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EC number: 236-828-6
CAS number: 13501-76-3
Hydrolysis half-life: 3.8 hours at pH 7 and 25°C
reliable study according to OECD 111 is available for the substance
half-life of 9.5 hours for hydrolysis of
(3-chloropropyl)diethoxymethylsilane was obtained using an appropriate
calculation method. The result is considered to be reliable.
initial hydrolysis products are (3-chloropropyl)methylsilanediol and
ethanol. Silanols may undergo condensation reactions to form siloxane
dimers, oligomers and polymers. The precise rate of this condensation
and the species present are dependent on conditions.
A QSAR that is currently being developed (Peter Fisk
Associates 2012) predicts half-lives at 20-25°C of 0.4 h at pH 4, 0.4 h
at pH 5 and 0.2 h at pH 9. As the hydrolysis reaction may be acid or
base catalysed, the rate of reaction is expected to be slowest at pH 7
and increase as the pH is raised or lowered.
For an acid-base catalysed reaction in buffered solution,
the measured rate constant is a linear combination of terms describing
contributions from the uncatalysed reaction as well as catalysis by
hydronium, hydroxide, and general acids or bases.
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 pH2 [H3O+]=10-2mol dm-3;
therefore, kobsat pH 2 should be approximately 100 times
greater than kobsat pH 4.
The half-life of a substance at pH 2 is calculated based
t1/2(pH 2) = t1/2(pH 4) / 100
As a worst-case it can therefore be considered that the
half-life for (3-chloropropyl)diethoxymethylsilane 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) x
Where T = temperature for which data are available and X
= target temperature.
(3-chloropropyl)diethoxymethylsilane the hydrolysis half-life at 37.5ºC
and pH2 (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
The initial hydrolysis products are
(3-chloropropyl)methylsilanediol and ethanol.
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