3-(trimethoxysilyl)propylamine

Endpoint summary

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 at 1013 hPa. 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 not 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 at 1013 hPa. 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 is predicted to 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)₃ + 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 K_ow of 0.2. In solution, the amine group will protonate; therefore, the estimated log K_ow for the unionised form was corrected for ionisation using the equation: CORR = 1/1 +10^A(pH-pKa) [where; A = 1 for acids or -1 for bases, pH = pH-value of the environment and pK_a = acid/base dissociation constant].

 

Log K_ow 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 K_ow (-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 K_ow of -4 at pH 2, 4 and 7, and at pH 9, the predicted log K_ow 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 as a pK_a of approximately 10. The amine group has a pK_a of approximately 10 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).