Registration Dossier
Registration Dossier
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EC number: 233-054-0 | CAS number: 10026-04-7
Endpoint summary
Administrative data
Description of key information
The substance, silicon tetrachloride, is not stable in water, which affects the approach to the determination of physicochemical properties. The significance of this for read-across is discussed in relevant sections.
Silicon tetrachloride is a liquid at standard temperature and pressure, with a melting point of approximately -70°C at 1013 hPa and a boiling point of 57.3°C at 1013 hPa. It has a density value of 1.48 g/cm3 at 20°C and a viscosity of 0.48 mPa.s at 20°C. The submission substance is a highly volatile liquid with a vapour pressure of 29200 Pa at 20°C.
The substance is classified as non-flammable on the basis that the molecule contains no elements capable of propagating a flame. It does not self-ignite below 650°C, is not explosive and is not oxidising based on structural examination.
In contact with water, silicon tetrachloride reacts very rapidly (half-life of <1 minute at pH 4, pH 7 and pH 9 and 1.5°C) to produce silicic acid and hydrochloric acid according to the following equation:
SiCl4 + 4H2O → Si(OH)4 + 4HCl
Therefore, requirements for testing of water-based physicochemical properties for the submission substance are waived on the basis of instability in water. The properties of the silanol hydrolysis products, silicic acid is assessed instead.
Monosilicic acid exists only in dilute aqueous solutions and readily condenses at concentrations above approximately 100-150 mg/L as SiO2, to give a dynamic equilibrium between monomer, oligomers and insoluble amorphous polysilicic acid. Silicic acid is expected to have negligible vapour pressure and not surface active. log Kow is not relevant for inorganic compound such as silicic acid.
Silicic acid does not undergo significant dissociation within the environmentally-relevant pH range; the first dissociation constant is approximately 10.
Additional information
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