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3-Chloropropyl(dimethoxy)methylsilane is a liquid at ambient temperature and pressure, with a measured melting point of < -100°C at 1013 hPa and a measured boiling point of 187°C at 1013 hPa. It has a measured relative density of 1.0265 at 20°C, a measured kinematic viscosity of 1.2944 mm2/s at 20°C. The substance has a measured vapour pressure values of 67.2 Pa at 20°C, 94.4 Pa at 25°C and 440.3 Pa at 50°C.


The presence of higher concentrations of volatile impurities such as methanol (a hydrolysis product of the substance) can result in a lower flash point. The substance has a measured flash point in the range of 41 - 70°C. It has a measured auto-ignition temperature of 220°C at 1008 -1009 mBar. It is not explosive and not oxidising on the basis of chemical structure.


In contact with water, 3-chloropropyl(dimethoxy)methylsilane reacts rapidly (half-life = 0.1 h at pH 4, 1.3 hour at pH 7 and 0.03 h at pH 9 and 20-25°C, predicted) according to the following equation to produce 3-chloropropyl(methyl)silanediol and methanol:


Cl(CH2)3Si(CH3)(OCH3)2 + 2H2O → Cl(CH2)3Si(CH3)(OH)2 + 2CH3OH


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 hydrolysis products, 3-chloropropyl(methyl)silanediol and methanol, are assessed instead.


However, the properties of the parent substance, 3-chloropropyl(dimethoxy)methylsilane have been predicted using validated QSAR estimation methods. 3-chloropropyl(dimethoxy)methylsilane has predicted log Kow value of 3.2 and predicted water solubility value of 370 mg/l at 20°C.


Methanol is miscible with water, has low log Kow (-0.82 to -0.64) and high vapour pressure (12,790 Pa at 20°C) (OECD 2004a).


The saturation concentration in water of the silanol hydrolysis product, 3-chloropropyl(methyl)silanediol is limited by condensation reactions that can occur over time at loadings about 50 mg/l. However, it is very hydrophilic (calculated solubility is 6.0E+04 mg/l at 20°C using a QSAR method) and has a low log Kow (0.8, predicted). It is not surface active and does not undergo significant dissociation within the environmentally-relevant range. It is much less volatile than the parent substance, with a predicted vapour pressure of 0.018 Pa at 25°C.

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