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Physical & Chemical properties

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3-(Trimethoxysilyl)propiononitrile is a liquid at standard temperature and pressure, with a measured melting point of <-46°C at 1013 hPa, and a predicted boiling point of 210°C. It has a predicted density of 0.97 g/cm3 at 20°C, a predicted kinematic viscosity of 2.0 mm2/s at 20°C and a predicted vapour pressure of 4.7 Pa at 25°C.

A flash point of 60°C and a predicted boiling point of 210°C have been obtained; further sustained combustibility testing found that the substance is not considered to support combustion. Therefore, the substance does not meet the criteria for classification as a flammable liquid and vapour according to the criteria of Regulation (EC) No. 1272/2008.

The substance has a measured auto-ignition temperature of 380°C at 1024.1 to 1030.7 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 0.1 h at pH 4, 1.1 h at pH 7 and 0.02 h at pH 9 and 20-25°C) resulting in the formation of 3-(trihydroxysilyl)propiononitrile (CAS 182156-21-4) and methanol (CAS 67-56-1) according to the following equation:

N=CCH2CH2Si(OMe)3+ 3H2O ¿ N=CCH2CH2Si(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 substance has a predicted log Kow value of 0.2 and a predicted water solubility value of 1.3E+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-(trihydroxysilyl)propiononitrile, 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 has a predicted log Kow of -2.9. 3-(Trihydroxysilyl)propiononitrile is not surface active and is much less volatile than the parent substance (vapour pressure = 6.7E-05 Pa at 25°C, predicted). The first dissociation constant of a structurally analogous silanetriol (phenylsilanetriol) has been reported to be around pKa of 10.

Reference:

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

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