Registration Dossier
Registration Dossier
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EC number: 237-041-0 | CAS number: 13596-23-1
Partition coefficient
Administrative data
Link to relevant study record(s)
Description of key information
Log Kow [octachlorotrisilane]: Not relevant
Log Kow [octahydroxytrisilane]: -4 at 20°C (QSAR)
Log Kow [polysilicic acid]: -4 at 20°C (QSAR)
Key value for chemical safety assessment
Additional information
In accordance with Column 2 of REACH Annex VII, the partition coefficient study does not need to be conducted as octachlorosilane and its hydrolysis products are inorganic.
Octachlorotrisilane reacts rapidly with water, generating octahydroxytrisilane and hydrochloric acid. The Si-Si bonds may also react to produce monosilicic acid. At concentrations above about 100-150 mg/L (measured as SiO2equivalents), condensation products of monosilicic acid can also form. At concentrations >100-150 mg/L of SiO2, monomeric monosilicic acid condenses into colloidal particles of polysilicic acid (silica sol) or a highly cross-linked network (silica gel). The condensation rate is dependent on temperature, concentration, and acidity/alkalinity (as in the pH) of the system. A dynamic equilibrium is established between monomeric monosilicic acid, oligomers and insoluble amorphous polysilicicacid. Octahydroxytrisilane is also likely to form condensation products (polyhydroxy-polysilanes) at similar concentrations (in terms of SiO2 equivalents).
The purpose of the log Kow study is to understand the interaction of the substance with water and octanol, which acts as a model for lipids in humans and organisms and for organic carbon in soils and sediments. On the basis of structure and supported by predictions, octahydroxytrisilane have a high affinity with water and low affinity for lipids and organic carbon. Log Kow values of -4 were determined for octahydroxytrisilane and monosilicic acid using a QSAR method. The method has not been validated for inorganic substances but gives an indication of very low log Kow. Neither product has been isolated and the predicted values are included for completeness only.
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