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Description of key information

The substance, 3-(trimethoxysilyl)propane-1-thiol is a colourless liquid at standard temperature and pressure, with a measured melting point of < -80 °C, and a predicted boiling point of 200 °C. It has a relative density of 1.015 at 25 °C and a predicted vapour pressure of 8.1 Pa at 25 °C. The substance has a predicted viscosity of 1.8 mm2/s at 20°C.


The substance is not classified for flammability according to Regulation (EC) No. 1272/2008 on the basis of a measured flash point of 95 °C and a predicted boiling point of 200 °C. It has a measured auto-ignition temperature of 243 °C and is not explosive and not oxidising on the basis of structural examination.


In contact with water, 3-(trimethoxysilyl)propane-1-thiol reacts rapidly (half-life of 0.2 h at pH 4, 0.3 h at pH 5, 2.6 hours at pH 7 and 0.1 hours at pH 9, between 20-25 °C) to produce 3-(trihydroxysilyl)propanethiol and methanol according to the following equation:




Therefore, requirements for testing of water-based physicochemical properties for the substance are waived on the basis of instability in water. The properties of the hydrolysis products, 3-(trihydroxysilyl)propanethiol and methanol are assessed instead.


However, the key physicochemical properties of 3-(trimethoxysilyl)propane-1-thiol was predicted with the use of a validated QSAR estimation method. The substance has a predicted log Kow value of 1.7 at pH 7 and 20 °C, and water solubility value of 2800 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 2004).


The saturation concentration in water of the silanol hydrolysis product, 3-(trihydroxysilyl)propanethiol is limited by condensation reactions that can occur over time at loadings above approximately 1000 mg/l. However, it is very hydrophilic (calculated solubility is 1.0E+06 mg/l at 20 °C using a QSAR method) and has a low log Kow (-1.4 at pH 7 and 20 oC, predicted). It is not expected to be surface active and it is much less volatile than the parent substance with a predicted vapour pressure of 1.1E-04 Pa at 25°C. The silanol hydrolysis product is not expected to undergo significant dissociation within the environmentally-relevant range. The first dissociation constant of a structurally analogous silanetriol (phenylsilanetriol) has been reported to be around pKa of 10.



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





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