Dichloro(3-chloropropyl)methylsilane

Endpoint summary

Description of key information

Dichloro(3-chloropropyl)methylsilane is a liquid at standard temperature and pressure, with a measured melting point of <-100°C and a predicted boiling point of 171°C. It has a measured density greater than that of water (1.2 g/cm³at 20°C) and moderate viscosity (1.4 mm²/s (static) at 20°C, prediction). It has a predicted vapour pressure of 83 Pa at 25°C.

The substance is not classified as flammable on the basis of a measured flash point of 73°C and boiling point of 171°C. It has a measured auto-ignition temperature of 225°C, is not explosive and is not oxidising on the basis of chemical structure.

In contact with water dichloro(3-chloropropyl)methylsilane is expected to react very rapidly (based on read-across from a related substance; half-life <1 min at 25°C and pH 4, 7 and 9) according to the following equation to form (3-chloropropyl)methylsilanediol and hydrochloric acid:

ClCH₂CH₂CH₂Si(CH₃)Cl₂+ 2H₂O → ClCH₂CH₂CH₂Si(CH₃)(OH)₂+ 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, (3–chloropropyl)methylsilanediol, have been predicted instead.

The silanol hydrolysis product, (3-chloropropyl)methylsilanediol, 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. The condensation reactions may be modelled as an equilibrium between monomer, dimer, trimer and tetramer, with the linear tetramer cyclising to the thermodynamically stable cyclic tetramer. The reactions are reversible as long as the concentrations are low and all species remain soluble; thus, a dynamic equilibrium is established. At higher concentrations one or more of the oligomers may exceed their solubility limit and form a separate phase, driving the equilibrium towards the oligomer/polymers. At loadings below 1000 mg/l of (3-chloropropyl)methylsilanediol, the soluble monomer is expected to predominate in solution (>99%), with small amounts of dimer and oligomers. Condensation reactions are expected to become important at loadings above about 1000 mg/l (or lower under some circumstances) causing the formation of insoluble polymeric particles and gels over time.

Further information is given in a supporting report (PFA 2016am) attached in Section 13 of the IUCLID dataset.

The saturation concentration in water of the silanol hydrolysis product, (3-chloropropyl)methylsilanediol, is therefore limited by condensation reactions to approximately 1000 mg/l. However, it is very hydrophilic (calculated solubility is 60 000 mg/l at 20°C using a QSAR method) with a predicted low log Kow of 0.8. It is not surface active. The silanol hydrolysis product is much less volatile than the parent substance (predicted vapour pressure 0.021 Pa at 25°C).