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Physical & Chemical properties

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Description of key information

3-(Trimethoxysilyl)propylamine is a liquid at standard temperature and pressure, with a measured melting point of <-80°C at 1013 hPa, and a measured boiling point of 198.4°C. It has a measured relative density of 1.014 at 20°C, a measured kinematic viscosity of 1.77 mm2/s at 20°C and a predicted vapour pressure of 21 Pa at 25°C.

The substance is classified for flammability according to Regulation (EC) No. 1272/2008 on the basis of a measured flash point of 87°C at 1013 hPa and a measured boiling point of 198.4°C. It has a measured auto-ignition temperature of 314°C at 957.3 to 975.1 hPa), and it is not explosive and not oxidising on the basis of chemical structure.

In contact with water, the substance hydrolyses rapidly (half-lives of 0.2 h at pH 4, 2.6 h at pH 7 and 0.1 h at pH 9 and 20-25°C) resulting in the formation of 3-aminopropylsilanetriol (CAS 58160-99-9) and methanol (CAS 67-56-1) according to the following equation:

H2N(CH2)3Si(OCH3)3+ 3H2O ¿ H2N(CH2)3Si(OH)+ 3CH3OH

 

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 0.2. 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, -2.8 at pH 7 and -0.8 at pH 9 were determined for the parent submission substance. 3-(Trimethoxysilyl)propylamine has a predicted water solubility value of 5.7E+05 mg/L at 20°C.

Methanol is miscible with water, has low log Kow (-0.82 to -0.64) and high vapour pressure (12790 Pa at 20°C) (OECD 2004a).

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.

Reference:

OECD (2004a): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 18 - 20 October 2004, Methanol, CAS 67-56-1).

Additional information