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EC number: 220-449-8
CAS number: 2768-02-7
The results of pH 4.0 and pH 9.0
show that the test substance was very unstable in aqueous test solutions
and starts to hydrolyse immediately after being dissolved in the buffer
(no test substance could be detected in the samples at the first time
point; which was immediately after starting the test).
At pH 7.0 the analytical results
indicate that the degradation of the test substance was more than 50%
after 2.4 hours. It can be concluded that the estimated half-life times
at pH 4.0, pH 7.0 and pH 9.0 are shorter than one day under
representative environmental conditions (25°C). Therefore, no further
testing was necessary at these pH values.
The results for individual
measurements are in Table 1 below.
Table 1: Results of the
Initial concentration [µg/mL]
Concentration measured after 2.4 hours incubation [µg/mL]
Concentration measured after 5 days incubation [µg/mL]
Hydrolysis reaction after 2.4 hours incubation [%]
n.d. = not detected
The stability of the test
substance in buffer solution pH 4 and pH 9 was very low. The test item
could not be detected in any of the sample solutions.
Hydrolysis: 0.04 h at pH 4, 0.1 h
at pH 7 and 0.004 h at pH 9 and 20-25°C (QSAR)
Hydrolysis half-lives at 20
-25°C of 0.04 h at pH 4, 0.1 h at pH 7 and 0.004 h at pH 9 were
determined for the substance using a validated QSAR estimation method.
Also, in a preliminary study conducted in accordance with OECD 111,
hydrolysis half-lives of <10 minutes at pH 4, <2.4 h at pH 7 and <10
minutes at pH 9 and 50°C were determined for the substance. Both results
were considered to be reliable and used as weight of evidence. A
half-life of 0.24 h at pH 7 and 23°C, from a study of non-assignable
reliability adds further weight of evidence to the very rapid hydrolysis
potential of the submission substance.
As the hydrolysis reaction may be
acid or base catalysed, the rate of reaction is expected to be slowest
at around 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
Therefore, at low pH:
kobs ˜ kH3O+[H3O+]
At pH 4 [H3O+]
= 10-4 mol dm-3 and at pH 2 [H3O+]
= 10-2 mol dm-3; therefore, kobs at pH
2 should be approximately 100 times greater than kobs at pH
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 the
substance at pH 2 is therefore less than 2 seconds. However, it is not
appropriate or necessary to attempt to predict accurately when the
half-life is less than 5-10 seconds. As a worst-case it can therefore be
considered that the half-life of the substance 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)
Where T = temperature for which
data are available and X = target temperature.
Thus, for trimethoxy(vinyl)silane
the hydrolysis half-life at 37.5ºC and pH 7 (relevant for lungs and
blood) is approximately 2 minutes. 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.
The hydrolysis products in
this case are vinylsilanetriol (CAS 143-48-6) and methanol (CAS 67-56-1;
EC No. 200-659-6).
The hydrolysis data for
substances used in this dossier for read-across purposes for other
endpoints are now discussed.
Hydrolysis of the
read-across substance trichloro(vinyl)silane (CAS 75-94-5; EC No. 200-917-8)
Data for the substance,
trichloro(vinyl)silane (CAS 75-94-5) are read-across to the submission
substance trimethoxy(vinyl)silane for toxicity to microorganisms
endpoint. The silanol hydrolysis product and the rate of hydrolysis of
the two substances are relevant to this read-across, as discussed in the
appropriate section for the endpoint.
For trichloro(vinyl)silane, hydrolysis
half-lives at 1.5°C of <1 minute at pH 4, pH 7 and pH 9 were read-across
from trichloro(methyl)silane in accordance with OECD Test Guideline 111
(Dow Corning Corporation 2001).
hydrolysis products are vinylsilanetriol and hydrochloric acid.
Hydrolysis of the
read-across substance diethoxy(dimethyl)silane (CAS 78-62-6; EC No. 201-127-6)
Data for the substance,
diethoxy(dimethyl)silane (CAS 78-62-6) are read-across to the submission
substance trimethoxy(vinyl)silane for basic toxicokinetics endpoint. The
rate of hydrolysis of the two substances are relevant to this
read-across, as discussed in the appropriate section for the endpoint.
For diethoxy(dimethyl)silane, hydrolysis
half-lives at 20-25°C of 0.3 hours at pH 4, 5.5 hours at pH 7 and 0.3
hours at pH 9 were determined using validated QSAR estimation methods.
hydrolysis products are dimethylsilanediol and ethanol.
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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