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EC number: 220-449-8
CAS number: 2768-02-7
trimethoxy(vinyl)silane (CAS 2768-02-7; EC No. 220-449-8), is not stable
in water, which affects the approach to the determination of
physicochemical properties. The significance of this for read-across is
discussed in relevant sections.
Trimethoxy(vinyl)silane is a
liquid at standard temperature and pressure, with a measured melting
point of -97°C at 1013 hPa and a measured boiling point of 123°C at 1013
hPa. It has a predicted density of 0.94 g/cm3 at 20°C and a
predicted kinematic viscosity of 0.7 mm2/s at 20°C. The
submission substance has measured vapour pressure values of 640 Pa at
10°C, 1190 Pa at 20°C and 6000 Pa at 50°C.
The substance is classified for
flammability according to Regulation (EC) No. 1272/2008 on the basis of
a measured flash point of 25.5 - 26°C and a measured boiling point of
123°C at 1013 hPa. It has a measured auto-ignition temperature of 224°C
at 1013 hPa, it is not explosive and not oxidising on the basis of
In contact with water,
trimethoxy(vinyl)silane reacts very rapidly (half-life of 0.1 hours at
pH 7, 0.04 hours at pH 4, 0.004 hours at pH 9 and 20-25°C) to produce
vinylsilanetriol (CAS 143-48-6) and methanol (CAS 67-56-1; EC No.
200-659-6) according to the following equation:
+ 3H2O ¿ CH2=CHSi(OH)3 + 3CH3OH
Therefore, requirements for
testing of water-based physicochemical properties for the substance are
waived on the basis of instability in water. The properties of the
silanol hydrolysis products, vinylsilanetriol and methanol are assessed
instead. However, the water solubility and log Kow of
trimethoxy(vinyl)silane have been predicted to be 3.0E+04 mg/L and 1.1
at 20°C respectively.
is miscible with water, has low log Kow (-0.82 to -0.64) and
high vapour pressure (12790 Pa at 20°C) (OECD 2004).
The silanol hydrolysis product,
vinylsilanetriol, may undergo condensation reactions in solution to give
siloxane dimers, linear and cyclic oligomers and highly cross-linked
polymeric particles (a colloidal suspension of small solid particles
known as a sol) that may over time form an insoluble gel and a dynamic
equilibrium is established. The overall rate and extent of condensation
is dependent on nominal loading, temperature, and pH of the system, as
well as what else is present in the solution.
The condensation reactions of
silanetriols may be modelled as an equilibrium between monomer, dimer,
trimer and tetramer, with the linear tetramer cyclising to the
thermodynamically stable cyclic tetramer. At higher loadings,
cross-linking reactions between the cyclic tetramers may occur. The
reactions are reversible unless the cyclic tetramer concentration
exceeds its solubility; in this case, the cyclic tetramer forms a
separate phase, driving the equilibrium towards the tetramer. At
loadings below 500 mg/L of vinylsilanetriol, the soluble monomer is
expected to predominate in solution (>99%), with small amounts of dimer
and oligomers. Condensation reactions are expected to become important
at loadings above about 1000 mg/L causing the formation of insoluble
polymeric particles and gels over time. Further information is given in
a supporting report (PFA 2016am) attached in Section 13.
The saturation concentration in
water of the silanol hydrolysis product vinylsilanetriol is therefore
limited by condensation reactions to approximately 1000 mg/L. However,
it is very hydrophilic (calculated solubility is 1E+06 mg/L at 20°C
using a QSAR method) with a predicted low log Kow of -2.0. It
is not surface active and is not expected to undergo significant
dissociation within the environmentally-relevant range. The first
dissociation constant of a structurally analogous silanetriol
(phenylsilanetriol, CAS 3047-74-3, EC No. 221-257-7) has been reported
to be around pKa of 10. It is much less volatile than the parent
substance with a predicted vapour pressure of 0.017 Pa at 25°C.
(2004). SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 18
- 20 October 2004, Methanol, CAS 67-56-1
(2016am). Peter Fisk Associates, Silanols and aquatic systems,
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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