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EC number: 246-467-6
CAS number: 24801-88-5
substance, triethoxy(3-isocyanatopropyl)silane, 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
is a liquid at standard temperature and pressure, with a measured
melting point of <-100°C at 1013 hPa and a measured boiling point of
242°C at 1013 hPa. It has a measured relative density of 1.00067 at
20°C, measured kinematic viscosity of 1.6 mm2/s at 20°C
and approximately 1.2 mm2/s at 40°C. The substance has
measured vapour pressures of 2 Pa at 20°C, 3.2 Pa at 25°C and 24 Pa at
substance is not classified for flammability according to Regulation
(EC) No 1272/2008 on the basis of a measured flash point of 106.5°C at
1013 hPa and a measured boiling point of 242°C at 1013 hPa. It has a
measured auto-ignition temperature of 255°C and is not explosive and not
oxidising on the basis of chemical structure.
submission substance, triethoxy(3-isocyanatopropyl)silane,
has two hydrolysable groups, triethoxy (-OCH3CH2)
and isocyanate (-N=C=O). In contact with water, the isocyanate
group is expected to hydrolyse very rapidly, for example the hydrolysis
half-lives of 2,2,4- (or 2,4,4)-trimethylhexane-1,6-diisocyanate (CAS
32052-51-0) were measured in accordance with OECD 111 and in compliance
with GLP (Lange 2013). Very rapid hydrolysis following pseudo-first
order kinetics was observed; hydrolysis half-lives of 3.81 min at pH 4,
4.88 min at pH 7 and 1.93 min at pH 9 and 20°C were determined.
Similarly, n-butyl isocyanate (CAS 111-36-4) was reported to undergo
complete hydrolysis in water within a few minutes at 20°C (OECD 2005).
For the submission
substance, this means very rapid hydrolysis to form
3-aminopropyltriethoxysilane (CAS 919-30-2) as an intermediate
hydrolysis product and carbon dioxide. The hydrolysis half-lives of
3-aminopropyltriethoxysilane have been measured in accordance with OECD
111 to be 0.8 h at pH 5, 8.5 h at pH 7, and 0.15 h at pH 9 and 24.7°C.
The ultimate silanol hydrolysis product under dilute conditions is
3-aminopropylsilanetriol. The other product of hydrolysis is ethanol
according to the following equation:
+ 4H2O → NH2(CH2)3Si(OCH2CH3)3 +
CO2 → H2N(CH2)3Si(OH)3 + 3CH2CH3OH
requirements for testing of water-based physicochemical properties for
the submission substance are waived on the basis of instability in water.
properties of the intermediate hydrolysis product
3-aminopropyltriethoxysilane have been estimated using appropriate QSAR
unionised form of the intermediate hydrolysis product has a predicted
log Kow of 1.7. In solution, the amine group will protonate;
therefore,the estimated log Kow for the unionised form
was corrected for ionisation using the equation CORR = 1/1 +10A(pH-pKa)
[where A = 1 for acids, -1 for bases; pH = pH-value of the
environment; pKa = acid/base dissociation constant]. Log Kow values
of -4 at pH 2, -4 at pH 4, -1.3 at pH 7 and 0.7 at pH 9 were determined
for the intermediate hydrolysis product. 3-Aminopropyl(triethoxy)silane
has a predicted water solubility value of 1.7E+04 mg/L at 20°C.
is miscible with water, has low log Kow (-0.3) and high
vapour pressure (7910 Pa at 25°C).
The ultimate silanol hydrolysis
product, 3-aminopropylsilanetriol, 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 between the monomer, dimer and
tetramer of 3-aminopropylsilanetriol. 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 3-aminopropylsilanetriol, 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, 3-aminopropylsilanetriol, is
therefore limited by condensation reactions to approximately 1000 mg/L.
However, it is very hydrophilic (calculated solubility is 1.0E+06 mg/L
using a QSAR method) and the ionised form of the silanol hydrolysis
product have predicted log Kow of -4 at pH 2, pH 4 and pH 7.
At pH 9, the predicted log Kow is -3.5.
3-Aminopropylsilanetriol is not
surface active and is much less volatile than the parent substance with
a predicted vapour pressure of 2.5E-04 Pa at 25°C. The first
dissociation constant of a structurally analogous silanetriol
(phenylsilanetriol) has been reported to be around pKa of 10. The amine
group has a pKa of approximately 9.5 based on available data.
The by-product of the isocyanate
hydrolysis, carbon dioxide, is exempt from registration under REACH
Article 2(7) because (a) it is a substance with sufficiently known
information and (b) it is considered to cause minimum risk due to its
intrinsic properties. It is therefore not assessed in this CSA.
Lange (2013). Lange, J.
(2013). Vestanat TMDI - hydrolysis as a function of pH. Dr. U.
Noack-Laboratorien, Sarstedt (Germany). Test report. Testing laboratory:
Dr. U. Noack-Laboratorien, Sarstedt (Germany). Report no.: CPH14411.
Owner company: Evonik lndustries AG. Report date: 2013-01-21.
OECD (2005). SIDS Initial
Assessment Report for SIAM 21, Washington, 18-21 October 2005, n-Butyl
isocyanate, CAS 111-36-4.
PFA (2016am). Peter Fisk
Associates, Analogue Report - 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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