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Description of key information

The substance, 3-(triethoxysilyl)propanethiol, CAS 14814-09-6; EC No. 238-883-1 is a liquid at standard temperature and pressure, with a glass transition temperature of -141°C at 1013 hPa and a measured boiling point of 236°C at 1013 hPa. It has a measured relative density of 0.983 at 20°C and a predicted vapour pressure of 2.9 Pa at 25°C.

3-(Triethoxysilyl)propanethiol has a predicted water solubility value of 82 mg/L at 20°C and a measured log Kow of 2.7 at 20°C and pH 7.6 -7.7.

The substance is not classified for flammability according to Regulation (EC) No. 1272/2008 on the basis of a measured flash point of 89.5°C at 1013 hPa and a measured boiling point of 236°C at 1013 hPa. It has a measured auto-ignition temperature of 205°C at 998-1011 hPa and is not explosive and not oxidising on the basis of structural examination.

In contact with water, 3-(triethoxysilyl)propanethiol reacts moderately rapidly (half-life of 3.2 minutes at pH 4, 32.1 hours at pH 7, 4.69 hours at pH 9 and 20°C) to produce 3-(trihydroxysilyl)propanethiol and ethanol, CAS 64-17-5; EC No. 200-578-6 according to the following equation:

HSCH2CH2CH2Si(OCH3CH2)3+ 3H2O → HSCH2CH2CH2Si(OH)+ 3CH3CH2OH

 

Due to the moderate hydrolysis of 3-(triethoxysilyl)propanethiol in contact with water, the key physicochemical properties of the hydrolysis products are presented below.

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-(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, 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. Similarly, the thiol group has a calculated pKa of approximately 10.

 

 

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