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4,4,13,13-Tetraethoxy-3,14-dioxa-8,9-dithia-4,13-disilahexadecane (CAS 56706-10-6, EC No. 260-350-7, S2) is a light-yellow liquid with a sulfur-like odour at standard temperature and pressure, with a melting point of < -20°C at 1013 hPa. It has a measured relative density of 1.0328 at 20°C, a predicted kinematic viscosity of 2.3 mm2/s at 20°C and a measured vapour pressure of 9 Pa at 20°C and 12 Pa at 25°C. The substance has a predicted log Kow of 5.2 and predicted water solubility of 0.014 mg/l 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 136°C at 1013 hPa and a measured boiling point of 269°C at 1004 hPa. It has a measured auto-ignition temperature of 220°C at 1008 hPa, and is not explosive and not oxidising on the basis of chemical structure.


In contact with water, the substance undergo hydrolysis at a moderate rate (predicted half-lives of 0.8 - 1.2 h at pH 4, 40 - 80 h at pH 7 and 0.5 - 1 h at pH 9 and 20-25°C) resulting in the formation (3-{[3-(trihydroxysilyl)propyl]disulfanyl}propyl)silanetriol and ethanol, according to the following equation:


C18H42O6S2Si2 + 6H2O → C6H18O6S2Si+ 6CH3CH2OH


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-{[3-(trihydroxysilyl)propyl]disulfanyl}propyl)silanetriol, is limited by condensation reactions to approximately 100 mg/l. However, it is very hydrophilic (calculated solubility is 1.0E+06 mg/l using a QSAR method) and has a low log Kow (-3.0 at 20°C, predicted). It is not surface active and is much less volatile than the parent substance with a predicted vapour pressure of 6.3E-12 Pa at 25°C.

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