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EC number: 221-906-4
CAS number: 3277-26-7
Phototransformation in air:
Rate constant for reaction with OH radicals: Parent substance 6.0 x
10-13 cm3/molecule.sec (half-life 27 days), AOPWIN prediction.
Intermediate hydrolysis product: 4.0 x 10-12 cm3/molecule.sec
(half-life 4 days), AOPWIN prediction.
Final hydrolysis product: 8.1 x 10-13 (half-life 20 days) (Tuazon, 2000)
(H2 -L2) and its intermediate and final silanol hydrolysis products,
dimethylsilanol and dimethylsilanediol respectively, contain no
chromophores that would absorb visible or UV radiation. Direct
photolysis is therefore not likely to be significant, however indirect
photolysis resulting from gas-phase reaction with
photochemically-produced hydroxyl radicals may occur.
AOPWIN program (v1.92, EPA 2010) has been used to obtain values of the
rate constant kOHfor reaction of the parent substance
and intermediate and final hydrolysis products with hydroxyl radicals.
This prediction method has not been validated to assess applicability to
organosilicon substances; therefore, there is uncertainty associated
with the calculated values obtained.
overall half-life in air under default conditions of hydroxyl radical
concentration was calculated using the following expressions:
= kOH(cm3/molecule.sec) x OH Concair(molecules/cm3)
x 24 x 3600
= ln 2/ kdegair(d-1)
rate constant for degradation in air
rate constant for reaction with hydroxyl radicals
concentration of hydroxyl radicals in air = 5 x 105OH
concentration of hydroxyl radicals in air of 5 x 105OH
molecules/ cm3, and the 24 hour photoperiod, are the values
specified in ECHA
Guidance on Information requirements and chemical safety assessment,
Part R.16 Environmental exposure estimation (ECHA, 2016).
results are given in the table below:
Results of photodegradation in air calculations
kOH (cm3/ molecule.sec)
0.6 x 10-12
4.0 x 10-12
7.2 x 10-12
Measured data for reaction with hydroxyl radicals in air are
available for some organosilanes. A summary of these measured data is in
the table below.
predictions are also presented for comparison with the measured data.
Table Measured data and AOPWIN predictions for reaction with hydroxyl
radicals in air.
Rate constantfor reaction with hydroxyl radicals (kOH(cm3/ molecule. sec))
1.28 x 10-12(Sommerlade, 1993)
0.6 x 10-12(AOPWIN)
1.0 x 10-12(Atkinson, 1991)
8.5 x 10-13(Tuazon, 2000)
1.19 x 10-12(Sommerlade, 1993)
0.9 x 10-12(AOPWIN)
1.4 x 10-12(Atkinson, 1991)
1.26 x 10-12(Sommerlade, 1993)
1.2 x 10-12(AOPWIN)
0.5 x 10-12(Atkinson, 1991)
1.5 x 10-12(AOPWIN)
1.6 x 10-12(Atkinson, 1991)
7.2 x 10-12(AOPWIN)
8.1 x 10-13(Tuazon, 2000)
3.95 x 10-12(Sommerlade, 1993)
3.9 x 10-12(AOPWIN)
7.2 x 10-13(Tuazon, 2000)
The measured values from Sommerlade (1993) and Atkinson (1991) are
roughly in agreement, and correlate well with the predicted values.
Indeed, the data from these two studies were used in the training set
for the AOPWIN program.
The measured values from Tuazon (2000) indicate slightly lower
rates of reaction for the silanols compared to the AOPWIN predictions
and the measured value from Sommerlade (1993).
measured value for dimethylsilanediol
(the silanol hydrolysis product of the registration
substance) is used in the exposure assessment as a worst case.
EPA, 2010. US Environmental Protection Agency.AOPWIN
program v1.92a (September, 2010)
(2016). European Chemicals Agency. Guidance on information requirements
and chemical safety assessment Chapter R.16: Environmental Exposure
Estimation. Version: 3.0, February 2016.
et al. (1993). Product Analysis and Kinetics of the Gas-Phase Reactions
of Selected Organosilicon Compounds with OH Radicals Using a Smog
Chamber-Mass Spectrometer System. Environ. Sci. Technol. 1993, 27,
E C, Aschmann S M and Atkinson R (2000) Atmospheric Degradation of
Volatile Methyl-Silicon Compounds Environmental Science and Technology,
Vol. 34, No. 10, 1970-1975
R. 1991. Kinetics of the Gas-Phase Reactions of a Series of
Organosilicon Compounds with OH and NO3 Radicals and O3 at 297 +/- 2 K.
Environ. Sci. Technol. 25(5):863-866.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
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