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[3-(2,3-Epoxypropoxy)propyl]trimethoxysilane is a liquid at standard temperature and pressure, with a melting point of -20°C, and a measured boiling point of 260.4°C. It has a measured relative density of 1.071 at 20°C, a measured kinematic viscosity of 3.43 mm²/s at 20°C and a predicted vapour pressure of 1.1 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 136°C and a measured boiling point of 260.4°C. It has a measured auto-ignition temperature of 236°C at 97.7 to 98.4 kPa and is not oxidising on the basis of chemical structure. [3-(2,3-Epoxypropoxy)propyl]trimethoxysilane was obtained not to exhibit explosivity hazard under the conditions of an EU Method A.14 test method.

In contact with water [3-(2,3-epoxypropoxy)propyl]trimethoxysilane reacts rapidly (half-life of 6.5 hours at pH 7, 0.15 hours at pH 5, 0.13 hours at pH 9 and 24.5°C) to produce [3-(2,3-epoxypropxy)propyl]silanetriol and methanol according to the following equation:

(OCH3)3Si(C3H6OC3H5O) + 3H2O ¿ Si(OH)3(C3H6OC3H5O) + 3CH3OH


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-(2,3-epoxypropoxy)propyl]silanetriol and methanol are assessed instead. However, the log Kow and water solubility of the submission substance was predicted to be 0.5 at 20°C and 1.1E+05 mg/l at 20°C respectively.

Methanol is miscible with water, has low log Kow (-0.82 to -0.64) and high vapour pressure (12790 Pa at 20°C) (OECD, 2004a: SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 18 - 20 October 2004, Methanol, CAS 67-56-1).


The saturation concentration in water of the hydrolysis product, [3-(2,3-epoxypropoxy)propyl]silanetriol is limited by condensation reactions to approximately 1000 mg/l. However, it is very hydrophilic (calculated solubility is 1.0E+06 mg/l using a QSAR method) and has a low log Kow (-2.6, predicted).

It is not expected to be surface active and is not expected to undergo significant dissociation within the environmentally-relevant range. The first dissociation constant of a structurally analogous silanetriol (phenylsilanetriol) has been reported to be around pKa of 10. It is much less volatile than the parent substance (vapour pressure = 1.7E-05 Pa at 25°C, predicted).


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