Registration Dossier
Registration Dossier
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EC number: 253-930-6 | CAS number: 38436-16-7
Endpoint summary
Administrative data
Description of key information
The substance,[2-(perfluorobutyl)ethyl]dichloro(methyl)silaneis not stable in water, which affects the approach to the determination of physicochemical properties. The significance of this for read-across is discussed in the standalone read-across justification document attached in Section 13.
[2-(Perfluorobutyl)ethyl]dichloro(methyl)silaneis a liquid at standard temperature and pressure, with a melting point of -42.3°C, and a measured boiling point of 164.3°C. It has a measured density of 1.481 g/cm3 at 20°C and a predicted vapour pressure of 110 Pa at 25°C.
The substance is not classified for flammability according to Regulation (EC) No 1272/2008 on the basis of a measured flash point of 67 ± 0.5°C and a measured boiling point of 164.3°C. It has a measured auto-ignition temperature of 380°C, and is notoxidising on the basis of chemical structure. [2-(Perfluorobutyl)ethyl]dichloro(methyl)silanewas not explosive under the conditions of an explosivity study based on read-across from a structural analogue in accordance with EU Test Method A.14 and in compliance with a known quality system (ISO 17025).
In contact with water under dilute conditions,[2-(perfluorobutyl)ethyl]dichloro(methyl)silanehydrolyses very rapidly (half-life <1 minute at pH 4, pH 7, pH 9 and 20- 25°C) to produce [2-(perfluorobutyl)ethyl](methyl)silanediol and hydrochloric acid according to the following equation:
C7H7Cl2F9Si + 2H2O → C7H9F9O2Si + 2HCl
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 silanol hydrolysis product, [2-(perfluorobutyl)ethyl]methylsilanediol are assessed instead.
The silanol hydrolysis product, [2-(perfluorobutyl)ethyl](methyl)silanediol, may undergo condensation reactions in solution to give siloxane dimers, linear and cyclic oligomers and a dynamic equilibrium is established. The overall rate and extent of condensation is dependent on nominal loading, temperature and pH of the system, as well as what else is present in the solution. Further information is given in a supporting report (PFA 2013am) attached in Section 13.
The silanol hydrolysis product, [2-(perfluorobutyl)ethyl]methylsilanediol has a predicted water solubility of 2 mg/l at 20°C using a QSAR method and a predicted log Kow of 3.3. It is muchless volatile than the parent substance (vapour pressure = 0.62 Pa at 25°C, predicted).
The surface tension study for [2-(perfluorobutyl)ethyl]dichloro(methyl)silane was waived because the submission substance hydrolyses very rapidly under dilute condition in water. The silanol hydrolysis is considered to be surface active based on a measured surface tension value for [2-(perfluorohexyl)ethyl]silanetriol of <22 mN/m at 20°C and 1 g/l. The presence of fluorocarbon chains may mean that condensation products could have some surface activity. For these reasons, the effective limits of solubility of both the parent substance and monomeric silanol hydrolysis products are very low and all forms of the substance may have a tendency to enrich at surfaces rather than forming stable evenly dispersed solutions.
In the case of this substance, the R group (C7H7F9) contains a perfluorobutyl chain; fluorocarbons have very low solubility in water, relative to hydrocarbons of equivalent chain length (e.g. Horvath 1982), so it would be expected that a substance with this R group would be of low solubility; the corresponding monomeric silanetriol is expected to be surface active based on measured and read across data. The presence of fluorocarbon chains may mean that condensation products could have some surface activity. For these reasons, the effective limits of solubility of both the parent substance and monomeric silanol hydrolysis products are expected to be very low and all forms of the substance may have a tendency to enrich at surfaces rather than forming stable evenly dispersed solutions. These phenomena may limit the extent of hydrolysis under conditions at which the solubility of either parent or oligomer is exceeded. The measured rates presented above relate to dilute conditions. These factors are important in any consideration of aqueous behaviour and properties.
References:
Horvath, A.L., 1982. Halogenated hydrocarbons: solubility-Miscibility with water. CRC press 26 Feb 1982
PFA, 2013am, Peter Fisk Associates, Silanols and aquatic systems, 350.001.003
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