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EC number: 213-650-7
CAS number: 998-30-1
Half-life for hydrolysis: approximately 0.7 h at 20 - 25°C
A half-life of 0.7 hours for hydrolysis of the triethoxy group was
obtained for the substance using an appropriate calculation method. The
result is considered to be reliable.
The initial hydrolysis products are silanetriol and ethanol.The
Si-H bond may also be unstable, resulting in further hydrolysis toSi(OH)4.Silanols
may undergo condensation reactions to form siloxane dimers, oligomers
and polymers. In the case of triethoxysilane, where no organic
side-chains are present, rapid condensation to inorganic siloxanes and
finally silica is expected. The precise rate of this condensation and
the species present are dependent on conditions.
A QSAR that is currently being developed (Peter Fisk Associates
2012c) predicts half-lives at 20-25°C of 0.1 h at pH 4, 0.2 h at pH 5
and 0.02 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 uncatalyzed 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 on:
t1/2(pH 2) = t1/2(pH 4) / 100
As a worst-case it can therefore be considered that the half-life
for triethoxysilane 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 equation:
DT50(XºC) = DT50(T) x e(0.08.(T-X))
Where T = temperature for which data are available and X = target
For triethoxysilane 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
The initial hydrolysis products are silanetriol and ethanol.
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