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EC number: 242-272-5
CAS number: 18395-30-7
Hydrolysis: half-life at 20-25°C approximately 4.1 h at pH 7, 0.2 h at pH 4, 0.1 h at pH 9.
A half-life value of approximately 4.1 h at
20-25°C and pH 7 was obtained using an accepted validated QSAR method
(Peter Fisk Associates 2012a). The result is considered to be reliable
and has been assigned as key study.
kobs= k0+ kH3O+[H3O+]
+ kOH-[OH-] + ka[acid] + kb[base]
At extremes of pH and under standard hydrolysis test conditions, it is
reasonable to suggest that the rate of hydrolysis is dominated by either
the hydronium or hydroxide catalysed mechanism. This is supported by
studies for various organosilicon compounds in which calculation of kH3O+
and kOH- from the experimental results at pH 4 and 9,
respectively, resulted in reasonable estimates of the half-life at pH 7.
Therefore, at low pH:
At pH 4 [H3O+]=10-4mol dm-3and
at pH 2 [H3O+]=10-2mol dm-3;
therefore, kobs at pH 2 should be approximately 100 times
greater than kobs at pH 4.
The half-life of a substance at pH 2 is calculated based on:
t1/2(pH 2) = t1/2(pH 4) / 100
The calculated half-life of trimethoxy(2 -methylpropyl)silane at pH 2 is
therefore 0.002 hours (0.12 seconds). However, it is likely that factors
such as diffusion become rate-determining when the half-life is less
than 5-10 seconds. As a worst-case it can therefore be considered that
the half-life for trimethoxy(2 -methylpropyl)silane at pH 2 and 20-25°C
is approximately 5 seconds. Reaction rate increases with temperature
therefore hydrolysis will be faster at physiologically relevant
temperatures compared to standard laboratory conditions. Under ideal
conditions, hydrolysis rate can be recalculated according to the
DT50(XºC) = DT50(T) * e(0.08.(T-X))
Where T = temperature for which data are available and X = target
Thus, for trimethoxy(2 -methylpropyl)silane the hydrolysis half-life at
37.5ºC and pH 7 (relevant for lungs and blood) is 1.5 hours. At 37.5ºC
and pH 2 (relevant for conditions in the stomach following oral
exposure), it is not appropriate to apply any further correction for
temperature to the limit value and the hydrolysis half life is therefore
approximately 5 seconds.
products are (2-methylpropyl)silanetriol and methanol.
Hydrolysis of the read-across substance silane,
trimethoxy(1,1,2-trimethylpropyl)- (CAS 142877-45-0)
Data for the substancesilane,
trimethoxy(1,1,2-trimethylpropyl)-(CAS 1428777-45-0) are
read-across to the submission substance trimethoxy(2-methylpropyl)silane
for appropriate endpoints (see Section 1.4).The silanol
hydrolysis product of the two substances is relevant to this
read-across, as discussed in the appropriate Sections of the CSR for
For silane, trimethoxy(1,1,2-trimethylpropyl)-, hydrolysis half-lives at
25°C of 1.1 h at pH 4, approximately 73 h at pH 7 and 0.9 h at pH 9 were
determined using a validated QSAR estimation method.
Hydrolysis of the read-across substance triethoxyisobutylsilane
Data for the substancetriethoxyisobutylsilane(CAS
17980-47-1) are read-across to the submission substance
trimethoxy(2-methylpropyl)silane for appropriate endpoints (see Section
1.4).The silanol hydrolysis product of the two substances is
relevant to this read-across, as discussed in the appropriate Sections
of the CSR for each endpoint.
For triethoxyisobutylsilane, hydrolysis half-lives at 25°C of 0.7 h at
pH 4, 30 h at pH 7 and 0.4 h at pH 9 were determined using validated
QSAR estimation method.
The half-lives at pH 2 and 25°C, at pH 7 and 37.5°C and at pH 2 and
37.5°C may be calculated in the same way as for the registration
substance above. This gives a half-life of 0.007 h (25 seconds) at pH 2
and 25°C, and 11 h at pH 7 and 37.5°C. At pH 2 and 37.5°C, the
hydrolysis half-life is 0.0025 h (9 seconds).
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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