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3-Aminopropyl(triethoxy)silane is a liquid at standard temperature and pressure, with a melting point of <-20°C, and a predicted boiling point of 230°C. It has a predicted density of 0.95 g/cm3 at 20°C, a predicted kinematic viscosity of 1.8 mm2/s at 20°C and a predicted vapour pressure of 8 Pa at 25°C.

The substance is not classified for flammability according to Regulation (EC) No. 1272/2008 on the basis of a measured flash point of 98°C at 1013 hPa and a predicted boiling point of 230°C. It has a measured auto-ignition temperature of 270°C at 1009.3 to 1010.7 hPa and is not explosive and not oxidising on the basis of chemical structure.

In contact with water, the substance hydrolyses rapidly (half-lives of 0.8 h at pH 5, 8.5 h at pH 7 and 0.15 h at pH 9 and 24.7°C) resulting in the formation of 3-aminopropylsilanetriol and ethanol according to the following equation:

H2N(CH2)3Si(OCH2CH3)3 + 3H2O ¿ H2N(CH2)3Si(OH)+ 3CH3CH2OH

 

Therefore, requirements for testing of water-based physicochemical properties for the substance are waived on the basis of instability in water.

However, the properties of the parent submission substance have been estimated using appropriate QSAR methods. The unionised form of the substance 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 parent submission substance. 3-Aminopropyl(triethoxy)silane has a predicted water solubility value of 1.7E+04 mg/L at 20°C.

Ethanol is miscible with water, has low log Kow (-0.3) and high vapour pressure (7910 Pa at 25°C).

 

The saturation concentration in water of the silanol hydrolysis product, 3-aminopropylsilanetriol, is 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 (vapour pressure = 2.5E-04 Pa at 25°C, predicted). 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.

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