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EC number: 451-620-7
CAS number: 352230-22-9
Phototransformation in air.
Half-life for reaction with OH
Constituent 1: 4.8E-12
cm3/molecule.sec (half-life 3.3 days)
cm3/molecule.sec (half-life 1.8 days)
measured data are available for the submission substance.
AOPWIN program (v1.92, EPA 2010) has been used to obtain values of the
rate constant kOH for reaction of the constituents of
the submission substance and
their 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:
(d-1) = kOH (cm3/molecule.sec) x
OH Concair (molecules/cm3) x 24 x 3600
(d) = 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 E+05 OH molecules/cm3
concentration of hydroxyl radicals in air of 5E+05 OH 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).
The results are given in the
table below for the constituents of the substance.
Table 4.1.2: Results of
photodegradation in air calculations
Constituent 1- 3,3-Diphenylhexamethyltrisiloxane
Constituent 2 - 3,3,5,5-Tetraphenylhexamethyltetrasiloxane
Available data for other
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 4.1.3. Measured data and
AOPWIN predictions for reaction with hydroxyl radicals in air.
Rate constant for reaction with hydroxyl radicals (kOH (cm3/ molecule. sec))
1.28E-12 (Sommerlade et al., 1993)
1.0E-12 (Atkinson, 1991)
8.5E-13 (Tuazon, 2000)
1.19E-12 (Sommerlade et al., 1993)
1.4E-12 (Atkinson, 1991)
1.26E-12 (Sommerlade et al., 1993)
0.5E-12 (Atkinson, 1991)
1.6E-12 (Atkinson, 1991)
8.1E-13 (Tuazon, 2000)
3.95E-12 (Sommerlade et al., 1993)
7.2E-13 (Tuazon, 2000)
measured values from Sommerlade et al. (1993) and Atkinson (1991)
are in sufficient 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.
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 et al. (1993).
2010. US Environmental Protection Agency. AOPWIN program v1.92a
ECHA (2016). REACH Guidance on
Information Requirements and Chemical Safety Assessment Chapter R16:
Environmental Exposure Assessment Version: 3.0. February 2016.
R.16-3.2.2 Photochemical reactions in the atmosphere
R., Parlar, H., Wrobel, D. and Kochs, P.(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 (12), 2435-2440.
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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