Registration Dossier

Physical & Chemical properties

Endpoint summary

Administrative data

Description of key information

Additional information

The substance, chloro(dimethyl)vinylsilane, 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 Section 1.4.1 of the CSR.

In contact with water, chloro(dimethyl)vinylsilane hydrolyses very rapidly (half-life <1 minute at 25°C and pH 4, 7 and 9) to produce dimethyl(vinyl)silanol and hydrochloric acid according to the following equation:

(CH3)2Si(CH=CH2)Cl + H2O → (CH3)2Si(CH=CH2)(OH) + HCl

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, dimethyl(vinyl)silanol, are assessed instead.

The silanol hydrolysis product, dimethyl(vinyl)silanol, may undergo condensation reactions in solution to give siloxane dimers (CAS No: 2627-95-4, 1,1,3,3-tetramethyl-1,3-divinyldisiloxane) 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.

The condensation reactions of monosilanols may be modelled as an equilibrium between monomer and dimer. The reaction is reversible unless the dimer concentration exceeds its solubility; in this case, the dimer forms a separate phase, driving the equilibrium towards the dimer. For dimethyl(vinyl)silanol, a solution at 100 mg/l (the highest concentration often used in ecotoxicity tests) is predicted to contain >99.9% monomer. At loadings above about approximately 250 mg/l the concentration of the dimer is predicted to exceed its solubility, resulting in formation of a separate phase. In addition, the dimer is expected to have a high volatility from water and this may cause losses from water under some conditions. Further information is given in a supporting report (PFA 2013am) attached in Section 13.

The saturation concentration in water of the silanol hydrolysis product, dimethyl(vinyl)silanol, is therefore limited by condensation reactions to approximately 300 mg/l. However, it is soluble in water (calculated solubility is 3700 mg/l at 20°C using a QSAR method) with a predicted low log Kow of 1.5. It is not surface active and the first dissociation constant of dimethyl(vinyl)silanol is predicted to be around pKa = 11. The silanol hydrolysis product is much less volatile than the parent substance (predicted vapour pressure = 250 Pa at 25°C).

Chloro(dimethyl)vinylsilane is a liquid at standard temperature and pressure, with a measured melting point of <-20°C, and a measured boiling point of 84 ± 1°C. It has a measured relative density of 0.89218 at 20°C and measured vapour pressure values of 9500 Pa at 20°C, 12000 Pa at 25°C, 15000 Pa at 30°C, 22000 Pa at 40°C and 32000 Pa at 50°C.

Chloro(dimethyl)vinylsilane is classified for flammability in accordance with Regulation (EC) No 1272/2008 as highly flammable liquid on the basis of a measured flash point of -14.3°C and a measured boiling point of 84°C. It has a measured self-ignition temperature of 293°C, and is not explosive and not oxidising on the basis of chemical structure.