Registration Dossier
Registration Dossier
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EC number: 280-084-5 | CAS number: 82985-35-1
Endpoint summary
Administrative data
Description of key information
Additional information
- Concentration of the silanol; the greater the initial concentration, the greater the degree of condensation. Significant condensation is not expected at concentrations less than approximately 100 mg/l, but is dependent on specific conditions.
- pH; the condensation reaction may be either acid or base catalysed.
- Temperature.
- Other species present.
- The nature of the R group
Physico-chemical properties
Table 1.3.1 gives an overview of the physicochemical properties of the substance and the evaluation undertaken for each endpoint.
Bis(trimethoxysilylpropyl)amine is a liquid at standard temperature and pressure. No freezing temperature was determined but a glass transition at -118°C was observed. The substance has a measured boiling point of 303.4°C. It has a predicted density of 0.9g/cm3at 25°C, a predicted static viscosity of 5.7 mm2/s at 20°C and a predicted vapour pressure of 1.3E-02 Pa at 25°C.
The substance is classified as a non-flammable liquid on the basis of a measured flash point of 112.7°C and a boiling point of 303.4°C. It has a measured self-ignition temperature of 270°C, and is not explosive and not oxidising on the basis of chemical structure. A dissociation constant value of 10.21 for the amine group (at 20°C) has been reported.
In contact with water Bis(trimethoxysilylpropyl)amine reacts rapidly (half-life approximately7 hours at pH 7 and 20 - 25°C) to produce
bis(trihydroxysilylpropyl)amine and methanol according to the following equation:
[(CH3O)3SiCH2CH2CH2]NH + 3H2O ¿ [(HO)3SiCH2CH2CH2]NH + 3CH3OH
Therefore, requirements for testing of the water-based physicochemical properties for the substance and measurement of the surface tension are waived on the basis of instability in water. The properties of the hydrolysis products are assessed instead.
The silanol hydrolysis product,bis(trihydroxysilylpropyl)amine, is predicted to be very soluble in water 20oC (1E+06 mg/l) and has a log Kowof -4.0 (predicted). It is less volatile than the parent substance with a vapour pressure of <1.0E-06 at 25°C (predicted). The first dissociation constant of a structurally analogous silanetriol (phenylsilanetriol) has been reported to be around pKa10.
Methanol is miscible with water, has low log Kow(-0.82 to -0.64) and high vapour pressure (12790 Pa at 20°C) (OECD, 2004).
Silanetriols may undergo condensation reactions to give siloxane dimers, oligomers and polymers, according to the scheme:
RSi(OH)3 ¿ RSi(OH)2OSi(OH)2R ¿ RSi(OH)2O[Si(R)(OH)O]nSi(OH)2R
(where R is an alkyl or aryl side-chain)
A highly cross-linked gel may form. The degree of condensation that will occur may vary with:
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