Registration Dossier
Registration Dossier
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EC number: 617-969-6 | CAS number: 87135-01-1
Endpoint summary
Administrative data
Description of key information
Additional information
1,6-Bis(trimethoxysilyl)hexane is a liquid at standard temperature and pressure, with a measured melting point of <-20°C, and a measured boiling point of 294°C. It has a measured density of 1.01 g/cm3 at 25°C, a predicted kinematic viscosity of 5.6 mm2/s at 20°C and a measured vapour pressure of 0.081 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 129°C and a measured boiling point of 294°C. It has a measured auto-ignition temperature of 238°C, and is not explosive and not oxidising on the basis of examination of the chemical structure.
In contact with water 1,6 -bis(trimethoxysilyl)hexane reacts rapidly (half-life 5.2 hours at pH 7, 0.08 hours at pH 5, 0.15 hours at pH 9 and 25°C) to produce 1,6 -bis(trihydroxysilyl)hexane and methanol according to the following equation:
(CH3O)3Si(CH2)6Si(OCH3)3+ 3H2O →(OH)3Si(CH2)6Si(OH)3+ 6CH3OH
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 are assessed instead.
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 2004).
The saturation concentration in water of the silanol hydrolysis product, 1,6-bis(trihydroxysilyl)hexane is limited by condensation reactions that can occur over time at loadings above approximately 100 mg/l. However, it is very hydrophilic (calculated solubility is 1.0E+06 mg/l at 20°C using a QSAR method) and has a low log Kow (-3.5, predicted). It is less volatile than the parent substance (vapour pressure of 1.2E-09 Pa at 25°C, predicted). The first dissociation constant of a structurally analogous silanetriol (phenylsilanetriol) has been reported to be around pKa= 10.
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